Patent Publication Number: US-2021187668-A1

Title: Systems and methods for formation of continuous channels within transparent materials

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/951,473, filed on Dec. 20, 2019, entitled “Systems And Methods For Formation Of Continuous Channels Within Transparent Materials,” the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND 
     Plastic microfluidic chips can be produced using fabrication processes which produce two dimensional structures in thermoplastic materials using methods such as hot embossing, injection molding, or casting. These structures may include multiple narrow channels and other features which may be closely spaced. An example of a chip which was designed to collect circulating tumor cells from whole blood is shown in  FIGS. 1A-B . The chip has ˜1.5 million microfabricated features with characteristic widths between 12 μm-50 μm. The structures are produced in thin layers which are bonded together to form a sandwich as illustrated in  FIG. 2 . The bond must seal the layers together while keeping individual structures separate. 
     Microfluidic chips can be produced through photolithographic techniques and the resulting tooling (like that for the chip shown in  FIGS. 1A-B ) can be very complex, expensive, and time consuming to produce. The need for complex tooling can increase financial costs in production phases and time costs in prototyping and design phases. 
     Ports between individual layers in the microfluidic chip can be drilled before the individual layers are consolidated and bonded together. This can limit current microfluidic chip design to 2-dimensional (2D) patterns. 
     Bonding (or lidding) different layers of the microfluid chip together can be difficult. Bonding can be done with a combination of solvent, heat and pressure. As a result of the complexities of the bonding process, an intended seal between multiple adjacent features can fail. For example, the intended seal can fail due to leaks between structures or due to fused structures that prevent free flow. 
     As a result, producing microfluidic chips can be time consuming, expensive and can exhibits a low yield. For the above reasons, improved methods and systems for producing microfluidic chips are sought. 
     SUMMARY 
     An embodiment of a method for forming a continuous channel in a transparent material includes: generating, using a laser source, a laser beam; converging, using a focus optic, the laser beam to a focal region outside of a transparent material; moving the focal region from outside the transparent material to inside the transparent material along a first scan path; and, forming a continuous channel within the transparent material generally along the first scan path, wherein the continuous channel has a vent to outside of the transparent material located at least at one end. 
     In some embodiments, the method also includes moving the focal region from inside the transparent material to outside the transparent material along a continuation of the first scan path; and elongating the continuous channel within the transparent material generally along the continuation of the first scan path, such that the continuous channel has a vent to outside the transparent material at least two ends. 
     In some embodiments, the method also includes moving the focal region along a second scan path that is substantially parallel to and separated by a separation distance from the first scan path, wherein the separation distance is based upon a width of the focal region; and, widening a width of the continuous channel. In some versions, the separation distance is substantially along one or more of 3 mutually orthogonal axes: a lateral (X) axis, a horizontal (Y) axis, and a vertical (Z) axis. In some versions, the separation distance is between about 1 and 100 micrometers. 
     In some embodiments of the method, the method also includes removing ablation product from within the continuous channel. In some versions, removing ablation product includes using a solution, wherein the solution has a pH that is complementary or neutral to a pH of the ablation product. In some versions, removing ablation product from within the continuous channels includes using an ultrasonic cleaner. 
     In some embodiments of the method, the method also includes pulsing the laser source and the laser beam has a pulse repetition rate of at least about  1 kHz. In some versions, the laser beam has a pulse duration no greater than about 1 nanosecond. 
     In some embodiments of the method, the transparent material comprises at least one of: General Purpose Polystyrene (GPPS), Methylmethacrylate Acrylonitrile Butadiene Styrene (MABS), Styrene acrylonitrile (SAN), Styrene Methyl Methacrylate (SIVIMA), Methacrylate Butadiene Styrene (MBS), Styrene-butadiene (SB) Copolymer, Polycarbonate (PC), High Heat Polycarbonate (HH PC), Polyethylene Terephthalate (PET), Glycol-Modified Polyethylene Terephthalate (PET-G), Poly(Methyl Methacrylate) (PMMA), Polyethyleneimine (PEI), Polyethersulfone (PES), Polysulfone (PSU), Polypropylene Homopolymer (PP H), Random Copolymerized Polypropylene (PP R), Low-Density Polyethylene (LDPE), Polylactic Acid (PLA), glass, Styrene-Ethylene/Butylene-Styrene (SEBS), Thermoplastic Polyurethane (TPU), Thermoplastic Olefin (TPO), crystal, sapphire, and quartz. 
