PATENT DOCUMENT

Publication Number: US-11585749-B2
Application Number: US-202017063483-A
Country: US
Kind Code: B2

Title: Reference switch architectures for noncontact sensing of substances

Abstract:
This relates to systems and methods for measuring a concentration and type of substance in a sample at a sampling interface. The systems can include a light source, optics, one or more modulators, a reference, a detector, and a controller. The systems and methods disclosed can be capable of accounting for drift originating from the light source, one or more optics, and the detector by sharing one or more components between different measurement light paths. Additionally, the systems can be capable of differentiating between different types of drift and eliminating erroneous measurements due to stray light with the placement of one or more modulators between the light source and the sample or reference. Furthermore, the systems can be capable of detecting the substance along various locations and depths within the sample by mapping a detector pixel and a microoptics to the location and depth in the sample.

Claims:
What is claimed is: 
     
       1. A system for taking a measurement, comprising:
 a light source configured to output light to a sample; 
 a lens located at an interface of the system and configured to receive a first portion of the light from a first location within the sample and a second portion of the light from a second location within the sample; 
 a microlens array, comprising:
 a first microlens configured to receive the first portion of the light from the lens and direct the first portion of the light to the detector; and 
 a second microlens configured to receive the second portion of the light from the lens and direct the second portion of the light to the detector. 
 
 
     
     
       2. The system of  claim 1 , further comprising a reference, wherein:
 the light comprises first light that is output to the sample and second light that is output to the reference; and 
 the microlens array further comprises a third microlens configured to:
 receive the second light from the reference; and 
 direct the second light to the detector. 
 
 
     
     
       3. The system of  claim 2 , wherein:
 the detector includes a plurality of detector pixels; and 
 the third microlens is configured to:
 split the second light from the reference; and 
 direct the split second light to at least two detector pixels of the plurality of detector pixels. 
 
 
     
     
       4. The system of  claim 2 , wherein:
 the third microlens is a different type of lens than the first microlens and the second microlens; and 
 the third microlens comprises one of a negative lens or a prism wedge. 
 
     
     
       5. The system of  claim 1 , further comprising one or more input regions located at the interface of the system; wherein:
 the microlens array includes a fourth microlens that configured to:
 receive the light from the light source; and 
 direct the light from the light source to the one or more input regions. 
 
 
     
     
       6. The system of  claim 1 , wherein:
 the detector includes a plurality of detector pixels comprising a first detector pixel and a second detector pixel; 
 the first microlens directs the light from the first location to the first detector pixel; and 
 the second microlens directs the light from the second location to the second detector pixel. 
 
     
     
       7. The system of  claim 1 , further comprising a patterned aperture including one or more opaque regions; wherein:
 at least one of the one or more opaque regions is located between the first microlens and the second microlens. 
 
     
     
       8. The system of  claim 1 , further comprising an optics unit, the optics unit comprising:
 first optics that receives the light from the lens and directs the light from the lens to the detector; and 
 second optics that receives the light from the lens and directs the light from the lens to the detector. 
 
     
     
       9. The system of  claim 1 , further comprising an aperture, the aperture comprising:
 a first opening configured to receive the light from the first location; and 
 a second opening configured to receive the light from the second location; wherein:
 the first opening selectively directs the light from the first location to the detector; and 
 the second opening selectively directs the light from the second to the detector. 
 
 
     
     
       10. The system of  claim 1 , further comprising a second detector and a beamsplitter, wherein:
 the beamsplitter splits light from the first location; and 
 at least a portion of the light split by the beamsplitter is directed to the second detector. 
 
     
     
       11. A method from taking a measurement of a sample using a device, comprising:
 emitting light from the device towards a sample interface; 
 receiving at a lens located at an interface of the device a first portion of the light from a first location within the sample and a second portion of the light from a second location within the sample; 
 directing the first portion of the light from the lens to a detector using a first microlens of a microlens array; and 
 directing the second portion of the light from the lens to the detector using a second microlens of the microlens array. 
 
     
     
       12. The method of  claim 11 , wherein:
 the operation of emitting the light comprises:
 emitting a first light toward the sample interface; and 
 emitting a second light toward a reference; and 
 
 the method further comprises directing the second light from the reference to the detector using an optics. 
 
     
     
       13. The method of  claim 11 , further comprising:
 splitting light received from a reference; and 
 directing the split light to at least two detector pixels included in the detector. 
 
     
     
       14. The method of  claim 11 , wherein:
 the detector includes a first detector pixel and a second detector pixel; 
 the operation of directing the first portion of the light from the lens comprises directing the first portion of the light from the lens to the first detector pixel; and 
 the operation of directing the second portion of the light from the lens comprises directing the second portion of the light from the lens to the second detector pixel. 
 
     
     
       15. The method of  claim 11 , further comprising passing the light from the lens through an aperture to the detector. 
     
     
       16. The method of  claim 15 , wherein passing the light through the aperture comprises changing one or more of a path length or an angle of incidence of the light. 
     
     
       17. The method of  claim 11 , wherein the detector is a first detector, the method further comprising:
 splitting the light from the lens using a beamsplitter; and 
 directing at least a portion of the split light to a second detector. 
 
     
     
       18. A system for measuring a concentration of a substance in a sample, comprising:
 a light source configured to output a first light to the sample and a second light to a reference; 
 a lens configured to receive a portion of the first light from a location of the sample; 
 a detector comprising:
 a first detector region; and 
 a second detector region; and 
 
 a microlens array comprising:
 a first microlens configured to receive the first light from the output region and direct the light from the output region to the first detector region; and 
 a second microlens configured to receive the second light from the reference and direct the second light to the second detector region. 
 
 
     
     
       19. The system of  claim 18 , wherein:
 the detector further comprises a third detector region; 
 the location is a first location; 
 the lens configured to receive a first portion of the first light from the first location and receive a second portion of the first light from a second location of the sample; and 
 the microlens array further comprises a third microlens configured to receive the second portion of the first light from lens and direct the second portion of the first light to the third detector region. 
 
     
     
       20. The system of  claim 18 , wherein the second optics is configured to:
 direct a first portion of the second light to the second detector region; and 
 direct a second portion of the second light to the first detector region.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/751,095, filed Feb. 7, 2018, which is a National Phase Patent Application under 35 U.S.C. § 371 of International Application No. PCT/US2016/049330, filed Aug. 29, 2016, which claims priority to U.S. Provisional Patent Application No. 62/213,004, filed Sep. 1, 2015, which are hereby incorporated by reference in their entirety. 
    
    
     FIELD 
     This relates generally to a reference switch architecture capable of detecting one or more substances in a sample at a sampling interface, and more particularly, capable of reconstructing one or more optical paths in the sample. 
     BACKGROUND 
     Absorption spectroscopy is an analytical technique that can be used to determine the concentration and type of substance in a sample at a sampling interface. Conventional systems and methods for absorption spectroscopy can include emitting light at the sample. As light transmits through the sample, a portion of the light energy can be absorbed at one or more wavelengths. This absorption can cause a change in the properties of the light exiting the sample. The properties of the light exiting the sample can be compared to the properties of the light exiting a reference, and the concentration and type of substance in the sample can be determined based on this comparison. 
     Although the comparison can determine the concentration and type of substance in the sample, the measurements and determination can be erroneous due to the inability to differentiate and compensate for stray light and fluctuations, drift, and variations early on, instead of after a large number (e.g., tens or hundreds) of sample points are measured. Furthermore, some conventional systems and methods may not be capable of measuring the concentration at multiple locations within the sample. Those systems and methods that can be capable of measuring the concentration at multiple locations can require complicated components or detection schemes to associate the depths of the locations within the sample or path lengths of the light exiting the sample. 
     SUMMARY 
     This relates to systems and methods for measuring a concentration of a substance in a sample when the concentration in the sample is low or the SNR is low (e.g., SNR&lt;10 −4  or 10 −5 ). The systems and methods disclosed can be capable of accounting for fluctuations, drift, and/or variations originating from the light source, one or more optics, and the detector in the system by sharing one or more components between the light path for measuring the sample optical properties and the light path for measuring the reference optical properties. Additionally, the systems can be capable of differentiating between different types of drift and can be capable of eliminating erroneous measurements due to stray light with the placement of one or more modulators between the light source and the sample or reference. Furthermore, the systems can be capable of detecting the substance along various locations and depths within the sample by mapping a detector pixel in a detector array and a microoptics in a microoptics unit to the location and depth in the sample. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an exemplary system comprising multiple detectors for measuring the concentration of a substance in a sample according to examples of the disclosure. 
         FIG.  2    illustrates an exemplary process flow for measuring the concentration and type of substance in a sample using a system comprising multiple detectors according to examples of the disclosure. 
         FIG.  3    illustrates an exemplary system comprising a shared detector for measuring the concentration and type of substance in a sample according to examples of the disclosure. 
         FIG.  4    illustrates an exemplary process flow for measuring the concentration and type of substance in a sample using a system comprising a shared detector according to examples of the disclosure. 
         FIG.  5    illustrates an exemplary plot of absorbance measurements for determining the concentration and type of substance according to examples of the disclosure. 
         FIG.  6    illustrates an exemplary system comprising a modulator located between the light source and the sample for measuring the concentration and type of substance in a sample according to examples of the disclosure. 
         FIG.  7    illustrates an exemplary process flow for measuring the concentration and type of substance in a sample using a system comprising a modulator located between the light source and the sample according to examples of the disclosure. 
         FIG.  8    illustrates an exemplary system comprising a modulator located between the light source and the sample for measuring the concentration and type of substance in a sample according to examples of the disclosure. 
         FIG.  9    illustrates an exemplary process flow for measuring the concentration and type of substance in a sample using a system comprising a modulator located between the light source and the sample according to examples of the disclosure. 
         FIGS.  10 A- 10 C  illustrate exemplary plots of absorbance measurements used for determining the concentration and type of substance according to examples of the disclosure. 
         FIG.  11    illustrates an exemplary process flow during a calibration procedure according to examples of the disclosure. 
         FIG.  12    illustrates an exemplary block diagram of an exemplary system capable reconstructing a plurality of optical paths originating from different locations within a sample and capable of resolving different path lengths of the plurality of optical paths according to examples of the disclosure. 
         FIG.  13    illustrates a cross-sectional view of an exemplary system capable of measuring different locations in the sample and capable of resolving different light paths associated with the different locations in the sample according to examples of the disclosure. 
         FIGS.  14 A- 14 B  illustrate cross-sectional views of exemplary systems configured for determining a concentration and type of substance located in a sample using shared optics according to examples of the disclosure. 
         FIG.  15    illustrates a cross-sectional view of an exemplary system configured for determining a concentration and type of substance located in a sample and configured to reduce or eliminate light reflections or scattering at the sample-system interface according to examples of the disclosure. 
         FIG.  16 A  illustrates a cross-sectional view of an exemplary system configured for determining a concentration and type of substance located in a sample according to examples of the disclosure. 
         FIG.  16 B  illustrates a cross-sectional view of an exemplary polarization sensitive system according to examples of the disclosure. 
         FIG.  17    illustrates a cross-sectional view of an exemplary system configured for determining a concentration and type of substance in a sample according to examples of the disclosure. 
         FIGS.  18 - 19    illustrate top views of a surface of exemplary systems configured for determining a concentration and type of substance located in a sample according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the various examples. 
     Representative applications of methods and apparatus according to the present disclosure are described in this section. These examples are being provided solely to add context and aid in the understanding of the described examples. It will thus be apparent to one skilled in the art that the described examples may be practiced without some or all of the specific details. Other applications are possible, such that the following examples should not be taken as limiting. 
     Various techniques and process flow steps will be described in detail with reference to examples as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects and/or features described or referenced herein. It will be apparent, however, to one skilled in the art, that one or more aspects and/or features described or referenced herein may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not obscure some of the aspects and/or features described or referenced herein. 
     Further, although process steps or method steps can be described in a sequential order, such processes and methods can be configured to work in any suitable order. In other words, any sequence or order of steps that can be described in the disclosure does not, in and of itself, indicate a requirement that the steps be performed in that order. Further, some steps may be performed simultaneously despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modification thereto, does not imply that the illustrated process or any of its steps are necessary to one or more of the examples, and does not imply that the illustrated process is preferred. 
     This disclosure relates to systems and methods for measuring a concentration and type of substance in a sample at a sampling interface. In some examples, the concentration in the sample can be low, or the SNR can be low (e.g., SNR&lt;10 4  or 10 −5 ). The systems can include a light source, optics, one or more modulators, a reference, a detector, and a controller (or logic). The systems and methods disclosed can be capable of accounting for fluctuations, drift, and/or variations originating from the light source, one or more optics, and the detector by sharing one or more components between the light path for measuring the sample optical properties and the light path for measuring the reference optical properties. Additionally, the systems can be capable of differentiating between different types of drift and can be capable of eliminating erroneous measurements due to stray light with the placement of one or more modulators between the light source and the sample or reference. Furthermore, the systems can be capable of detecting the substance along various locations and depths within the sample by mapping a detector pixel in a detector array and a microoptics in a microoptics unit to the location and depth in the sample. 
     For substances in a sample, each substance can have a signature in a certain wavelength regime, indicated by the location of one or more absorbance peaks. One exemplary wavelength regime can be short-wavelength infrared (SWIR). A substance can absorb higher amounts of energy at one or more wavelengths and can absorb lower amounts of energy at other wavelengths, forming a spectral fingerprint unique to the substance. The determination of the type of substance in the sample can be performed by matching the pattern of the one or more absorbance peaks to this spectral fingerprint. Additionally, the concentration of the substance can be based on the amount of absorption. 
     The sample at a sampling interface can comprise multiple substances that can modify light incident. Of the multiple substances, one or more substances can be a substance of interest and other substances may not be of interest. In some examples, the substances not of interest can absorb more incident light than the substance of interest. Additionally, spectral artifacts can “mask” the absorbance peaks of the one or more substances of interest. Both the spectral artifacts and the absorption of substances not of interest can make detection of the substance of interest difficult. Furthermore, there can be an inhomogeneous distribution of the one or more substances in the sample, which can produce variations in the optical properties (e.g., linear birefringence, optical activity, diattenuation) of the sample. 
     Absorption spectroscopy is an analytical technique that can be used to determine the concentration and type of substance in a sample. Light can have an initial intensity or energy when emitted from a light source and incident on a sample. As the light is transmitted through the sample, a portion of the energy can be absorbed at one or more wavelengths. This absorption can cause a change (e.g., loss) in the intensity of the light exiting the sample. As the concentration of the substance in the sample increases, a higher amount of energy can be absorbed, and this can be represented by the measured absorbance as:
 
 A= 2−log( T )  (1)
 
where T is the transmittance of the light exiting the sample.
 
     The amount of light exiting the sample after being at least partially absorbed by a substance can decrease exponentially as the concentration of the substance in the sample increases. Given the relationship between absorbance and transmittance stated in Equation 1, a linear relationship can exist between absorbance and the concentration of the substance in the sample. With this relationship, the concentration of the substance in the sample can be calculated using a reference and a proportional equation, defined as: 
                       A   sample       A   reference       =       C   sample       C   reference               (   2   )               
where A sample  and A reference  are the sample absorbance and reference absorbance, respectively, and C sample  and C reference  are the concentrations of the substance in the sample and in the reference, respectively. In some examples, the substance can include one or more chemical constituents, and the measurement can be used to determine the concentration of each chemical constituent present in the sample.
 
       FIG.  1    illustrates an exemplary system and  FIG.  2    illustrates an exemplary process flow for measuring the concentration of a substance in a sample using a system comprising multiple detectors according to examples of the disclosure. System  100  can include light source  102  controlled by controller  140  through signal  104 . Light source  102  can emit multi-band or multi-wavelength light  150  towards monochromator  106  (step  202  of process  200 ). A monochromator is a component that can select one or more discrete wavelengths from multi-wavelength light  150 . In some examples, monochromator  106  can comprise an entrance slit configured to exclude unwanted or stray light. The monochromator can be coupled with one or more interference or absorption filters, prisms, or diffraction gratings for wavelength selection. Monochromator  106  can separate light  150  into one or more discrete wavelengths forming light  152  (step  204  of process  200 ). Light  152  can be incident on beamsplitter  110 . A beamsplitter is an optical component that can split a beam of light into multiple beams of light. Here, beamsplitter  110  can split light  152  into two light beams: light  154  and light  164  (step  206  of process  200 ). 
     Light  154  can be incident on sample  120 . A portion of light can be absorbed by the substance in sample  120 , and a portion of light can transmit through sample  120  (step  208  of process  200 ). The portion of light that transmits through sample  120  can be represented as light  156 . Light  156  can comprise a set of photons that can impinge upon the active area of detector  130 . Detector  130  can respond to or measure light or photons impinging on the active area (step  210  of process  200 ) and can generate electrical signal  158 , which can be indicative of the properties of light  156  (step  212  of process  200 ). Electrical signal  158  can be input into controller  140 . 
     Light  164  can be directed towards mirror  112  (step  214  of process  200 ). Mirror  112  can be any type of optics capable of directing or redirecting light towards reference  122 . In some examples, the system can, additionally or alternatively, include, but is not limited to, non-reflective component(s) (e.g., curved waveguide) for light redirection. In some examples, system  100  can include other types of optics such as light guides, diffraction gratings, or a reflectance plate. Light  164  can be incident on reference  122 . A portion of light  164  can be absorbed by the substance in reference  122 , and a portion of light  164  can transmit through reference  122  as light  166  (step  216  of process  200 ). Light  166  can comprise a set of photons that can impinge upon the active area of detector  132 . In some examples, detector  130  and detector  132  can be matched detectors. That is, detector  130  and detector  132  can have similar characteristics including, but not limited to, the type of detector, the operating conditions, and performance. Detector  132  can respond to or measure light or photons impinging on the active area (step  218  of process  200 ) and can generate an electrical signal  168  indicative of the properties of light  166  (step  220  of process  200 ). Electrical signal  168  can be input into controller  140 . 
     Controller  140  can receive both signal  158  and signal  168 . In some examples, signal  158  can include the sample absorbance (indicated as A sample  in Equation 2), and signal  168  can include the reference absorbance (indicated as A reference  in Equation 2). Controller  140  can divide the sample absorbance by the reference absorbance to obtain a ratio. The concentration of the substance in reference  122  can be a pre-determined or known value. Thus, controller  140  can use the ratio of the sample and reference absorbance and the known concentration of the substance in the reference to determine the concentration of the substance in the sample (step  222  of process  200 ). 
     One advantage to determining the composition of the substance in the sample using system  100  (illustrated in  FIG.  1   ) can be that fluctuations, drift, and/or variations originating from the light source, and not originating from changes in the composition of the substance, can be compensated. For example, if the properties of light  152  emitted from light source  102  unexpectedly change, both light  154  and light  164  can be equally affected by this unexpected change. As a result, both light  156  and light  166  can also be equally affected such that the change in light can be canceled when controller  140  divides signal  158  by signal  168 . However, since system  100  includes two different detectors (e.g., detector  130  and detector  132 ) for the absorbance measurements, fluctuations, drift, and/or variations originating from the detectors themselves may not be compensated. Although detector  130  and detector  132  can be matched (i.e., have the same characteristics), the rate or effect that various factors unrelated to the substance, such as environmental conditions, can have on the different detectors may not be the same. One skilled in the art would appreciate that the same characteristics can include tolerances that result in a 15% deviation. With differing effects to the different detectors, only one signal, and not both signals, can be perturbed. Instead of controller  140  realizing that there is a factor unrelated to the substance that has perturbed only one signal, controller  140  can erroneous calculate this perturbation as a difference in the concentration of sample  120  compared to the reference  122 . Alternatively or additionally, controller  140  can mistake the type of substance if the perturbation leads to change in the spectral fingerprint. 
     There can be many sources of fluctuations, drift, and variations. One exemplary drift can be an initialization drift due to “warming up” the components. While the user can wait a certain time until such initialization drift has stabilized, this may not be a suitable solution in certain applications. For example, in systems where low power consumption is desired, certain components can be turned off when not in use to conserve power and then switched on when in use. Waiting for the components to warm up may become frustrating for the user depending on how long it would take for stabilization. Furthermore, the power consumed while waiting may consume power such that the benefit of turning off the components may be negated. Another exemplary drift can be due to noise. For example, 1/f noise can be present due to randomly changing non-ohmic contacts of the electrodes and/or influences from surface state traps within a component. With random changes, not only are the changes unpredictable, but also may affect the different detectors in a different manner Another exemplary drift can be thermal drift due to variations in temperature and/or humidity of the ambient environment, which may also affect the different detectors in a different manner. 
     Regardless of the source of the fluctuations, drift, and variations, the effect of having a detector measure the sample and a different detector measure the reference can lead to an unwanted change in the sensitivity, detectivity, and/or absorbance spectrum. Since the light path traveling through the sample can be different from the light path traveling through the reference and there can be many non-shared components or unmapped correlations between the two paths, any change in signal due to mismatch between the light paths may not be differentiated from the change in signal due to the substance of interest. 
     Since light source  102  in system  100  can be shared, drift and instabilities originating from light source  102  can be compensated for. However, drift or instabilities originating from components that are not shared (i.e., not common) along both light paths may not be compensated for. Moreover, the measurement capabilities of the system can be limited in situations where the detectors are shot noise limited. Shot noise is the noise or current generated from random generation and flow of mobile charge carriers. With shot noise limited detectors, the different detectors can have random and/or different noise floors. As a result, system  100  (illustrated in  FIG.  1   ) may not be suitable for high sensitivity or low signal measurements. 
       FIG.  3    illustrates an exemplary system and  FIG.  4    illustrates an exemplary process flow for measuring the concentration and type of substance in a sample using a system comprising a shared detector according to examples of the disclosure. System  300  can include light source  302  controlled by controller  340  through signal  304 . Light source  302  can emit multi-wavelength light  350  towards monochromator  306  (step  402  of process  400 ). Monochromator  306  can separate multi-wavelength light  350  into one or more discrete wavelengths of light comprising light  352  (step  404  of process  400 ). Light  352  can be directed towards beamsplitter  310 , which can then split light into two light beams: light  354  and light  364  (step  406  of process  400 ). 
     Light  354  can be incident on sample  320 . A portion of light can be absorbed by the substance in sample  320 , and a portion of light can transmit through sample  320  (step  408  of process  400 ). The portion of light that transmits through the sample can be referred to as light  356 . Light  356  can be directed towards mirror  314 . Mirror  314  can change the direction of propagation of light  356  toward selector  324  (step  410  of process  400 ). 
     Light  364  can be incident on mirror  312 . Mirror  312  can change the direction of propagation of light towards reference  322  (step  412  of process  400 ). A portion of light  364  can be absorbed by the chemical substance in reference  322 , and a portion of light  364  can transmit through reference  322  (step  414  of process  400 ). The portion of light that transmits through reference  322  can be referred to as light  366 . 
     Both light  356  and  366  can be incident on selector  324 . Selector  324  can be any optical component capable of moving or selecting the light beam to direct towards the chopper  334 . Chopper  334  can be a component that periodically interrupts the light beam. System  300  can alternate in time between chopper  334  modulating light  356  and modulating light  366 . Light transmitting through chopper  334  can be incident on the active area of detector  330 . Both light  356  and light  366  can each comprise a set of photons that impinge upon the active area of detector  330 . Detector  330  can respond to or measure light or photons impinging on the active area and can generate an electrical signal indicative of the properties of light. 
     In a first time, chopper  334  can modulate light  356  (step  416  of process  400 ). Detector  330  can measure light  356  that has transmitted through the sample  320  (step  418  of process  400 ) and can generate an electrical signal  358  indicative of the properties of light  356  (step  420  of process  400 ). In a second time, chopper  334  can modulate light  366  (step  422  of process  400 ). Detector  330  can measure light  366  that has transmitted through reference  322  (step  424  of process  400 ) and can generate an electrical signal  368  indicative of the properties of light  366  (step  426  of process  400 ). 
     Controller  340  can receive both signal  358  and signal  368  at different times. Signal  358  can include the sample absorbance A sample , and signal  368  can include the reference absorbance A reference . Controller  340  can divide the sample absorbance A sample  by the reference absorbance A reference  (step  428  of process  400 ) to obtain a ratio. The concentration of the substance in the reference  322  can be a pre-determined or known value. Using the ratio of the sample absorbance and the reference absorbance and the concentration of the substance in reference  322 , Equation 2 can be used to determine the concentration of the substance in sample  320 . 
     Although system  300  (illustrated in  FIG.  3   ) can compensate for minor fluctuations, drifts, and/or variations in the detector due to the shared detector, it may be difficult to discern between different types of drift. There can be multiple types of drift, such as zero drift and gain drift. Zero drift refers to a change in the zero level over time, thereby preventing a constant (horizontal) relationship with time. Gain drift refers to a change in the average number of electronic carriers per generated electron-hole pair. That is, gain drift refers to a change in the efficiency or ratio of generated electron-hole pairs to the current response of the detector. In order to discern between the zero drift and the gain drift, the system should be capable of stabilizing one type of drift and then measuring the other. For example, to determine the gain drift from the light source, the system should be DC stabilized (i.e., a stable zero drift). However, due to lack of capability for stabilizing one type of drift in system  300 , in some instances, it may be difficult to discern between zero drift and gain drift. 
     In some instances, the presence of stray light that can be measured by the detector can lead to an erroneous signal and an erroneous determination of the concentration or type of substance. In system  300 , the placement of chopper  334  after light has transmitted through sample  320  or reference  322  can lead to the stray light reaching sample  320  or reference  322 . The stray light may not contribute to the spectroscopic signal, so by allowing the stray light to reach sample  320  or reference  322 , the photons included in the stray can be detected by detector  330 . The photons from the stray light impinging on the active area of detector  330  can lead to erroneous changes in either signal  358  or signal  368 . With a change in signal  358  or signal  368 , controller  340  may not be able to determine whether or how much this change is due to stray light or due to variations in light source  302 . Therefore, system  300  may not be suitable for situations where there can be non-negligible amounts of stray light present. 
     When there is a low concentration of the substance of interest in the sample, a system with increased accuracy and sensitivity, compared to system  100  (illustrated in  FIG.  1   ) and system  300  (illustrated in  FIG.  3   ), may be desired. To measure the concentration of a substance, system  100  (illustrated in  FIG.  1   ) and system  300  (illustrated in  FIG.  3   ) can measure the sample and reference multiple times.  FIG.  5    illustrates an exemplary plot of the absorbance measurements for determining the concentration and type of substance according to examples of the disclosure. The system can begin with calibration phase  570 , where one or more components in the system can be optimized, calibrated, and/or synchronized to minimize errors. Calibration phase  570  can include, for example, only measuring the reference absorbance. Alternatively, a sample with a known, stable concentration of the substance can be placed in the light path where the sample is located. The system can be either on or off. The controller can determine the absorbance and set the “zero level” equal to this absorbance. If the signal has saturated or clipped due to a significant drift, the controller can adjust the light source emission properties until the signal is no longer saturated. 
     Once calibration phase  570  is complete and the zero level has been determined, the system can proceed to measurement phase  572 . In measurement phase  572 , the concentration of the substance in the sample can be measured by sampling several times to generate a plurality of sample points  574 . In some examples, the system can measure tens to hundreds of sample points  574 . Once a certain number of sample points  574  have been obtained, the controller can average the values of the sample points  574  to determine the absorbance. Obtaining multiple sample points and determining the average may be needed because, as illustrated in the figure, the absorbance measurements can include minor perturbations that, if not accounted for, can lead to errors in the determination of the concentration of the substance. In some examples, calibration phase  570  can be repeated to re-zero the zero level when the light source changes emission wavelength, after a pre-determined time has elapsed between consecutive calibration phases, or after a pre-determined number of sample points have been measured. 
     In some instances, the measurement procedure illustrated in  FIG.  5    can have long times between consecutive calibration phases, which can lead to inaccurate average signal measurements due to the set zero level drifting from the actual zero level. The figure illustrates the zero drift or gain drift, where the absorbance signal can start to deviate from a constant (or horizontal) relationship with time due to the zero level or gain level drifting away from the actual zero level or actual gain level, respectively. While the time between consecutive calibration phases can be shortened, there can be a limit on the minimum time period between calibration phases due to the minimum number of sample points that may be needed in order for the average of the sample point values to be an accurate indication of the concentration of the substance in the sample. This can be particularly true in situations where the SNR is low, which can require tens to hundreds of repeated measurements in order to achieve an average absorbance value that is somewhat accurate. 
       FIG.  6    illustrates an exemplary system and  FIG.  7    illustrates an exemplary process flow for measuring the concentration of a substance in a sample using a system comprising a modulator located between the light source and the sample according to examples of the disclosure. System  600  can include light source  602  coupled to controller  640 . Controller  640  can send signal  604  to light source  602 . In some examples, signal  604  can include a current or voltage waveform. Light source  602  can be directed towards filter  606 , and signal  604  can cause light source  602  to emit light  650  towards filter  606  (step  702  of process  700 ). Light source  602  can be any source capable of generating light including, but not limited to, a lamp, a laser, a light emitting diode (LED), an organic LED (OLED), an electroluminescent (EL) source, a super-luminescent diode, any super-continuum source including a fiber-based source, or a combination of one or more of these sources. In some examples, light source  602  can be capable of emitting a single wavelength of light. In some examples, light source  602  can be capable of emitting a plurality of wavelengths of light. In some examples, the plurality of wavelengths can be close to or adjacent to one another providing a continuous output band. In some examples, light source  602  can be a super-continuum source capable of emitting light in at least a portion of both the SWIR and MWIR ranges. A super-continuum source can be any broadband light source that outputs a plurality of wavelengths. In some examples, light source  602  can be any tunable source capable of generating a SWIR signature. 
     Filter  606  can be any type of filter that is capable of tuning or selecting a single wavelength or multiple discrete wavelengths by tuning the drive frequency. In some examples, filter  606  can be an acousto-optic tunable filter (AOTF). In some examples, filter  606  can be an angle tunable narrow bandpass filter. Although not illustrated in the figure, filter  606  can be coupled to controller  640 , and controller  640  can tune the drive frequency of filter  606 . In some examples, filter  606  can be a transmit band filter configured to selectively allow one or more continuous bands (i.e., wavelength ranges) of light to transmit through. Light  650  can comprise multiple wavelengths (step  702  of process  700 ) and after transmitting through filter  606 , can form light  652  comprising one or more discrete wavelengths (step  704  of process  700 ). In some examples, light  652  comprises fewer wavelength of light than light  650 . Light  652  can be directed towards beamsplitter  610 . Beamsplitter  610  can be any type of optic capable of splitting incoming light into multiple light beams. In some examples, each light beam split by the beamsplitter  610  can have the same optical properties. One skilled in the art would appreciate that the same optical properties can include tolerances that result in a 15% deviation. Beamsplitter  610  can split light  652  into two light beams (step  706  of process  700 ): light  654  and light  664 , as illustrated in the figure. 
     Light  654  can transmit through chopper  634 , where chopper  634  can modulate the intensity of light  654  (step  708  of process  700 ). Chopper  634  can be any component capable of modulating the incoming light beam. In some examples, chopper  634  can be an optical chopper. In some examples, chopper  634  can be a mechanical shutter. In some examples, chopper  634  can be a modulator or a switch. Light  654  can transmit through optics  616  (step  710  of process  700 ). Optics  616  can include one or more components configured for changing the behavior and properties, such as the beam spot size and/or angle of propagation, of light  654 . Optics  616  can include, but are not limited to, a lens or lens arrangement, beam directing element, collimating or focusing element, diffractive optic, prism, filter, diffuser, and light guide. Optics  616  can be placed in any arrangement such as a resolved path sampling (RPS) system, confocal system, or any optical system suitable for measuring a concentration and type of substance in sample  620 . The optical can be an optical system capable of resolving multiple angles of incidence on a sample surface and different path lengths of a plurality of optical paths. In some examples, the optical system configured for accepting one or more incident light rays with a path length within a range of path lengths and an angle of incidence within a range of angles, and rejecting optical paths with a path length outside the range of path lengths and with an angle of incidence outside the range of angles. 
     Light  654  can transmit through sample  620 . Energy can be absorbed at one or more wavelengths by the substance in the sample  620 , causing a change in the properties of light  656  exiting the sample (step  712  of process  700 ). In some examples, light  656  can be formed by reflection or scattering of the substance located in the sample. Light  656  can be incident on mirror  614 , which can redirect light  656  towards selector  624  (step  714  of process  700 ). Mirror  614  can be any type of optics capable of changing the direction or angle of propagation of light. For example, mirror  614  can be a concave mirror. In some examples, the system can, additionally or alternatively, include, but is not limited to, non-reflective component(s) (e.g., curved waveguide) for light redirection. 
     Light  664  can be incident on mirror  612  (step  716  of process  700 ). Mirror  612  can redirect light  664  towards detector  630 . Mirror  612  can be any mirror capable of changing the direction or angle of propagation of light. In some examples, mirror  612  can have the same optical properties as mirror  614 . Light  664  can transmit through chopper  636 , which can modulate the intensity of light  664  (step  718  of process  700 ). In some examples, chopper  634  and chopper  636  can have the same chopper characteristics, such as chopping frequency and disc configuration. One skilled in the art would appreciate that the same chopper characteristics can include tolerances that result in a 15% deviation. In some examples, chopper  636  can be a shutter, such as a microelectromechanical (MEMS) shutter. In some examples, chopper  636  can be a modulator or a switch. The modulated light can transmit through filter  608  to generate light  666  (step  720  of process  700 ). Filter  608  can be any type of filter capable of selectively transmitting light. In some examples, filter  608  can be a neutral density filter, blank attenuator, or filter configured for attenuating or reducing the intensity of all wavelengths of light. In some examples, filter  608  can attenuate light by a pre-determined or known constant value or attenuation factor. 
     Both light  656  and light  666  can be incident on selector  624 . Selector  624  can be any optical component capable of moving or selecting the light beam to direct towards detector  630 . System  600  can alternate in time between allowing light  656  to be incident on the active area of detector  630  at one time and allowing light  666  to be incident on the active area of detector  630  at another time. In both situations, light  656  and light  666  can each include a set of photons. The photons can impinge on the active area of detector  630 , and detector  630  can generate an electrical signal indicative of the properties of the incident light or number of impinging photons. Detector  630  can measure the set of photons from light  656  impinging on its active area (step  722  of process  700 ) and can generate an electrical signal  658  (step  724  of process  700 ). Signal  658  can be indicative of the properties of light  656 , which can represent the energy from light  654  that is not absorbed by the substance of interest. Detector  630  can measure the set of photons from light  666  impinging on its active area (step  726  of process  700 ) and can generate an electrical signal  668  (step  728  of process  700 ). Signal  668  can be indicative of the properties of light  664  that was not absorbed by filter  608  and can act as a reference. 
     Detector  630  can be any type of detector capable of measuring or responding to light or photons, such as photodiodes, photoconductors, bolometers, pyroelectric detectors, charge coupled devices (CCDs), thermocouples, thermistors, photovoltaics, and photomultiplier tubes. Detector  630  can include a single detector pixel or a detector array, such as a multi-band detector or a focal plane array (FPA). A detector array can include one or more detector pixels disposed on a substrate. A detector pixel can include one or more detector elements with a common footprint. A detector element can be an element designed to detect the presence of light and can individually generate a signal representative of the detected light. In some examples, detector  630  can be any type of detector capable of detecting light in the SWIR. Exemplary SWIR detectors can include, but are not limited to, Mercury Cadmium Telluride (HgCdTe), Indium Antimonide (InSb), and Indium Gallium Arsenide (InGaAs). In some examples, detector  630  can be a SWIR detector capable of operating in the extended wavelength range (up to 2.7 μm). 
     Controller  640  can receive both signal  658  and signal  668 , where each signal can be received at a different time. Signal  658  can include the sample absorbance A sample , and signal  668  can include the reference absorbance A reference . Controller  640  can divide (or subtract) the sample absorbance A sample  by the reference absorbance A reference  (step  730  of process  700 ) to obtain a ratio. The amount of reduction in intensity produced by filter  608  can be a pre-determined or known value or attenuation factor. Using the ratio of the sample absorbance and the reference absorbance and the attenuation factor for filter  608 , Equation 2 can be used to determine the concentration of the substance of interest in sample  620 . In some examples, controller  640  can compare the reference absorbance to one or more absorbance values stored in a lookup table or in memory to determine the concentration and type of substance in the sample. Although Equation 2 and the above discussion is provided the context of absorbance, examples of the disclosure include, but are not limited to, any optical property such as reflectivity, refractive index, density, concentration, scattering coefficient, and scattering anisotropy. 
     System  600  can be an alternative to system  100  (illustrated in  FIG.  1   ) and system  300  (illustrated in  FIG.  3   ). System  600  can have a shared detector (e.g., detector  630 ) to measure light through sample  620  and filter  608 . Utilizing a shared detector can eliminate or alleviate unpredictable changes in sensitivity, detectivity, and/or absorbance due to differing (or random) fluctuations, drifts, and/or variations. As discussed above, the fluctuations, drifts, and/or variations can be due to initialization, 1/f noise, and/or environmental changes that can affect the two detectors in a different manner Additionally, system  600  can tolerate and discern non-negligible amounts of stray light due to the placement of chopper  634  and chopper  636  in the light path prior to being incident on sample  620  and filter  608 , respectively. Furthermore, unlike system  100  and system  300 , system  600  can account for any fluctuations, drifts, and/or variations originating from both light source  602  and detector  630 . 
     In some examples, attenuation of incoming light by filter  608  by a pre-determined or known constant value can lead to a mismatch between light  656  (i.e., light that transmits through sample  620 ) and light  666  (i.e., light that transmits through filter  608 ). This mismatch can be due to differing absorbance at different wavelengths. At one or more wavelengths, the substance in sample  620  can absorb a large percentage of light, and therefore, a low attenuation factor for filter  608  would be suitable at those one or more wavelengths. At other wavelengths, the same substance and same concentration of that substance in sample  620  can absorb very little light, and therefore, a high attenuation factor for filter  608  would be suitable. Since filter  608  can attenuate by a constant value for all wavelengths of interest, accurate measurements of system  600  can be limited to only one or a small number of wavelengths. Furthermore, a blank attenuator or neutral density filter may not be effective when detecting a low concentration of the substance of interest in the sample if the attenuation factor is not optimal. Therefore, a system that can account for the variations in absorbance with wavelength in sample  620  and can be capable of detecting a low concentration of the substance in the sample may be desired. 
       FIG.  8    illustrates an exemplary system and  FIG.  9    illustrates an exemplary process flow for measuring the concentration of a substance in a sample using a system comprising a modulator located between the light source and the sample according to examples of the disclosure. System  800  can include light source  802  coupled to controller  840 . Controller  840  can send signal  804  to light source  802 . In some examples, signal  804  can include a current or voltage waveform. Light source  802  can be directed towards filter  806 , and signal  804  can cause light source  802  to emit light  850  (step  902  of process  900 ). Light source  802  can be any source capable of emitting light  850 . In some examples, light source  802  can be capable of emitting a single wavelength of light. In some examples, light source  802  can be capable of emitting a plurality of wavelengths of light. An exemplary light source can include, but is not limited to, a lamp, laser, LED, OLED, EL source, super-luminescent diode, super-continuum source, fiber-based source, or a combination of one or more of these sources. In some examples, the plurality of wavelengths can be close to or adjacent to one another providing a continuous output band. In some examples, light source  802  can be any tunable source capable of generating a SWIR signature. In some examples, light source  802  can be a super-continuum capable of emitting light at least in a portion of both the SWIR and MWIR. 
     Filter  806  can be any filter capable of tuning and selecting a single wavelength or multiple discrete wavelengths by tuning the drive frequency. In some examples, filter  806  can be an AOTF. In some examples, filter  606  can be an angle tunable narrow bandpass filter. Although not illustrated in the figure, filter  806  can be coupled to controller  840 , and controller  840  can tune the drive frequency of filter  806 . In some examples, filter  806  can be a transmit band filter configured to selectively allow one or more continuous bands (i.e., wavelength ranges) of light to transmit through. Light  850  can comprise multiple wavelengths and, after transmitting through filter  806 , can form light  852  comprising one or more discrete wavelengths (step  904  of process  900 ). In some examples, light  852  comprises fewer wavelengths of light than light  850 . Light  852  can be directed towards a beamsplitter  810 . Beamsplitter  810  can be any type of optic capable of splitting incoming light into multiple light beams. In some examples, each light beam split by beamsplitter  810  can have the same optical properties. One skilled in the art would appreciate that the same optical properties can include tolerances that result in a 15% deviation. As illustrated in the figure, beamsplitter  810  can split light  852  into two light beams: light  854  and light  864  (step  906  of process  900 ). 
     Light  854  can transmit through chopper  834 , where chopper  834  can modulate the intensity of light  854  (step  908  of process  900 ). Chopper  834  can be any component capable of modulating or periodically interrupting the incoming light beam. In some examples, chopper  834  can be an optical chopper. In some examples, chopper  834  can be a mechanical shutter, such as a MEMS shutter. In some examples, chopper  834  can be a modulator or a switch. Light  854  can transmit through optics  816  (step  910  of process  900 ). Optics  816  can include one or more components configured for changing the behavior and properties, such as the beam spot size and/or angle of propagation, of light  854 . Optics  816  can include, but are not limited to, a lens or lens arrangement, beam directing element, collimating or focusing element, diffractive optic, prism, filter, diffuser, and light guide. Optics  816  can include any type of optical system, such as a RPS system, confocal system, or any optical system suitable for measuring a concentration and type of substance in sample  820 . 
     Light  854  can be directed towards sample  820 . Sample  820  can absorb a portion of light  854  and can transmit a portion of light  854  at one or more wavelengths (step  912  of process  900 ). A portion of light  854  can be absorbed by the substance in sample  820 , and a portion of light  854  can transmit through the sample  820 . The portion of light  854  that transmits through the sample  820  can be referred to as light  856 . In some examples, light  856  can be formed by reflection or scattering of the substance located in sample  820 . Light  856  can be directed towards mirror  814 , and mirror  814  can redirect light  856  towards mirror  814  (step  914  of process  900 ). Mirror  814  can be any type of optics capable of changing the direction of light propagation. In some examples, mirror  814  can be a concave mirror configured to change the direction of light propagation by 90°. In some examples, the system can, additionally or alternatively, include, but is not limited to, non-reflective component(s) (e.g., curved waveguide) for light redirection. 
     The second light path formed by the beamsplitter  810  splitting light  852  can be referred to as light  864 . Light  864  can be directed towards mirror  812 . Mirror  812  can be any type of optics capable of changing the direction of the propagation of light  864 . Mirror  812  can redirect light  864  towards selector  824  (step  916  of process  900 ) by changing its direction of propagation by 90°. In some examples, the system can, additionally or alternatively, include, but is not limited to, non-reflective component(s) (e.g., curved waveguide) for light redirection. 
     Light  864  can transmit through chopper  836 , and chopper  836  can modulate light  864  (step  918  of process  900 ). Chopper  836  can be any component capable of modulating the intensity of the incoming light beam. In some examples, chopper  834  and chopper  836  can have the same chopping characteristics, such as chopping frequency and disc configuration. One skilled in the art would appreciate that the same chopping characteristics can include tolerances that result in a 15% deviation. In some examples, chopper  836  can be a mechanical shutter, such as a MEMS shutter. In some examples, chopper  834  can be an optical modulator or a switch. Light  864  can transmit through optics  818  (step  920  of process  900 ). Optics  818  can include one or more lenses, beam directing elements, collimating or focusing elements, diffractive optics, prisms, filters, diffusers, light guides, or a combination of one or more these optical elements and can be arranged in any arrangement (e.g., RPS system or confocal system) suitable for measuring a concentration and type of substance in sample  820  or reference  822 . In some examples, optics  818  can have the same components, arrangement, and/or characteristics as optics  816 . 
     Light exiting optics  818  can be incident on reference  822  (step  922  of process  900 ). Reference  822  can have one or more known spectroscopic properties (e.g., scattering characteristics, reflection characteristics, or both) that may be selected to match the spectroscopic properties of an intended sample. For example, reference  822  can have one or more spectroscopic properties that match the spectroscopic properties of skin tissue. In some examples, reference  822  can be a copy or a “phantom” replica of sample  820 . In some examples, the absorption spectra of reference  822  can be the same as the absorption spectra of sample  820 . One skilled in the art would appreciate that the same absorption spectra can include tolerances that result in a 15% deviation. A portion of light can be absorbed by reference  822 , and a portion of light can transmit through reference  822 , forming light  866 . After transmitting through reference  822 , light  866  can be directed towards selector  824 . 
     Selector  824  can be any optical component capable of moving or selecting the light beam to direct towards detector  830 . In some examples, selector  824  can be coupled to controller  840 , and controller  840  can send a signal (not shown) to control the movement of selector  824 . In one time, selector  824  can allow light  856  to be incident on the active area of detector  830 . Light  856  can comprise a set of photons, and detector  830  can measure the number of photons in light  856  (step  924  of process  900 ). Detector  830  can generate an electrical signal  858  indicative of the properties (or the number of photons) of light  856  (step  926  of process  900 ). Signal  858  can be sent to controller  840 , which can store and/or process the signal. In another time, selector  824  can allow light  866  to be incident on the active area of detector  830 . Light  866  can also comprise a set of photons, and detector  830  can measure the number of photons in light  866  (step  928  of process  900 ). Detector  830  can generate an electrical signal  868  indicative of the properties (or the number of photons) of light  866  (step  930  of process  900 ). Signal  868  can be sent to controller  840 , which can store and/or process the measured signal. 
     Detector  830  can include single detector pixel or a detector array. In some examples, detector  830  can be any type of detector capable of detecting light in the SWIR. In some examples, detector  830  can be a HgCdTe, InSb, or InGaAs single detector or a FPA. In some examples, detector  830  can be a SWIR detector capable of operating in the extended wavelength range of up to 2.7 μm. 
     Controller  840  can receive both signal  858  and signal  868 , but at different times. Signal  858  can include the sample absorbance A sample , and signal  868  can include the reference absorbance A reference . In some examples, controller  840  can divide (or subtract) the sample absorbance A sample  by the reference absorbance A reference  to determine the concentration of the substance of interest in sample  820  (step  932  of process  900 ). In some examples, controller  840  can compare the reference absorbance to one or more absorbance values stored in a lookup table or in memory to determine the concentration and type of substance in sample  820 . In some examples, signal  858  can differ from signal  868  by the amount of drift from light source  802 , detector  830  or both. The controller  840  can divide (or subtract) signal  858  by signal  868  to determine the amount of drift. Although Equation 2 and the above discussion are provided in the context of absorbance, examples of the disclosure include, but are not limited to, any optical property, such as reflectivity, refractive index, density, concentration, scattering coefficient, and scattering anisotropy. 
     System  800  can include all of the advantages of system  600  while also accounting for variations in the absorbance of sample  820  with wavelength. Although the systems disclosed above illustrate one or more components, such as choppers, optics, mirrors, sample, light source, filters, and detector, one of ordinary skill in the art would understand that the system is not limited to only the components illustrated in the exemplary figures. Furthermore, one of ordinary skill in the art would understand that the location and arrangement of such components are not limited solely to the location and arrangement illustrated in the exemplary figures. 
     While an ideal layout or arrangement of the system would have all components shared between the light path traveling through the sample and the light path traveling the reference, such an arrangement might not be physically possible or feasible. Examples of the disclosure include locating one or more components susceptible to drifting such that these components are common or shared among the two (or multiple) light paths, and locating components not susceptible to drifting (i.e., stable components) to be non-common or not shared among the two (or multiple light paths). For example, components susceptible to drifting can include any electronics or optoelectronic components. Additionally, components not susceptible to drifting can include optics. As illustrated in both system  600  of  FIG.  6    and system  800  of  FIG.  8   , the light source (e.g., light source  602  and light source  802 ) and the detector (e.g., detector  630  and detector  830 ) can be susceptible to drifting, and therefore can be shared between the two light paths (e.g., light  656  and light  666 ; light  856  and light  866 ). On the other hand, choppers (e.g., chopper  634 , chopper  636 , chopper  834 , and chopper  836 ) and optics (e.g., optics  616 , optics  816 , and optics  818 ) can be stable and not susceptible to drifting, and therefore can be individual to each light path. 
       FIG.  10 A  illustrates an exemplary plot of absorbance measurements used for determining the concentration and type a substance according to examples of the disclosure. The absorbance measurement can comprise a plurality of frames  1076 . Each frame  1076  can include one or more calibration phases  1070  and one or more measurement phases  1072 . Each calibration phase  1070  can include one or more steps to measure the noise floor, stray light leakage, or both. For example, the light source in the system can be off or deactivated such that light is not incident on the sample or reference. The detector can take a measurement to determine the amount of dark current and stray light leakage. In some examples, this measurement can be used to determine the zero level. The detector can send this measurement to the controller, and the controller can store the measurement and/or the relevant information in memory. The controller can use this information to determine the actual absorbance of the substance in the sample or reference, or can use this information to set the zero level. 
     Measurement phases  1072  can be interspersed in between the calibration phases  1070 . Measurement phases  1072  can include measuring the absorbance spectrum of the sample during one time and then measuring the absorbance spectrum of the reference during another time, as discussed above. In some examples, any optical property (e.g., reflectivity, refractive index, density, concentration, scattering coefficient, and scattering anisotropy) can be measured instead of, or in addition to, the absorbance. The controller can divide (or subtract) the absorbance spectrum of the sample by the absorbance spectrum of the filter/reference. In some examples, the controller can compare the reference absorbance to one or more absorbance values stored in a lookup table or memory to determine the concentration of the substance in the sample. The measurement can be repeated multiple times within each measurement phase  1072  to generate a plurality of sample points  1074 , and the average of the sample points  1074  can be used. In some examples, the controller can compile sample points  1074  from multiple frames  1076  when determining the average signal value. In some examples, the duration of at least one measurement phase  1072  can be based on a pre-determined or fixed number of sample points  1074 . In some examples, the number of sample points  1074  within at least one measurement phase  1072  can be less than 10. In some examples, the number of sample points  1074  within at least one measurement phase  1172  can be less than 100. In some examples, the duration of at least one measurement phase  1072  can be based on the stability (i.e., time before drifting by more than 10%) of the reference. For example, if the reference remains chemically stable for 60 seconds, the duration of measurement phase  1072  can also be 60 seconds. In some examples, the duration of measurement phase  1072  can be based on the stability of the shared components (e.g., light source and detector). Once a measurement phase  1072  is complete, the controller can proceed to the next frame  1076 . 
     By calibrating more frequently, both the zero drift and the gain drift can be accounted for. Additionally, unlike the procedure illustrated in  FIG.  5   , the drift can be corrected at every frame, which can prevent any significant deviation from the zero level. Furthermore, any fluctuations and/or variations can be compensated for prior to, during, or shortly after the signal begins to deviate. By compensating for the fluctuations, drift, and/or variations and re-zeroing the zero level early on, instead of after tens or hundreds of sample points are measured, the average signal value can be more accurate. In some examples, the number of sample points  1074  taken during measurement phase  1072  can be less than the number of sample points  574  taken during measurement phase  572  (illustrated in  FIG.  5   ). In some examples, measurement phase  1072  can be shorter than measurement phase  572 . 
     In some examples, calibration phrase  1070  can include adjustment of the attenuation factor for those systems that employ a filter as a reference (e.g., filter  608  of system  600  illustrated in  FIG.  6   ).  FIG.  11    illustrates an exemplary process flow during a calibration procedure according to examples of the disclosure. The light source can be turned on or activated to emit light (step  1102  of process  1100 ). In a first time period, the choppers along both light paths (e.g., choppers  634  and  636 ) can be off allowing unmodulated light (e.g., light  654  and light  664 ) to transmit through to the sample (e.g., sample  620 ) and filter (e.g., filter  608 ) (step  1104  of process  1100 ). The detector can measure and generate a first set of electrical signals indicative of the unmodulated light transmitted through the sample and through the reference (step  1106  of process  1100 ). In a second time, the choppers located along both light paths can be turned on or activated such that the choppers are modulating light (step  1108  of process  1100 ). The detector can measure and generate a second set of electrical signals indicative of the modulated light not absorbed by the sample and the reference (step  1110  of process  1100 ). If the absorbance from the unmodulated light is close to (e.g., within 10%) or the same as absorbance from the modulated light (step  1112  of process  1100 ), then the system can increase or continue to increase the properties of light (e.g., light emitted from light source  602 ) (step  1114  of process  1100 ). In some examples, the increase can occur until the absorbance from the first set of electrical signals (i.e., unmodulated light) is no longer close (e.g., within 10% from) to the absorbance from the second set of electrical signals (i.e., modulated light). If the limitations of the light source are reached at any time during these steps (step  1116  of process  1100 ), the attenuation factor can be adjusted instead of adjusting the properties of the light source (step  1118  of process  1100 ). Once the properties of light emitted from the light source, the attenuation factor or both are optimized, the calibration phase can be complete (step  1120  of process  1100 ). Such a calibration procedure can be used to prevent stray light from dominating over light transmitted through the sample. Furthermore, such a calibration procedure can lead to better drift stabilization because drift can be ascertained, and therefore, compensated for. 
     In some examples, the overall time for measuring a certain number of sample points  1074  can be greater than the overall time for measuring the same number of sample points  574  (using the method illustrated in  FIG.  6   ) due to interspersed calibration phases  1070 . However, the procedure illustrated in  FIG.  5    can be limited to measurements where the SNR value is high, as discussed above. Although the overall time may be longer, the capability of measuring at low SNRs can outweigh the compromise with longer overall time. In some examples, the system can be configured for utilizing the procedure illustrated in  FIG.  5    when the SNR values are above a pre-determined threshold and utilizing the procedure illustrated in  FIG.  10    when the SNR values are below a pre-determined threshold. In some examples, the pre-determine threshold can be on the order of 10 −5 . In some examples, the number of sample points  1074  needed for an accurate average signal value may be lower due to the more frequent calibration phases preventing significant deviations and drift. 
       FIG.  10 B  illustrates exemplary plots of absorbance measurements used for determining the concentration and type of substance according to examples of the disclosure. The measurement can include a plurality of measurement phases  1072  interspersed with calibration phases  1070 . The top of  FIG.  10 B  illustrates exemplary absorbance measurements for the sample, and the bottom of  FIG.  10 B  illustrates exemplary absorbance measurements for the reference. For a given calibration phase  1070 , the signal can be sub-modulated, as illustrated in the figure. Similarly, for a given measurement phase  1072 , the signal can, additionally or alternatively, be sub-modulated. By sub-modulating the signal, the absorbance values can be measured sooner than without sub-modulation. Therefore, drift can be accounted and the measured values can be given to the controller earlier on (or within the measurement phase  1072 ), instead of having to wait for the completion of a measurement phase  1072 . In some examples, the method illustrated in  FIG.  10 B  can be used to add in modulation or change the frequency over time. 
       FIG.  10 C  illustrates an exemplary plot of an absorbance measurement used for determining the concentration and type of substance according to examples of the disclosure. In some examples, the reference switching can be nested temporally. As illustrated in the figure, measurement phase  1072  can alternate with measurement phase  1073 , where calibration phase  1070  can be interspersed between the measurement phase  1072  and measurement phase  1073 . Measurement phase  1072  can include measuring the absorbance spectrum of the sample, and measurement phase  1073  can include measuring the absorbance spectrum of the reference. In some examples, two-dimensional drift (e.g., gain and offset) can be corrected when the system is configured for operating at moderate frequencies, and one-dimensional drift (e.g., gain or offset) can be corrected when the system is configured for operating at high frequencies. 
     Due to the inhomogeneous nature of the concentration of substances within a sample, certain applications may require measurements along several different areas and each area can have a different location and path length relative to the optical components in the system. Therefore, a system that can measure several different areas and can recognize the actual or relative differences in path lengths from the optical components to the sample may be desired. 
       FIG.  12    illustrates an exemplary block diagram of an exemplary system capable of measuring several different locations within a sample and capable of recognizing different path lengths, angles of incidence, or both associated with the different locations according to examples of the disclosure. System  1200  can include interface  1280 , optics  1290 , light source  1202 , detector  1230 , and controller  1240 . Interface  1280  can include input regions  1282 , interface reflected light  1284 , reference  1208 , and output regions  1256 . Optics  1290  can include absorber or light blocker  1292 , microoptics  1294 , and light collection optics  1216 . Sample  1220  can be located near, close to, or touching a portion of system  1200 . Light source  1202  can be coupled to controller  1240 . Controller  1240  can send a signal (e.g., current or voltage waveform) to control light source  1202  to emit light towards the sample-system interface. Depending on whether the system is measuring the substance in the sample or in the reference, light source  1202  can emit light towards input regions  1282  or reference  1208 . 
     Input regions  1282  can be configured to allow light to exit system  1200  and be incident on sample  1220 . Light can penetrate a certain depth into sample  1220  and can reflect back towards system  1200 . The reflected light can enter back into system  1200  through output regions  1256  and can be collected by light collection optics  1216 , which can redirect, collimate, and/or magnify the reflected light. The reflected light can be directed towards detector  1230 , and detector  1230  can measure light that has penetrated into sample  1220  and reflected back into system  1230 . Detector  1230  can be coupled to controller  1240  and can send an electrical signal indicative of the reflected light to controller  1240 . 
     Light source  1202  can, additionally or alternatively, emit light towards reference  1208 . Reference  1208  can reflect light towards microoptics  1294 . Microoptics  1294  can redirect, collimate, and/or magnify the reflected light towards detector  1230 . Detector  1230  can measure light reflected from reference  1208  and can generate an electrical signal indicative of this reflected light. Controller  1240  can be configured to receive both the electrical signal indicative of the reflected light and the electrical signal indicative of light reflected from reference  1208  from detector  1230 . 
     In both situations where the system is measuring the substance in the sample and in the reference, light emitted from light source  1202  can reflect off the sample-system interface. Light reflected off the sample-system interface can be referred to as interface reflected light  1284 . In some examples, interface reflected light  1284  can be light emitted from light source  1202  that has not reflected off sample  1220  or reference  1208  and can be due to light scattering. Since interface reflected light  1284  can be unwanted, absorber or light blocker  1292  can prevent interface reflected light  1284  from being collected by microoptics  1294  and light collection optics  1216 , which can prevent interface reflected light  1284  from being measured by detector  1230 . 
       FIG.  13    illustrates a cross-sectional view of an exemplary system capable of measuring the concentration and type of one or more substances at different locations in a sample and capable of resolving the properties of the optical paths associated with the different locations in the sample according to examples of the disclosure. In some examples, the one or more substances of interest can have a low concentration (e.g., more than one order of magnitude less) in the sample than other substances of interest. In some examples, the concentration of the one or more substances can lead to a low SNR (i.e., SNR&lt;10 4  or 10 −5 ). System  1300  can be close to, touching, resting on, or attached to sample  1320 . Sample  1320  can include one or more locations, such as location  1357  and location  1359 , where the substance of interest can be measured. 
     System  1300  can include light source  1302 . Light source  1302  can be configured to emit light  1350 . Light source  1302  can be any source capable of generating light including, but not limited to, a lamp, laser, LED, OLED, EL source, super-luminescent diode, super-continuum source, fiber-based source, or a combination of one or more of these sources. In some examples, light source  1302  can be capable of emitting a single wavelength of light. In some examples, light source  1302  can be capable of emitting a plurality of wavelengths of light. In some examples, light source  1302  can be any tunable source capable of generating a SWIR signature. System  1300  can include input region  1382  located close to or near sample  1320  or an edge of the system. Input region  1382  can be formed by one or more transparent components including, but not limited to, a window, optical shutter, and mechanical shutter. 
     Light  1350  can exit system  1300  through input region  1382 . Light directed at location  1357  in sample  1320  can be referred to as light  1352 . Light  1352  can penetrate through sample  320  and can be incident on location  1357 . In some examples, the angle of incidence of light  1352  at location  1357  can be 45°. In some examples, light  1352  can be a collimated beam. Location  1357  can include a concentration of the substance of interest. Light  1352  can be partially absorbed at location  1357  and can be partially reflected as light  1354 . In some examples, light  1354  can be formed by light transmitting through sample  1320 . Light  1354  can penetrate through sample  1320  and can enter system  1300  at location  1313  of lens  1310 . In some examples, lens  1310  can be in contact or near sample  1320 . In some examples, lens  1310  can be any type of optical component capable of changing the behavior and properties of the incoming light. Lens  1310  can include a plurality of locations, such as location  1313  and location  1317 , where light can to enter system  1300 . In some examples, lens  1310  can include a transparent material. In some examples, lens  1310  can be a Fresnel lens or a lens configured with a large aperture (e.g., an aperture larger than the size of the incoming light beam) and a short focal length. In some examples, lens  1310  can be a Silicon lens. 
     System  1300  can include optics to magnify or project the incoming light beam. In some examples, optics can be a system capable of reimaging or projecting the image of the incoming light at the sample-system interface to another location. For example, the system can reimage the angles of incident light and the position of incident light to another plane (e.g., a plane located closer to the detector array  1330 ). System  1300  can include lens  1316  and lens  1318  configured for reimagining light  1364 . Lens  1316  and lens  1318  can be configured to produce intermediate planes of focus. With intermediate planes of focus, the length of the focus can be extended. For example, to reimage the optical paths at the sample-system interface onto detector array  1330  without magnification, location  1357  can be located a distance f away from lens  1310 . The distance f can be equal to the focal length of lens  1310 . Lens  1316  can be located a distance 2f (i.e., two times the focal length) away from lens  1310 , lens  1318  can be located a distance 2f from lens  1316 , microlens array  1329  can be located a distance 2f away from lens  1318 , and detector array  1330  can be located a distance f away from microlens array  1329 . In some examples, the optics in system  1300  can magnify the image by a factor, such as 2.5× or 5×. 
     Light  1354  can transmit through lens  1316  and  1318  and can be incident on microlens  1323 , included in microlens array  1329 . Microlens array  1329  can comprise a plurality of microlenses, such as microlens  1321 , microlens  1323 , microlens  1325 , and microlens  1327  attached to a substrate. In some examples, microlens  1321 , microlens  1323 , microlens  1325 , and microlens  1327  can be any type of lens and can include any type of material conventionally used in lenses. A microlens can be a small lens or one that is smaller (e.g., a lens with a diameter less than 1 mm) than a conventional lens. In some examples, two or more of microlenses included in the microlens array  1329  can have the same optical and/or physical properties. One skilled in the art would appreciate that the same optical properties and the same physical properties can include tolerances that result in a 15% deviation. Light  1354  can transmit through microlens  1323  and can be incident on detector pixel  1333 . In some examples, microlens array  1329  can be coupled to one or more apertures or apertures. In some examples, microlens array  1329  can be coupled to a patterned aperture, such as an aperture where locations between adjacent microlenses are opaque to prevent light mixing. 
     Detector pixel  1333  can be included in detector array  1330 . Detector array  1330  can include a plurality of detector pixels, such as detector pixel  1331 , detector pixel  1333 , detector pixel  1335 , and detector pixel  1337 . In some examples, detector array  1330  can be a detector including a single detector pixel detector. In some examples, at least one detector pixel can be independently controlled from other detector pixels included in the detector array  1330 . In some examples, at least one detector pixel can be capable of detecting light in the SWIR. In some examples, at least one detector pixel can be a SWIR detector capable of operating between 2.2-2.7 μm. In some examples, at least one detector pixel can be a HgCdTe, InSb, or InGaAs based detector. In some examples, at least one detector pixel can be capable of detecting a position and/or angle of the incoming light beam. Detector pixel  1333  can detect light  1354  and can generate an electrical signal indicative of the properties of light  1354 . Detector array  1430  can transmit the electrical signal to controller  1340 . Controller  1340  can process and/or store the electrical signal. 
     System  1300  can include reflector  1322 . Light source  1302  can emit light  1364 . Light  1364  can be directed at reflector  1322 . Reflector  1322  can include any type of material capable of at least partially reflecting light. Exemplary reflective materials can include, but are not limited to, Titanium (Ti), Cobalt (Co), Niobium (Nb), Tungsten (W), Nickel Chrome (NiCr), Titanium Tungsten (TiW), Chrome (Cr), Aluminum (Al), Gold (Au), and Silver (Ag). The thickness of reflector  1322  can be determined based on the wavelength of light, type of material, and/or composition. In some examples, the size and shape of reflector  1322  can be configured to be larger or the same as the size and/or shape of the light beam included in light  1364 . One skilled in the art would appreciate that the same size and the same shape can include tolerances that result in a 15% deviation. In some examples, reflector  1322  can be configured such that the reflectivity of light  1364  can be greater than 75%. In some examples, reflector  1322  can be configured such that the reflectivity of light  1364  can be greater than 90%. In some examples, the size and shape of reflector  1322  can be such that no or minimal (e.g., less than 10%) amounts of light  1364  is allowed to transmit through reflector  1322  and light  1364  is prevented from penetrating through sample  1320 . In some examples, reflector  1322  can be configured to reflect light  1364  as a specular reflection. In some examples, reflector  1322  can be a spectroscopically neutral blocker. In some examples, the reference can be formed by chopping light  1364  between sample  1320  and reference (e.g., reflector  1322 ). 
     Light  1364  can reflect off reflector  1322  towards lens  1316 . Similar to lens  1312  and lens  1314 , lens  1316  and lens  1318  can reimage or project the image of the incoming light at the sample-system interface. In some examples, lens  1316  and lens  1318  can be configured such that a replica of the optical paths are the sample-system interface is produced onto another plane (e.g., plane where the detector array  1330  is located) without magnification. In some examples, lens  1316  and lens  1318  can be configured such that a magnification, such as 2.5×-5× magnification, is introduced into the replica. Light  1364  can transmit through lens  1316  towards lens  1318 . Light  1364  can transmit through lens  1318  and can be incident on lens  1319 . 
     Lens  1319  can be any type of lens configured for spreading out the incoming light beam. In some examples, lens  1319  can be a negative lens, which can be a lens with a focal length that is negative. In some examples, lens  1319  can be a prism. In some examples, lens  1319  can include a different prism wedge angled for each detector pixel in the detector array  1330 . In some examples, system  1300  can be configured with a beamsplitter for spreading out the incoming light. Lens  1319  can be configured to spread out or divide light into multiple beams, such as light  1366  and light  1367 . In some examples, lens  1319  can spread out light such that each light beam is directed to a different detector pixel on the detector array  1330 . In some examples, lens  1319  can uniformly spread out light such that the optical properties of each light beam are the same. One skilled in the art would appreciate that the same optical properties can include tolerances that result in a 15% deviation. In some examples, lens  1319  can spread out the light beam such that intensities of at least two light beams are different. In some examples, lens  1319  can comprise multiple lenses or microlenses. In some examples, the size and/or size of lens  1319  can be based on the number of detector pixels and/or the intensity of the one or more light beams exiting lens  1319 . In some examples, one or more apertures can be coupled to lens  1319  to control the intensity and/or direction of light exiting lens  1319 . In some examples, lens  1319  or system  1300  can be configured such that light that reflects off a surface of sample  1320  or an edge of system  1300  reflects back into the system (i.e., light that has not traveled through sample  1320 ) and is prevented from being incident on lens  1319 , although stray light or background light can be incident on lens  1319 . 
     Light  1364  can transmit through lens  1319  to form light  1366 . Light  1366  can be incident on detector pixel  1333 . Detector pixel  1333  can detect light  1366  and can generate an electrical signal indicative of the properties of light  1366 . The electrical signal can be transmitted from detector array  1330  to controller  1340 . Controller  1340  can process and/or store the electrical signal. Controller  1340  can utilize the signal information measured from light  1354  to determine the reflectivity or concentration of the substance located at location  1357  within sample  1320  and can utilize the signal information from light  1366  to determine the properties of reflector  1322 . Using any of the above discussed methods, controller  1340  can process both signal information to determine the concentration and type of substance at location  1357  located in sample  1320 . 
     There can be an inhomogeneous distribution of the one or more substances in the sample, which can produce variations in the optical properties (e.g., linear birefringence, optical activity, diattenuation) of the sample. Therefore, a system capable of measuring multiple locations within sample  1320  and corresponding measurements can be beneficial. To measure a different location, such as location  1359  different from location  1357 , light source  1302  can emit light  1350  towards input region  1382 . In some examples, system  1300  can include multiple apertures. For example, system  1300  can include at least two apertures, where light  1352  can exit one aperture and light  1353  can exit the other aperture. Light directed at location  1359  can be referred to as light  1353 . Light  1353  can penetrate through sample  1320  and can be incident on location  1359 . Light  1353  can have any angle of incidence at location  1359  including, but not limited to, 45°. In some examples, light  1353  can be a collimated beam. Location  1359  can include a concentration of one or more substances of interest. Light  1353  can be partially absorbed at location  1359  and can be partially reflected as light  1355 . In some examples, light  1355  can be formed by light transmitting through sample  1320 . Light  1355  can travel through sample  1320  and can enter system  1300  at location  1317  of lens  1310 . Light  1355  can transmit through lens  1310  and can be directed towards lens  1312 . Light  1355  can transmit through lens  1312  and lens  1314  and can be directed towards microlens  1327  of microlens array  1329 . As illustrated in the figure, although lens  1312  and lens  1314  can be shared by light  1354  and light  1355  (i.e., different light beams), the locations where light  1354  and light  1355  are incident on lens  1312  and lens  1314  can be different. Additionally or alternatively, light  1354  and light  1355  can share lens  1312  and lens  1314  by utilizing the lenses at different times. 
     Light  1355  can be incident on microlens  1327 , can transmit through microlens  1327 , and can be incident on detector pixel  1337  of detector array  1330 . Detector pixel  1337  can detect light  1355  and can generate an electrical signal indicative of the properties of light  1355 . Detector array  1330  can transmit the electrical signal to controller  1340 . Controller  1340  can process and/or store the electrical signal. 
     Similar to the discussion given above, a reference signal can be measured using reflector  1322 . Light source  1302  can emit light  1364  towards reflector  1322 . Reflector  1322  can be configured to reflect light  1364  towards detector array  1330 . Light  1364  can transmit through lens  1316  and lens  1318 . Light  1364  can be incident on lens  1319 , which can be configured to spread out the incoming light beam. Lens  1319  can form light  1367 , which can be incident on detector pixel  1337 . Detector pixel  1337  can detect light  1367  and can generate an electrical signal indicative of the properties of light  1367 . The electrical signal can be transmitted from detector array  1330  to controller  1340 . Controller  1340  can process and/or store the electrical signal. Controller  1340  can utilize the signal information measured from light  1355  to determine the reflectivity or concentration of the substance at location  1359  and can utilize the signal information from light  1367  to determine the properties of the reflector  1322 . Controller  1340  can process both signal information to determine the concentration of the substance at location  1359 . In some examples, controller  1340  can determine the properties of reflector  1322  or light  1366  incident on detector pixel  1333  and light  1367  incident on detector pixel  1337  simultaneously without the need for separate measurements. In some examples, location  1357  and location  1359  can have the same depth from the surface of sample  1320 . One skilled in the art would appreciate that the same depth can include tolerances that result in a 15% deviation. In some examples, location  1357  and location  1359  can have different depths from the surface of sample  1320 . Controller  1340  can measure the reflectivity, refractive index, density, concentration, scattering coefficient, scattering anisotropy, absorbance, or any combination of optical properties at both location  1357  and location  1359  and can average the measured values. Although the figure and discussion above relates to two locations in the sample, examples of the disclosure can include any number of locations and are not limited to one or two locations. 
     Although detector array  1330  can be configured to detect the angle or location of incident light, controller  1340  can determine this information based on the detector pixel included in the detector array  1330 . In some examples, light emitted from light source  1302  can be a well-defined (i.e., directional and sharp) light beam and reflected light from sample  1320  can be specular, one or more microlens included in microlens array  1329  can correspond to a different location in sample  1320 . Additionally, one or more detector pixels included in detector array  1330  can be associated with a microlens in the microlens array  1329 . For example, when controller  1340  or detector array  1330  measures light incident on detector pixel  1337 , system  1300  can determine that the incident light originated from location  1359  in sample  1320  due to the association of detector pixel  1337  to location  1359 . Additionally, when controller  1340  or detector array  1330  measures light incident on detector pixel  1333 , system  1300  can determine that the incident light originated from location  1357  due to the association of detector pixel  1333  to location  1357 . In some examples, detector pixel  1331  and detector pixel  1435  can be associated to additional locations (not shown) in sample  1320 . 
     As discussed above, due to the fluctuations, drift, and/or variations that can be introduced into the electrical signal received by the controller, it may be advantageous to share components among one or more light paths that travel through the sample and the light path that reflects off the reflector.  FIG.  14 A  illustrates a cross-sectional view of an exemplary system configured to measure a concentration and type of one or more substances located in a sample using shared optics according to examples of the disclosure. In some examples, the one or more substances of interest can have a low concentration (e.g., more than one order of magnitude less) in the sample than other substances of interest. In some examples, the concentration of the one or more substances can lead to a low SNR (e.g., SNR&lt;10 −4  or 10 −5 ). System  1400  can be close to, touching, resting on, or attached to sample  1420 . Sample  1420  can include one or more locations, such as location  1457  and location  1459 , where the substance can be measured. 
     System  1400  can include light source  1402 . Light source  1402  can be configured to emit light  1450 . Light source  1402  can be any source capable of generating light including, but not limited to, a lamp, laser, LED, OLED, EL source, super-luminescent diode, super-continuum source, fiber-based source, or a combination of one or more of these sources. In some examples, light source  1402  can be capable of emitting a single wavelength of light. In some examples, light source  1402  can be capable of emitting a plurality of wavelengths of light. In some examples, light source  1402  can be any tunable source capable of generating a SWIR signature. System  1400  can include input region  1482  located close to or near sample  1420  or an edge of the system. Input region  1482  can be formed by one or more transparent components including, but not limited to, a window, optical shutter, or mechanical shutter. 
     Light  1450  can exit system  1400  through input region  1482 . Light that exits system  1400  and travels through sample  1420  to location  1457  can be referred to as light  1452 . Light  1452  can have any angle of incidence at location  1457  including, but not limited to, 45°. In some examples, light  1450  can be a collimated beam. Location  1457  can include a concentration of the substance of interest. Light  1452  can be partially absorbed at location  1457  and can be partially reflected as light  1454 . In some examples, light  1454  can be formed by light transmitting through the sample. Light  1454  can penetrate through sample  1420  and can enter system  1400  at location  1413  of optics  1410 . In some examples, optics  1410  can be in contact or near a surface of sample  1420 . In some examples, optics  1410  can be any type of optical component capable of changing the behavior and properties of the incoming light. Optics  1410  can include a plurality of locations, such as location  1413  and location  1417 , where light can enter. In some examples, optics  1410  can include a transparent material. In some examples, optics  1410  can be a Fresnel lens or a lens configured with a large aperture (e.g., an aperture larger than the size of the incoming light beam) and a short focal length. In some examples, optics  1410  can be a Silicon lens. 
     System  1400  can include optics to magnify or project the incoming light beam. Similar to the optics illustrated in and discussed with respect to system  1300  illustrated in  FIG.  13   , the optics in system  1400  can be capable of reimagining the optical paths, including the path lengths, angles of incidence, and exit locations, at the edge of system  1400  to another plane closer to detector array  1430 . To reduce the differences in any fluctuations, drifts, and/or variations between a light path (e.g., light  1452  or light  1453 ) penetrating through the sample  1420  and a light path reflecting off a reference (e.g., reflector  1422 ), system  1400  can share the optics between the two different light paths. System  1400  can include optics  1416  and optics  1418  for reimaging both light that has traveled through sample  1320  and light used as a reference signal. In some examples, optics  1416  and optics  1418  can be configured such that a replica of the image located at the edge of the system can be produced onto another plane (e.g., the plane where the detector array  1430  is located) without magnification. In some examples, optics  1416  and optics  1418  can be configured to introduce a magnification, such as a 2.5×-5× magnification, into the replica. 
       FIG.  14 B  illustrates the system including optics that are shared for both the incident and return or reflected light. Optics  1416  can be shared by light  1450  and light  1464  emitted from light source  1402 , light  1454  and light  1455  that has traveled through sample  1420 , and light  1564  that has reflected off reflector  1422 . In some examples, at least two of the angles of incidence of light  1454 , light  1455 , light  1464 , and light  1450  at optics  1416  and/or optics  1418  can be different. 
     Referring to  FIGS.  14 A- 14 B , light  1454  can transmit through optics  1416  and optics  1418  and can be incident on microoptics  1423 , included in microoptics unit  1429 . Microoptics unit  1429  can comprise a plurality of microlenses, such as microoptics  1423  and microoptics  1427 , attached to a substrate. A microlens can be a small lens or one that is smaller (e.g., a lens with a diameter less than 1 mm) than a conventional lens. In some examples, the microlenses can be any type of lens and can include any type of material conventionally used in lenses. In some examples, two or more of the microlenses can have the same optical and/or physical properties. One skilled in the art would appreciate that the same optical properties and the same physical properties can include tolerances that result in a 15% deviation. Light  1454  can transmit through microoptics  1423  and can be incident on detector pixel  1433 . In some examples, microoptics unit  1429  can be coupled to one or more apertures or apertures. In some examples, microoptics unit  1429  can be coupled to a patterned aperture, such as an aperture where locations between adjacent microoptics are opaque to prevent light mixing. 
     Detector pixel  1433  can be included in detector array  1430 . Detector array  1430  can include a plurality of detector pixels, such as detector pixel  1433  and detector pixel  1437 . In some examples, detector array  1430  can be a single detector pixel detector. In some examples, at least one detector pixel can be independently controlled from other detector pixels included in detector array  1430 . In some examples, at least one detector pixel can be capable of detecting light in the SWIR. In some examples, at least one detector pixel can be a SWIR detector capable of operating between 2.2-2.7 μm. In some examples, at least one detector pixel can be a HgCdTe, InSb, or InGaAs based detector. In some examples, at least one detector pixel can be capable of detecting a path length, angle of incidence, and/or exit location of the incoming light beam. Detector pixel  1433  can detect light  1454  and can generate an electrical signal indicative of the properties of light  1454 . Detector array  1430  can transmit the electrical signal to controller  1440 . Controller  1440  can process and/or store the electrical signal. 
     System  1400  can determine the concentration of the substance in sample  1420  by utilizing the information from light penetrating through the sample in conjunction with the information from light reflecting off reflector  1422 . Light source  1402  can emit light  1464 , which can be directed at reflector  1422 . Reflector  1422  can include any type of material capable of at least partially reflecting light. Exemplary reflective materials can include, but are not limited to, Ti, Co, Nb, W, NiCr, TiW, Cr, Al, Au, and Ag. The thickness of the reflector  1422  can be configured based on the wavelength of light, type of material, and/or composition. In some examples, the size and shape of reflector  1422  can be configured to be larger or the same as the size and/or shape of the light beam included in light  1464 . One skilled in the art would appreciate that the same optical properties and the same physical properties can include tolerances that result in a 15% deviation. In some examples, the reflector  1422  can be configured to reflect greater than 75% of light  1464 . In some examples, reflector  1422  can be configured to reflect greater than 90% of light  1464 . In some examples, the size and shape of reflector  1422  can be such that no or a minimal (e.g., less than 10%) amount of light  1464  is allowed to transmit through reflector  1422 , and light  1464  is prevented from traveling through sample  1420 . In some examples, reflector  1422  can be configured to reflect light  1464  as a specular reflection. In some examples, reflector  1422  can be a spectroscopically neutral blocker. In some examples, the reference can be formed by chopping light  1464  between the sample  1420  and reference (e.g., reflector  1422 ). 
     Light  1464  can reflect off reflector  1422  towards optics  1416 . Light  1464  can transmit through optics  1416  towards optics  1418 . Light  1464  can transmit through optics  1418  and can be incident on optics  1419 . Optics  1419  can be any type of lens configured for spreading out the incoming light beam. In some examples, optics  1419  can be a negative lens, which can be a lens with a focal length that is negative. In some examples, optics  1419  can be a prism. In some examples, optics  1419  can include a different prism wedge angled for each detector pixel in detector array  1430 . In some examples, system  1400  can be configured with a beamsplitter for spreading out the incoming light beam. In some examples, optics  1419  can be configured to spread out or divide light into multiple beams, such as light  1466  and light  1467 . In some examples, optics  1419  can spread out light such that each light beam can be directed to a different detector pixel. In some examples, optics  1419  can uniformly spread out light such that the optical properties of each light beam can be the same. One skilled in the art would appreciate that the same optical properties can include tolerances that result in a 15% deviation. In some examples, optics  1419  can spread out light beam such that intensities of at least two light beams are different. In some examples, optics  1419  can comprise multiple optics or microoptics. In some examples, the size and/or size of optics  1419  can be based on the number of detector pixels and/or the properties of the one or more light beams exiting optics  1419 . In some examples, an aperture can be coupled to optics  1419  to control the properties and/or direction of light exiting optics  1419 . In some examples, optics  1419  or system  1400  can be configured such that light that reflects off a surface of sample  1420  or an edge of system  1400  reflects back into the system (i.e., light that has not traveled through sample  1420 ) and is prevented from being incident on optics  1419 , although stray light or background light can be incident on optics  1419 . 
     Light  1464  can transmit through optics  1419  to form light  1466 . Light  1466  can be incident on detector pixel  1433 . Detector pixel  1433  can detect light  1466  and can generate an electrical signal indicative of the properties of light  1466 . Detector array  1430  can transmit the electrical signal to controller  1440 . Controller  1440  can process and/or store the electrical signal. Controller  1440  can utilize the signal information measured from light  1454  to determine the reflectivity or concentration of the substance at location  1457  and can utilize the signal information from light  1466  to determine the properties of reflector  1422 . Using any of the above discussed methods, controller  1440  can process both signal information to determine the concentration of the substance at location  1457  located in sample  1420 . 
     Similar to measuring the concentration of the substance at location  1557 , the same components can be used to measure the concentration of the substance at location  1559 . Light source  1502  can emit light  1550 , which can exit system  1500  at input region  1582  to form light  1553 . In some examples, system  1500  can include multiple apertures. For example, system  1500  can include at least two apertures, where light  1552  can exit one aperture and light  1553  can exit another aperture. Light  1553  can be incident on location  1559  and can reflect back into system  1500  as light  1555 . Light  1555  can enter system  1500  through optics  1510  at location  1517 . Light  1555  can transmit through optics  1516  and optics  1518  and can be incident on microoptics  1527 . Light  1555  can transmit through microoptics  1527  and can be detected by detector pixel  1537  included in detector array  1530 . Detector pixel  1537  can detect light  1555  and can generate an electrical signal indicative of the properties of the detected light  1555 . The electrical signal can be transmitted from the detector array  1530  to controller  1540 . Controller  1540  can process and/or store the electrical signal. Controller  1440  can utilize the signal information measured from light  1455  to determine the reflectivity or concentration of the substance at location  1459  and can utilize the signal information from light  1467  to determine the properties of the reflector  1422 . Controller  1440  can process both signal information to determine the concentration and type of substance at location  1459 . In some examples, controller  1440  can determine the properties of reflector  1422  (or light  1466  incident on detector pixel  1433 ) and light  1467  incident on detector pixel  1437  simultaneously without the need for separate measurements. In some examples, location  1457  and location  1459  can have the same depth from the surface of sample  1420 . One skilled in the art would appreciate that the same depth can include tolerances that result in a 15% deviation. In some examples, location  1457  and location  1459  can have different depths from the surface of sample  1420 . Controller  1440  can measure the reflectivity, refractive index, density, concentration, scattering coefficient, scattering anisotropy, absorbance, or a combination of the optical properties at both location  1457  and location  1459  and can average the measured values. Although the figure and discussion above relates to two locations in the sample, examples of the disclosure can include any number of locations and are not limited to one or two locations. 
     As illustrated in the figure, system  1400  can include a plurality of microoptics and a plurality of detector pixels, where each microoptics can be coupled to a detector pixel. Each microoptics-detector pixel pair can be associated with a location in the sample. In some examples, the association can be one microoptics-detector pixel pair to one location in the sample. For example, microoptics  1423  and detector pixel  1433  can be associated with location  1457  and microoptics  1427 , and detector pixel  1437  can be associated with location  1459 . Since controller  1440  can associate detector pixel  1433  and detector pixel  1437  to different location (e.g., location  1457  and location  1459 ), controller  1450  can determine and locate different concentrations of the substance for different areas of sample  1420 . 
     While system  1300  (illustrated in  FIG.  13   ) and system  1400  (illustrated in  FIG.  14   ) can account for fluctuations, drift, and/or variations due to shared components (e.g., light source, lenses, and/or detector array), these systems may not account for light that reflects and/or scatters at the edge of the system.  FIG.  15    illustrates a cross-sectional view of an exemplary system configured to measure a concentration and type of one or more substances in a sample and configured to reduce or eliminate light reflections or scattering at the edge of the system according to examples of the disclosure. Similar to system  1300  and system  1400 , system  1500  can comprise multiple components including a light source  1502 , optics  1510 , optics  1516 , optics  1518 , microoptics unit  1527 , detector array  1530 , and controller  1540 . These components can include one or more properties discussed above with reference to the components included in system  600 , system  800 , system  1300 , and system  1400 . 
     The concentration of the substance at location  1557  can be measured using light  1550  exiting system  1500  through input region  1582 , light  1552 , and light  1554  formed by reflecting off location  1557 . Light  1554  can enter system  1500  at location  1513  and can transmit through optics  1510 , optics  1516 , optics  1518 , and microoptics  1523 , included in microoptics unit  1529 . Detector pixel  1533 , included in detector array  1530 , can detect light  1554  and can generate an electrical signal indicative of the optical properties of light  1554 . The concentration of the substance at location  1559  can be measured using light  1550  exiting system  1500  through input region  1582 , light  1553 , and light  1555  formed by reflecting off location  1559 . Light  1555  can enter system  1500  at location  1517  and can transmit through optics  1510 , optics  1516 , optics  1518 , and microoptics  1527 , included in microoptics unit  1529 . Detector pixel  1537 , included in detector array  1530 , can detect light  1555  and can generate an electrical signal indicative of the optical properties of light  1555 . The optical properties of the reference or reflector  1522  can be determined using light  1564  that reflects off reflector  1522 , transmits through optics  1516 , optics  1518 , and optics  1519 . Light  1564  can be spread out by optics  1519  to form light  1566  incident on detector pixel  1533  and light  1567  incident on detector pixel  1537 . Controller  1540  can receive electrical signals indicative of light reflected off location  1557 , location  1559 , and reflector  1522  to determine the concentration of the substance at one or more locations in sample  1520 . 
     Although light  1550  can be directed towards input region  1582  and can be configured for exiting system  1500 , in some examples, light  1550  can scatter or reflect off the edge of system  1500  at one or more locations (e.g., location between input region  1582  and reflect  1522 . Light that scatters or reflects off the edge of the system and back into the system  1500  can be referred to as light  1584 . Since light  1584  can include stray light that reflects back into system  1500 , a portion or all of light  1584  can be incident on one or more microoptics (e.g., microoptics  1523  or microoptics  1527 ). Light that is incident on the microoptics can transmit to one or more detector pixels (e.g., detector pixel  1633  or detector pixel  1637 ) included in the detector array  1530 . As a result, stray light can be measured by detector array  1530 , which can erroneously change the electrical signal that the detector array  1530  can generate and transmit to controller  1540 . Any change in electrical signal due to stray light can lead to a false measurement or determination of the concentration of the substance in the sample  1520 . 
     Therefore, to prevent light  1584  from being detected by detector array  1530 , system  1500  can direct light  1584  towards optics  1516  and optics  1518 . Light  1584  can transmit through optics  1516  and optics  1518  and can be incident on light blocker  1592 . Light blocker  1592  can include any material capable of absorbing or blocking light. In some examples, light blocker  1592  can include any material (e.g., an anti-reflection coating) that prevents incident light from reflecting. In some examples, light blocker  1592  can include any material that reflects at wavelengths different from the detection wavelengths of detector array  1530 . In some examples, system  1500  can, additionally or alternatively, include an anti-reflection coating at one or more locations along the edge of the system. 
     Examples of the disclosure can include other types of optics or optic systems and are not limited to the systems illustrated in  FIGS.  13 ,  14 A- 14 B, and  15   . Additionally, examples of the disclosure can include measuring the concentration of a sample at different depths within the sample, which can lead to optical paths with different path lengths.  FIG.  16 A  illustrates a cross-sectional view of an exemplary system configured to measure a concentration and type of one or more substances located at different depths in a sample according to examples of the disclosure. In some examples, the one or more substances of interest can have a low concentration (e.g., more than one order of magnitude less) in the sample than other substances of interest. In some examples, the concentration of the one or more substances can lead to a low SNR (i.e., SNR&lt;10 −4  or 10 −5 ). System  1600  can be close to, touching, resting on, or attached to sample  1620 . Sample  1620  can include one or more locations, such as location  1657  and location  1659 , where the substance can be measured. Location  1657  can be located a depth  1661  away from the edge of the system, and location  1659  can be located a depth  1663  away from the edge of the system. In some examples, depth  1661  can be different from depth  1663 . 
     System  1600  can include light source  1602 . Light source  1602  can be configured to emit light  1650 . Light source  1602  can be any source capable of generating light including, but not limited to, a lamp, laser, LED, OLED, EL source, super-luminescent diode, super-continuum source, fiber-based source, or a combination of one or more of these sources. In some examples, light source  1602  can be capable of emitting a single wavelength of light. In some examples, light source  1602  can be capable of emitting a plurality of wavelengths of light. In some examples, light source  1602  can be any tunable source capable of generating a SWIR signature. System  1600  can include input region  1682  located close to or near sample  1620  or an edge of the system. Input region  1682  can be formed by one or more transparent components including, but not limited to, a window, optical shutter, or mechanical shutter. 
     Light  1650  can exit system  1600  through input region  1682 . Light that exits system  1600  and travels to location  1657  can be referred to as light  1652 . Light  1652  can have any angle of incidence at location  1657  including, but not limited to, 45°. In some examples, light  1650  can a collimated beam. Location  1657  can include a concentration of the substance of interest. Light  1652  can be partially absorbed at location  1657  and can be partially reflected as light  1654 . In some examples, light  1654  can be formed by light transmitting through the sample. Light  1654  can penetrate through sample  1620  and can enter system  1600  at location  1613  of optics  1610 . In some examples, optics  1610  can be in contact or near sample  1620 . Optics  1610  can be any type of optical component capable of changing the behavior and properties of the incoming light. Optics  1610  can include a plurality of locations, including location  1613  and  1617 , where light is allowed to enter. In some examples, optics  1610  can include a transparent material. In some examples, optics  1610  can be a Fresnel lens or a lens configured with a large aperture (e.g., an aperture larger than the size of the incoming light beam) and a short focal length. In some examples, optics  1610  can be a Silicon lens. 
     System  1600  can include optics, such as a confocal system. A confocal system can be any type of optical system configured for resolving path lengths, angles of incidence, exit locations, or any combination of these properties of multiple optical paths within a sample. In some examples, the optical system configured for accepting one or more incident light rays with a path length within a range of path lengths and an angle of incidence within a range of angles, and rejecting optical paths with a path length outside the range of path lengths and with an angle of incidence outside the range of angles. A confocal system can include optics  1616  and optics  1618 . Optics  1616  and optics  1618  can be objective lenses. An objective lens can be a lens capable of collecting the incident light and magnifying the light beam, while having a short focal length. Optics  1616  can collect light  1654  and direct light  1654  towards an aperture included in aperture  1686 . Aperture  1686  can include one or more apertures, such as opening  1685 , configured to allow light to transmit through. Aperture  1686  can be capable of selecting light with one or more specific path lengths, angles of incidence, or both and rejecting or attenuating light with other path lengths or angles of incidence. Selection and rejection of light based on path length, angle of incidence, or both can be optimized by adjusting the aperture size (i.e., the size of the aperture in the aperture plane). The selected light (i.e., light with one or more specific path lengths, angles of incidence, or both) can be in focus when it reaches an aperture in the aperture plane, and rejected light can be out of focus. Light that is out of focus can have a beam size that is larger than the aperture size, can have an angle of incidence that is outside the collection range, or both, and therefore can be rejected. Light that is in focus can have a light beam that is within a range of path lengths and range of collection angles, and therefore can be allowed to transmit through the aperture plane. In some examples, the system can include one or more modulating elements, such as micromirrors, acousto-optic modulators, or electro-optic modulators. 
     Light  1654  exiting opening  1685  can transmit through optics  1618  and can be incident on microoptics  1623 , included in microoptics unit  1629 . Microoptics unit  1629  can comprise a plurality of microlenses, such as microoptics  1623  and microoptics  1627 , attached to a substrate. A microlens can be a small lens or one that is smaller (e.g., a lens with a diameter less than 1 mm) than a conventional lens. In some examples, the microlenses can be any type of lens and can include any type of material conventionally used in lenses. In some examples, two or more of the microlenses can have the same optical and/or physical properties. One skilled in the art would appreciate that the same optical properties and the same physical properties can include tolerances that result in a 15% deviation. Light  1654  can transmit through microoptics  1623  and can be incident on detector pixel  1633 . In some examples, microoptics unit  1629  can be coupled to one or more aperture planes. In some examples, microoptics unit  1629  can be coupled to a patterned aperture, such as an aperture where locations between adjacent microoptics are opaque to prevent light mixing. 
     Detector pixel  1633  can be included in detector array  1630 . Detector array  1630  can include a plurality of detector pixels, such as detector pixel  1633  and  1637 . In some examples, detector array  1630  can be a single detector pixel detector. In some examples, at least one detector pixel can be independently controlled from other detector pixels included in detector array  1630 . In some examples, at least one detector pixel can be capable of detecting light in the SWIR. In some examples, at least one detector pixel can be a SWIR detector capable of operating between 2.2-2.7 μm. In some examples, at least one detector pixel can be a HgCdTe, InSb, or InGaAs based detector. In some examples, at least one detector pixel can be capable of detecting a path length, angle of incident, and/or exit location of the incoming light beam. Detector pixel  1633  can detect light  1654  and can generate an electrical signal indicative of the properties of light  1654 . Detector array  1630  can transmit the electrical signal to controller  1640 . Controller  1640  can process and/or store the electrical signal. 
     System  1600  can determine the concentration and type of substance in sample  1620  by utilizing the information from light traveling through the sample in conjunction with the information from light reflecting off reflector  1622 . Light source  1602  can emit light  1664 , which can reflect off reflector  1622 . Reflector  1622  can include any type of material capable of at least partially reflecting light. Exemplary reflective materials can include, but are not limited to, Ti, Co, Nb, W, NiCr, TiW, Cr, Al, Au, and Ag. The thickness of reflector  1622  can be determined based on the wavelength of light, type of material, and/or composition. In some examples, the size and shape of reflector  1622  can be configured to be larger or the same size and/or shape of the light beam included in light  1664 . One skilled in the art would appreciate that the same size and the same shape can include tolerances that result in a 15% deviation. In some examples, reflector  1622  can be configured to reflect greater than 75% of light  1764 . In some examples, reflector  1622  can be configured to reflect greater than 90% of light  1764 . In some examples, the size and shape of reflector  1622  can be such that no or a minimal (e.g., less than 10%) amount of light  1664  is allowed to transmit through the reflector  1622 , and light  1664  is prevented from traveling through sample  1620 . In some examples, reflector  1622  can be configured to reflect light  1664  as a specular reflection. In some examples, reflector  1622  can be a spectroscopically neutral blocker. In some examples, the reference can be formed by chopping light  1664  between the sample  1620  and reference (e.g., reflector  1622 ). 
     Light  1664  can reflect off reflector  1622  towards optics  1616 . Light  1664  can transmit through optics  1616  towards aperture  1686 . In some examples, the path length of light  1664  can be a known value, so aperture  1686  can be configured to include opening  1689 , whose size and shape can allow light  1664  to transmit through. Light  1664  exiting aperture plane  1668  can be incident on optics  1618 . Light  1664  can transmit through optics  1618  and can be incident on optics  1619 . Optics  1619  can be any type of optics configured for spreading out the incoming light beam. In some examples, optics  1619  can be a negative lens, which can be a lens with a focal length that is negative. In some examples, optics  1619  can be a prism. In some examples, optics  1619  can include a different prism wedge angled for each detector pixel included in detector array  1630 . In some examples, system  1600  can be configured with a beamsplitter for spreading out the incoming light beam. In some examples, optics  1619  can be configured to spread out or divide light into multiple beams, such as light  1666  and light  1667 . In some examples, optics  1619  can spread out light such that each light beam is directed to a different detector pixel included in detector array  1630 . In some examples, optics  1619  can uniformly spread out light such that one or more optical properties of each light beam are the same. One skilled in the art would appreciate that the same optical properties can include tolerances that result in a 15% deviation. In some examples, optics  1619  can spread out the light beam such that intensities of at least two light beams are different. In some examples, optics  1619  can comprise multiple optics or microoptics. In some examples, the size and/or size of optics  1619  can be based on the number of detector pixels and/or the properties of the one or more light beams exiting optics  1619 . In some examples, an aperture can be coupled to optics  1619  to control the properties and/or direction of light exiting optics  1619 . In some examples, optics  1619  or system  1600  can be configured such that light that reflects off a surface of sample  1620  or an edge of system  1600  reflects back into the system (i.e., light that has not traveled through sample  1620 ) and is prevented from being incident on optics  1619 , although stray light or background light can be incident on optics  1619 . 
     Light  1664  can transmit through optics  1619  to form light  1666 . Light  1666  can be incident on detector pixel  1633 . Detector pixel  1633  can detect light  1666  and can generate an electrical signal indicative of the properties of light  1666 . Detector array  1630  can transmit the electrical signal controller  1640 . Controller  1640  can process and/or store the electrical signal. Controller  1640  can utilize the signal information measured from light  1654  to determine the reflectivity or concentration of the substance at location  1657  and can utilize the signal information from light  1666  to determine the properties of reflector  1622 . Using any of the above discussed methods, controller  1640  can process both signal information to determine the concentration and type of substance at location  1657 . 
     Similar to measuring the concentration and type of one or more substances at location  1657 , the same components can be used to measure the concentration and type of one or more substances at location  1659 . Light source  1602  can emit light  1650 , which can exit system  1600  at input region  1682  to form light  1653 . In some examples, system  1600  can include multiple apertures. For example, system  1600  can include at least two apertures, where light  1652  can exit one aperture and light  1653  can exit another aperture. Light  1653  can be incident on location  1659  and can reflect back into system  1600  as light  1655 . Light  1655  can enter system  1600  through optics  1610  at location  1617 . Light  1655  can transmit through optics  1616  and can be incident on aperture  1686 . Aperture  1686  can include opening  1687  configured to allow light  1655  (and any light with the same path length as light  1655 ) to transmit through. One skilled in the art would appreciate that the same path length can include tolerances that result in a 15% deviation. In some examples, since location  1657  can be located at depth  1661 , different from depth  1663  of location  1659 , aperture  1686  can include at least two apertures with different aperture sizes. For example, opening  1685  can be configured with an aperture size based on the path length of light  1654 , and opening  1687  can be configured with an aperture size based on the path length of light  1655 . Light  1655  can transmit through opening  1687 , can transmit through optics  1618 , and can be incident on microoptics  1627 . Light  1655  can transmit through microoptics  1627  and can be detected by detector pixel  1637 , included in detector array  1630 . Detector pixel  1637  can detect light  1655  and can generate an electrical signal indicative of the properties of light  1655 . Detector array  1630  can transmit the electrical signal can be transmitted to controller  1640 , and controller  1640  can process and/or store the electrical signal. 
     Controller  1640  can utilize the signal information measured from light  1655  to determine the reflectivity or concentration of the substance at location  1659  and can utilize the signal information from light  1667  to determine the properties of reflector  1622 . Controller  1640  can process both signal information to determine the concentration of the substance at location  1659 . In some examples, controller  1640  can determine the properties of reflector  1622  (or light  1666  incident on detector pixel  1633 ) and light  1667  incident on detector pixel  1637  simultaneously without the need for separate measurements. In some examples, location  1657  and location  1659  can have the same depth from a surface of the sample  1620 . One skilled in the art would appreciate that the same depth can include tolerances that result in a 15% deviation. In some examples, location  1657  and location  1659  can have different depths from the surface of the sample  1620 . Controller  1640  can measure the reflectivity, refractive index, density, concentration, scattering coefficient, scattering anisotropy, absorbance, or any combination of optical properties at both location  1657  and location  1659  and can average the measured values. Although the figure and discussion above relates to two locations in the sample, examples of the disclosure can include any number of locations and are not limited to one or two locations. 
     As illustrated in the figure, system  1600  can include a plurality of apertures, a plurality of microoptics, and a plurality of detector pixels, where each aperture and microoptics can be coupled to a detector pixel. In some examples, each aperture-microoptics-detector pixel trio can be associated with a location in the sample. In some examples, the association can be one aperture-microoptics-detector pixel trio to one location in the sample. For example, opening  1685 , microoptics  1623 , and detector pixel  1633  can be associated with location  1657 . Similarly, opening  1687 , microoptics  1627 , and detector pixel  1637  can be associated with location  1659 . Since controller  1640  can associate detector pixel  1633  and detector pixel  1637  to the different locations (e.g., location  1657  and location  1659 ) in sample  1620 , controller  1640  can determine and locate different concentrations of the substance for different locations within sample  1620 . In some examples, different substances can be located in the different locations and controller  1640  can associate the locations to the different substances. 
     In some examples, system  1600  can be polarization sensitive. For some samples, polarized light incident on the sample can reflect strongly off the surface of the sample without undergoing a significant change in polarization. In some examples, this reflected light can be largely specular. In contrast, polarized light that enters the sample and reflects off one or more layers can have an initial polarization when incident on the sample, but can become progressively depolarized by scattering from one or more substances in the sample. The degree of polarization can be used to determine the depth that light travels in the sample prior to backscattering. The depth that light travels in the sample prior to backscattering can be used to estimate the path length of the optical path. In some examples, the path length of the optical path can be equal to two times the scattering depth. In some examples, the degree of polarization of light that travels through the sample and reflects back can also provide information about the nature of the sample. 
     In some examples, system  1600  can be configured to measure the change in polarization state by including one or more polarizing filters. A first polarizing filter can be located between light source  1602  and sample  1620 , and a second polarizing filter can be located between sample  1620  and detector  1630 . In some examples, the second polarizing filter can be different from the first polarizing filter in that the second polarizing filter can be configured to block out polarized light with a polarization that the first polarizing filter transmits through. In such a manner, light reflected off the surface of sample  1620  can be spatially separated from reflected off a location in sample  1620 . 
       FIG.  16 B  illustrates a cross-sectional view of an exemplary polarization sensitive system according to examples of the disclosure. System  1601  can include one or more of the components included in system  1600 , discussed above and illustrated in  FIG.  16 A . System  1601  can further include beamsplitter  1606  and detector  1632 . Beamsplitter  1606  can split light  1655  into two light paths, one light path can be measured by detector pixel  1637  included in detector array  1630 , and the other light path can be measured by detector  1632 . Detector pixel  1637  can be configured to measure a different polarization than detector  1632 . For example, detector pixel  1637  can be configured to measure p-polarization, whereas detector  1632  can be configured to measure s-polarization. 
     In some examples, beamsplitter  1606  can be a polarizing beamsplitter. S-polarized light can reflect off a surface of beamsplitter  1606  and can be detected by detector  1632 . In some examples, detector  1632  can include a wire grid polarizer located on its surface. In some examples, detector  1630  can include a wire grid polarizer located on the surface. P-polarized light can transmit through beamsplitter  1606  and can be detected by detector pixel  1637 . Based on the ratio of s-polarized light (e.g., light detected by detector  1632 ) and p-polarized light (e.g., light detected by detector pixel  1637 ), the concentration and type of one or more substances in the sample can be determined. 
     In some examples, specular reflectance from light that has not traveled into the sample can be excluded or removed from the measurements by configuring light  1653  to have an angle of incidence at location  1659  different from the angle of the incidence of scattered light  1655  at location  1617 . In some examples, the specular reflectance can be discarded by directing light onto a black absorbing material (e.g., black mask). In some examples, system  1601  can include a polarizer located between location  1659  and detector pixel  1637 . The polarizer can be configured to exclude light having one or more polarizations. 
     In some examples, the amount of scattering can depend on the size of the scattering objects in the sample. As a result, the amount of scattering and the peak scattering angle can be a function of wavelength. For example, at 1.5-2.5 μm, a large percentage of light (e.g., greater than 30%) scattered from the sample can have a scattering angle between 40-60°. The scattering angle can be related to the size of one or more substances located in the sample. By associating the scattering angles with the size of one or more substances located in the sample, different types of substances in the sample can be identified and distinguished. In some examples, system  1601  can include a wide wavelength band (e.g., greater than 1200 nm spectral range) antireflective (AR) coating in order to detect light with a scattering angle between 40-60°. In some examples, system  1601  can include one or more masking materials to limit the range of scattering angles detected by the system  1601 . 
       FIG.  17    illustrates a cross-sectional view of an exemplary system configured to determine a concentration and type of one or more substances located within a sample according to examples of the disclosure. In some examples, the one or more substances of interest can have a low concentration (e.g., more than one order of magnitude less) in the sample than other substances of interest. In some examples, the concentration of the one or more substances can lead to a low SNR (i.e., SNR&lt;10 −4  or 10 −5 ). Sample  1720  can include one or more locations, such as location  1757  and location  1759 , where one or more substances can be measured. 
     System  1700  can be close to, touching, resting on, or attached to sample  1720 . In some examples, system  1700  can be a compact, portable electronic device. Compact, portable electronic devices can have stringent size requirements due to the increasing demand for smaller, thinner, and lighter design that are more user-friendly and aesthetically appealing. To implement the functionality of the above disclosed examples, system  1700  can include components such as light source  1702 , microoptics unit  1729 , detector array  1730 , and controller  1740 . One or more components or optics can be eliminated by integrating the features into other components or optics and by placing the integrated components closer to a surface of the sample or an edge of the system. 
     Light source  1702  can be configured to emit light  1752 . Light source  1702  can be any source capable of generating light including, but not limited to, a lamp, laser, LED, OLED, EL source, super-luminescent diode, super-continuum source, fiber-based source, or a combination of one or more of these sources. In some examples, light source  1702  can be capable of emitting a single wavelength of light. In some examples, light source  1702  can be capable of emitting a plurality of wavelengths of light. In some examples, light source  1702  can be any tunable source capable of generating a SWIR signature. Light source  1702  can include one or more components for emitting multiple light beams, such as light  1752  and light  1753 , directed at different apertures, such as input region  1782  and input region  1791 . Input region  1782  and input region  1791  can be located close to or near sample  1720  or an edge of the system  1700 . System  1700  can also include one or more apertures, such as input region  1782 , input region  1791 , output region  1793 , and output region  1795 , and each aperture can be comprise one or more transparent components including, but not limited to, a window, optical shutter, and mechanical shutter. 
     Light  1752  can exit system  1700  through input region  1782 . Light  1752  can penetrate through sample  1720  and can be incident on location  1757 . Light  1752  can have any angle of incidence at location  1757  including, but not limited to, 45°. In some examples, light  1752  can be a collimated beam. Location  1757  can include a concentration of the substance of interest. Light  1752  can be partially absorbed at location  1757  and can be partially reflected as light  1754 . In some examples, light  1754  can be formed by light transmitting through the sample. Light  1754  can penetrate through sample  1720  and can enter system  1700  through output region  1793 . 
     Light  1754  can be incident on microoptics  1723  of microoptics unit  1729 . Microoptics unit  1729  can comprise a plurality of microoptics, such as microoptics  1723  and  1727 , attached to a substrate. In some examples, the microoptics can be any type of lens and can include any type of material conventionally used in lenses. In some examples, two or more of the microoptics included in the microoptics unit  1729  can have the same optical and/or physical properties. One skilled in the art would appreciate that the same optical properties and the same physical properties can include tolerances that result in a 15% deviation. Light  1754  can transmit through microoptics  1723  and can be incident on detector pixel  1733  of detector array  1730 . In some examples, microoptics unit  1729  can be coupled to one or more apertures or apertures. In some examples, microoptics unit  1729  can be coupled to a patterned aperture, such as an aperture where locations between adjacent microoptics are opaque to prevent light mixing. 
     Detector pixel  1733  can be included in detector array  1730 . Detector array  1730  can include a plurality of detector pixels, such as detector pixels  1733  and  1737 . In some examples, detector array  1730  can be a single pixel detector. In some examples, at least one detector pixel can be independently controlled from other detector pixels in the detector array  1730 . In some examples, at least one detector pixel can be capable of detecting light in the SWIR. In some examples, at least one detector pixel can be a SWIR detector capable of operating between 2.2-2.7 μm. In some examples, at least one detector pixel can be a HgCdTe, InSb, or InGaAs based detector. In some examples, at least one detector pixel can be capable of detecting a position and/or angle of the incoming light beam. Detector pixel  1733  can detect light  1754  and can generate an electrical signal indicative of the properties of light  1754 . Detector array  1730  can transmit the electrical signal to controller  1740 , which can process and/or store the electrical signal. 
     Light source  1702  can also emit light  1764  to measure the optical properties of reflector  1722 . Reflector  1722  can comprise any type of material, such as Ti, Co, Nb, W, NiCr, TiW, Cr, Al, Au, and Ag, capable of partially reflecting or reflecting a large percentage of light. The thickness of reflector  1722  can be determined based on the wavelength of light, type of material, and/or composition. In some examples, the size and shape of reflector  1722  can be configured to be larger or the same size and/or shape of light  1764 . One skilled in the art would appreciate that the same size and the same shape can include tolerances that result in a 15% deviation. In some examples, the reflector  1722  can be configured to reflect greater than 75% of light. In some examples, the reflector  1722  can be configured to reflect greater than 90% of light. In some examples, the size and shape of reflector  1722  can be such that no or minimal (e.g., less than 10%) amounts of light  1764  is allowed to transmit through reflector  1722 , and light  1764  is prevented from penetrating through sample  1720 . In some examples, reflector  1722  can be configured to reflect light  1764  as a specular reflection. In some examples, reflector  1722  can be a spectroscopically neutral blocker. In some examples, the reference can be formed by chopping light  1764  between sample  1720 ) and the reference (e.g., reflector  1722 ). 
     Light  1764  can reflect off reflector  1722  towards optics  1719 . Optics  1719  can be any type of optics configured for spreading out the incoming light beam. In some examples, optics  1719  can be a negative lens, which can be a lens with a focal length that is negative. In some examples, optics  1719  can be a prism. In some examples, optics  1719  can include a different prism wedge angled for each detector pixel included in the detector array  1730 . In some examples, system  1700  can be configured with a beamsplitter for spreading out the incoming light beam. In some examples, optics  1719  can be configured to spread out or divide light into multiple beams, such as light  1766  and  1767 . In some examples, optics  1719  can spread out light such that each light beam is directed to a different detector pixel included in the detector array  1730 . In some examples, optics  1719  can uniformly spread out light such that each light beam has one or more optical properties that are the same. One skilled in the art would appreciate that the same optical properties can include tolerances that result in a 15% deviation. In some examples, optics  1719  can spread out the light beam such that intensities of at least two light beams are different. In some examples, optics  1719  can comprise multiple optics or microoptics. In some examples, the size and/or size of optics  1719  can be based on the number of detector pixels and/or the properties of the one or more light beams exiting optics  1719 . In some examples, an aperture can be coupled to optics  1719  to control the properties and/or direct light exiting optics  1719 . In some examples, optics  1719  or system  1700  can be configured such that light that reflects off a surface of sample  1720  or an edge of system  1700  reflects back into the system (i.e., light that has not traveled through sample  1720 ) and is prevented from being incident on optics  1719 , although stray light or background light can be incident on optics  1719 . 
     Light  1764  can transmit through optics  1719  to form light  1766 . Light  1766  can be incident on detector pixel  1733 . Detector pixel  1733  can detect light  1766  and can generate an electrical signal indicative of the properties of light  1766 . Detector array  1730  can transmit the electrical signal to controller  1740 , which can process and/or store the electrical signal. Controller  1740  can utilize the signal information measured from light  1754  to determine the reflectivity or concentration of the substance at location  1757  and can utilize the signal information from light  1766  to determine the properties of reflector  1722 . Using any of the above discussed methods, controller  1740  can process both signal information to determine the concentration of the substance at location  1757 . 
     Similar to measuring the concentration of the substance at location  1757 , the same components can be used to measure the concentration of the substance at location  1759 . Light source  1702  can emit light  1753 , which can exit system  1700  at input region  1791 . Light  1753  can be incident on location  1759  and can reflect back into system  1700  as light  1755 . Light  1755  can enter system  1700  at output region  1795 . Light  1755  can be incident on microoptics  1727 , included in microoptics unit  1729 . Light  1755  can transmit through microoptics  1727  and can be incident on detector pixel  1737 , included in detector array  1730 . Detector pixel  1737  can detect light  1755  and can generate an electrical signal indicative of the properties of light  1755 . Detector array  1730  can transmit the electrical signal to controller  1740 , which can process and/or store the electrical signal. Controller  1740  can utilize the signal information measured from light  1755  to determine the reflectivity or concentration of the substance at location  1759  and can utilize the signal information from light  1767  to determine the properties of reflector  1722 . Controller  1740  can process both signal information to determine the concentration of the substance at location  1759  located in sample  1720 . In some examples, controller  1740  can determine the properties of reflector  1722  (or light  1766  incident on detector pixel  1733 ) and light  1767  incident on detector pixel  1737  simultaneously without the need for separate measurements. Controller  1740  can measure the reflectivity, refractive index, density, concentration, scattering coefficient, scattering anisotropy, absorbance, or a combination of these optical properties at both location  1757  and location  1759  and can average the measured values. Although the figure and discussion above relates to two locations in the sample, examples of the disclosure can include any number of locations and are not limited to one or two locations. 
     As illustrated in the figure, system  1700  can include a plurality of microoptics and a plurality of detector pixels, where each microoptics can be coupled to a detector pixel. Each microoptics-detector pixel pair can be associated with a location in the sample. In some examples, the association can be one microoptics-detector pixel pair to one location in the sample. For example, microoptics  1723  and detector pixel  1733  can be associated with location  1757 . Microoptics  1727  and detector pixel  1737  can be associated with location  1759 . Since controller  1750  can associate detector pixel  1733  and detector pixel  1737  to the different locations (e.g., location  1757  and location  1759 ) within the sample, controller  1750  can determine and locate different concentrations of the substance for different locations in sample  1720 . 
       FIG.  18    illustrates a top view of an exemplary system configured to measure one or more substances located within a sample according to examples of the disclosure. System  1800  can be close to, touching, resting on, or attached to the sample. System  1800  can be segmented into a plurality of units  1899 . Each unit  1899  can comprise one or more reflectors  1822  and a plurality of apertures  1882 . Reflector  1822  can include any type of material capable of at least partially reflecting light. In some examples, reflector  1822  may not be visible from the top view, but can be placed in the same location as indicated by the figure. 
     One or more of the plurality of apertures  1882  can be configured to allow light to enter or exit the top surface of system  1800 . One or more optical components, such as a light source, lens, microlens, detector pixel, or detector array, can be located close to, below, or above one or more of the plurality of apertures  1882 . In some examples, apertures  1882  and/or reflector  1822  can be circular in shape or can be a metal dot. In some examples, apertures  1882  and reflector  1822  can be separated by a gap or an optical isolation material to prevent light mixing. Although the figure illustrates the plurality of apertures  1882  as arranged in a column and row format with reflector  1822  located on one side of unit  1899 , the plurality of apertures  1882  can be arranged in any manner. For example, reflector  1822  can be located in the center and can be associated with surrounding apertures  1882  and corresponding components. In some examples, reflector  1822  can be associated with those optical components located in the same unit  1899 . For example, the reference measurement from reflector  1822  can be distributed by a negative lens (or prism or beamsplitter) to the optical components in the same unit  1899 . In some examples, each input or output region  1882  can be associated with a lens or microlens. The size and/or shape of the input or output region  1882  or lens or both can be based on location of the associated detector pixel in a detector array. In some examples, each input or output region  1882  can be associated with a depth below the surface of the sample and/or the angle of incidence of incoming light. 
     In some examples, due to the small size of the apertures, any of the above disclosed systems can include on 10-100 apertures and reflectors. For example, each aperture can have a diameter of 100-900 μm, and each unit can have a length (or width) of around 5 mm With a large number of apertures and reflectors, the system can measure a plurality of locations within the sample. In some examples, a plurality of apertures can be configured to measure locations with the same depth, and the controller can have a sufficient number of values to average to account for the inhomogeneity that can exist along different locations within the sample. One skilled in the art would appreciate that the same depth can include tolerances that result in a 15% deviation. In some examples, a plurality of apertures can be configured to measure locations with differing depths, and the system can account for inhomogeneity that can exist along the depth of sample. In some examples, a first set of apertures can be configured to measure a first substance, and a second set of apertures can be configured to measure a second substance different from the first substance. 
       FIG.  19    illustrates a top view of an exemplary system configured to measure a concentration and type of one or more substances located within a sample according to examples of the disclosure. System  1900  can be close to, touching, resting on, or attached to the sample. System  1900  can be segmented into a plurality of units  1999 . Each unit  1999  can comprise one or more reflectors  1922  and a plurality of input or output regions  1982 . Reflector  1922  can include any type of material capable of at least partially reflecting light. In some examples, reflector  1922  may not be visible from the top view, but can be placed in the same location as indicated by the figure. One skilled in the art would appreciate that the same location can include tolerances that result in a 15% deviation. 
     One or more of the plurality of input or output regions  1982  can be configured to allow light to enter or exit the top surface of system  1900 . One or more optical components, such as a light source, lens, microlens, detector, or detector array, can be located close to, below, or above one or more of the plurality of input or output regions  1982 . System  1900  can have the same components as system  1800 , but arranged as a grid of squares. In some examples, input or output regions  1982  and reflector  1922  can be separated by a gap or an optical isolation material to prevent light mixing. In some examples, reflector  1922  can be associated with input or output regions  1982  and corresponding optical components within the same unit  1999 . 
     Although some of the examples described and illustrated above were discussed separately, one skilled in the art would understand that one or more of the examples can be combined and included into a single system and/or method. For example, although system  1500  (illustrated in  FIG.  15   ) includes light blocker  1592  and system  1600  (illustrated in  FIGS.  16 A- 16 B ) includes aperture  1686 , both examples can be combined and included in a single system. 
     One or more of the functions described above can be performed, for example, by firmware stored in memory and executed by a processor or controller. The firmware can also be stored and/or transported within any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “non-transitory computer-readable storage medium” can be any medium (excluding a signal) that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The non-transitory computer readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such as a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks and the like. In the context of this document, a “transport medium” can be any medium that can communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, or infrared wired or wireless propagation medium. 
     As discussed above, examples of the disclosure can include measuring a concentration of a substance in a sample at a sampling interface. In some examples, the sample can include at a least a portion of a user, where additional information can be used to improve the delivery of measured information, analysis, or any other content that may be of interest to the users. In some examples, the measured information, analysis, or other content may include personal information such as information that can uniquely identify the user (e.g., can be used to contact or locate the user). In some examples, personal information can include geographic information, demographic information, telephone numbers, email addresses, mailing addresses, home addresses, or other identifying information. Use of such personal information can be used to the benefit of the user. For example, the personal information can be used to deliver the measured information, analysis, or other content to the user. Use of personal information can include, but is not limited to, enabling timely and controlled delivery of the measured information. 
     The disclosure also contemplates that an entity that may be measuring, collecting, analyzing, disclosing, transferring, and/or storing the personal information will comply with well-established privacy policies and/or practices. These privacy policies and/or practices can be generally recognized as meeting (or exceeding) industry or governmental requirements for private and secure personal information and should be implemented and consistently used. For example, personal information should be collected for legitimate and reasonable purposes (e.g., to deliver the measured information to the user) and should not be shared (e.g., sold) outside of those purposes. Furthermore, collected personal information should occur only after receiving the informed consent of the user(s). To adhere to privacy policies and/or practices, entities should take any steps necessary for safeguarding and securing outside access to the personal information. In some examples, entities can subject themselves to third party evaluation(s) to certify that the entities are adhering to the well-established, generally recognized privacy policies and/or practices. 
     In some examples, the user(s) can selectively block or restrict access to and/or use of the personal information. The measurement system can include one or more hardware components and/or one or more software applications to allow the user(s) to selective block or restrict access to and/or use of the personal information. For example, the measuring system can be configured to allow users to “opt in” or “opt out” of advertisement delivery services when collecting personal information during registration. In some examples, a user can select which information (e.g., geographical location) to provide and which information (e.g., phone number) to exclude. 
     Although examples of the disclosure can include systems and method for measuring a concentration of a substance with the use of the user&#39;s personal information, examples of the disclosure can also be capable of one or more functionalities and operation without the user&#39;s personal information. Lack of all or a portion of the personal information may not render the systems and methods inoperable. In some examples, content can be selected and/or delivered to the user based on non-user specific personal (e.g., publicly available) information. 
     In some examples, a system for measuring a concentration of a substance in a sample at a sampling interface is disclosed. The system may comprise: a light source configured to emit a first light including one or more wavelengths; one or more optics; one or more modulators configured to modulate at least a portion of the first light, the one or more modulators located between the one or more optics and the sampling interface; a reference comprising one or more spectroscopic properties; a first detector configured to detect the at least portion of the first light; and logic configured to: send one or more first signals to the light source, and receive one or more second signals from the first detector. Additionally or alternatively to one or more examples disclosed above, in some examples, the one or more modulators includes an optical chopper located between the light source and the sampling interface or reference. Additionally or alternatively to one or more examples disclosed above, in some examples, the reference is at least one of a neutral density filter, blank attenuator, and a reflector. Additionally or alternatively to one or more examples disclosed above, in some examples, the reference is a reflector made of at least one of Titanium (Ti), Cobalt (Co), Niobium (Nb), Tungsten (W), Nickel Chrome (NiCr), Titanium Tungsten (TiW), Chrome (Cr), Aluminum (Al), Gold (Au), and Silver (Ag). Additionally or alternatively to one or more examples disclosed above, in some examples, the reference is a reflector configured with a size that is greater than or equal to a size of the first light emitted from the light source. Additionally or alternatively to one or more examples disclosed above, in some examples, the reference is a reflector that includes a metal dot. Additionally or alternatively to one or more examples disclosed above, in some examples, the reference is a specular reflector. Additionally or alternatively to one or more examples disclosed above, in some examples, the reference is a reflector and a portion of the first light is incident on the reflector. Additionally or alternatively to one or more examples disclosed above, in some examples, the system further comprises a filter, the filter including at least one of an acousto-optic tunable filter (AOTF), angle tunable narrow bandpass filter, or a plurality of sub-filters, each sub-filter having a different spectral range, located between the light source and the beamsplitter, the filter configured to select one or more discrete wavelengths from the one or more wavelengths of the first light emitted from the light source. Additionally or alternatively to one or more examples disclosed above, in some examples, an edge of the system is located at a sample-system interface, and further wherein the one or more optics includes a silicon objective lens, the silicon objective lens configured to collect a reflection of at least a portion of the first light at the sample-system interface. Additionally or alternatively to one or more examples disclosed above, in some examples, the first detector includes a plurality of detector pixels, and further wherein the one or more optics includes a optics configured for distributing a portion of the first light to one or more of the plurality of detector pixels. Additionally or alternatively to one or more examples disclosed above, in some examples, the first optics is at least one of a negative lens, prism, and beamsplitter. Additionally or alternatively to one or more examples disclosed above, in some examples, distributing the portion of the first light comprises splitting the portion of the first light into multiple light beams, each light beam directed to a different detector pixel included a set of the plurality of detector pixels. Additionally or alternatively to one or more examples disclosed above, in some examples, each detector pixel of the set of the plurality of detector pixels is associated with different locations in the sample, each location having a same path length within the sample. Additionally or alternatively to one or more examples disclosed above, in some examples, each detector pixel included in the set of plurality of detector pixels is associated with different path lengths in the sample. Additionally or alternatively to one or more examples disclosed above, in some examples, distributing a portion of the first light comprises splitting the portion of the first light into multiple light beams, at least one of the multiple light beams configured to have one or more properties that is same as another of the multiple light beams. Additionally or alternatively to one or more examples disclosed above, in some examples, the one or more optics includes a microoptics unit, the microoptics unit comprising a plurality of microlenses. Additionally or alternatively to one or more examples disclosed above, in some examples, the sample comprises a plurality of locations, and further wherein the first detector comprises a plurality of detector pixels, each detector pixel associated with one of the plurality of microoptics and one of the plurality of locations. Additionally or alternatively to one or more examples disclosed above, in some examples, the first detector is configured to measure short-wave infrared (SWIR) in at least a portion of 1.4-2.7 μm. Additionally or alternatively to one or more examples disclosed above, in some examples, the first detector is configured to measure short-wave infrared (SWIR) in at least a portion of 2.2-2.7 μm. Additionally or alternatively to one or more examples disclosed above, in some examples, the first detector is a HgCdTe, InSb, or InGaAs based detector. Additionally or alternatively to one or more examples disclosed above, in some examples, the system further comprises a light blocking material capable of absorbing or blocking light reflected from an edge of the system. Additionally or alternatively to one or more examples disclosed above, in some examples, the logic is further configured to: determine whether the received one or more second signals match a spectral fingerprint of the substance; and determine the concentration of the substance at the sampling interface based on the match of the spectral fingerprint. Additionally or alternatively to one or more examples disclosed above, in some examples, the one or more optics includes a beamsplitter configured to split at least a portion of the first light emitted from the light source into multiple beams comprising at least a second light and a third light. Additionally or alternatively to one or more examples disclosed above, in some examples, the system further comprises a second detector configured to detect a first polarization of the third light, wherein the first detector is configured to detect a second polarization of the second light, the second polarization being different than the first polarization. 
     In some examples, a system for projecting a first image is disclosed. The system comprising: one or more optics configured to reimage the first image located on a first plane to a second image located on a second plane, different from the first plane, at least one of the one or more optics producing an intermediate plane of focus located between the first plane and the second plane, wherein the first image includes a plurality of concentration values. Additionally or alternatively to one or more examples disclosed above, in some examples, the second image includes a magnification of the first image. Additionally or alternatively to one or more examples disclosed above, in some examples, the one or more optics is capable of selecting a first light with a same path length as a pre-determined path length or within a range of pre-determined path lengths and rejecting a second light with path length different from the pre-determined path length or outside the range of pre-determined path lengths. Additionally or alternatively to one or more examples disclosed above, in some examples, the system further comprises an aperture, the aperture comprising one or more aperture, each aperture configured to select the fourth light and reject the fifth light. Additionally or alternatively to one or more examples disclosed above, in some examples, the aperture comprises at least two apertures of different sizes. 
     In some examples, a method for measuring a concentration of a substance in a sample at a sampling interface, the method comprising: during a calibration phase: deactivating a light source and a modulator, determining a level by detecting with a detector an amount of dark current or stray light or both, and setting a zero level equal to the level; and during a measurement phase: measuring an absorbance, reflectance, or transmittance value in a same location of the sampling interface to determine an optical value; measuring an absorbance, reflectance, or transmittance value in a reference to determine a reference optical value, and dividing the optical value by the reference optical value to obtain a sampling point, repeating the determination of the optical value and the determination of the reference optical value to obtain a plurality of sampling points, and averaging the plurality of sampling points to determine the concentration of the substance at the sampling interface, wherein the number of plurality of sampling points within a continuous measurement phase is less than 100. Additionally or alternatively to one or more examples disclosed above, in some examples, the number of plurality of sampling points is less than or equal to 10. Additionally or alternatively to one or more examples disclosed above, in some examples, the method further comprises a plurality of frames, each frame include one calibration phase and one measurement phase, and wherein determining the concentration of the substance at the sampling interface comprising averaging the plurality of sampling points from at least two of the plurality of frames. Additionally or alternatively to one or more examples disclosed above, in some examples, a duration of the measurement phase is based on a stability of at least one of the laser and the detector. Additionally or alternatively to one or more examples disclosed above, in some examples, the duration of the measurement phase is less than 60 seconds. Additionally or alternatively to one or more examples disclosed above, in some examples, the method is capable of accounting for zero drift and gain drift from both the light source and the detector. Additionally or alternatively to one or more examples disclosed above, in some examples, the method is capable of removing stray light. Additionally or alternatively to one or more examples disclosed above, in some examples, determining the reference optical value comprises modulating light between the sample and the reference. Additionally or alternatively to one or more examples disclosed above, in some examples, the measurement phase includes a plurality of optical values and a plurality of reference optical values, and further wherein the plurality of optical values and the plurality of reference optical values are measured at different times within the measurement phase. 
     Although the disclosed examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosed examples as defined by the appended claims.

Metadata:
Filing Date: 20201005
Publication Date: 20230221
Grant Date: 20230221
Priority Date: 20150901
Inventors: KANGAS, Miikka M.
ARBORE, Mark Alan
SIMON, DAVID I.
BISHOP, MICHAEL J.
HILLENDAHL, JAMES W.
CHEN, ROBERT
Assignee: APPLE INC
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Family ID: 56853926