     In some embodiments of the method, converging the laser beam is done at a numerical aperture (NA) of at least about 0.3. 
     In some embodiments of the method, the laser beam has a wavelength in a range between about 400 and 4000 nanometers. 
     In some embodiments of the method, the method additionally includes introducing a vacuum to the continuous channel by way of one or more vents. 
     In some embodiments of the method, the scan path at a first surface of the transparent material is generally normal to the first surface of the transparent material. 
     An embodiment of a system for forming a continuous channel in a transparent material includes: a laser source, a focus optic, one or more translation stages, and a controller. The laser source is configured to generate a laser beam. The focus optic is configured to converge the laser beam to a focal region that is initially located outside of the transparent material. The one or more translation stages are configured to move the focal region from outside the transparent material to inside the transparent material along a first scan path, either by moving the material relative to the stationary laser focal region or by moving the laser focal region relative to the stationary material or some combination of the two. And, the controller is configured to control at least one of the laser source and the one or more translation stages to form a continuous channel within the transparent material generally along the first scan path, wherein the continuous channel has a vent to outside the transparent material located at least at one end. 
     In some embodiments of the system, the controller is further configured to control the at least one translation stage to move the focal region from inside the transparent material to outside the transparent material along a continuation of the first scan path to elongate the continuous channel within the transparent material generally along the continuation of the first scan path, such that the continuous channel has a vent to outside the transparent material at least at two ends. 
     In some embodiments of the system, the controller is further configured to control the at least one translation stage to move the focal region along a second scan path that is substantially parallel to and separated by a separation distance from the first scan path to widen a width of the continuous channel, wherein the separation distance is based upon a width of the focal region. In some versions, the separation distance is substantially along one or more of 3 mutually orthogonal axes, including: a lateral axis (X), a horizontal axis (Y), and a vertical axis (Z). In some versions, the separation distance is between about  1  and  100  micrometers. 
     In some embodiments of the system, the system additionally includes an ablation product removal system that is configured to remove an ablation product from within the continuous channel. In some versions, the ablation product removal system includes a solution; wherein, the solution has a pH that is complementary or neutral to a pH of the ablation product. In some versions, the ablation product removal system comprises an ultrasonic cleaner. 
     In some embodiments of the system, the laser beam is pulsed at a repetition rate of at least about 1 KHZ. In some versions, the laser beam has a pulse duration that is no greater than about 1 nanosecond. 
     In some embodiments of the system, the transparent material includes at least one of: General Purpose Polystyrene (GPPS), Methylmethacrylate Acrylonitrile Butadiene Styrene (MABS), Styrene acrylonitrile (SAN), Styrene Methyl Methacrylate (SMIMA), Methacrylate Butadiene Styrene (MBS), Styrene-butadiene (SB) Copolymer, Polycarbonate (PC), High Heat Polycarbonate (HH PC), Polyethylene Terephthalate (PET), Glycol-Modified Polyethylene Terephthalate (PET-G), Poly(Methyl Methacrylate) (PMMA), Polyethyleneimine (PEI), Polyethersulfone (PES), Polysulfone (PSU), Polypropylene Homopolymer (PP H), Random Copolymerized Polypropylene (PP R), Low-Density Polyethylene (LDPE), Polylactic Acid (PLA), glass, Styrene-Ethylene/Butylene-Styrene (SEBS), Thermoplastic Polyurethane (TPU), Thermoplastic Olefin (TPO), crystal, sapphire, and quartz. 
     In some embodiments of the system, wherein the focus optic is further configured to converge the laser beam at a numerical aperture of at least about 0.3. 
     In some embodiments of the system, the laser beam has a wavelength in a range of between about 400 and 4000 nanometers. 
     In some embodiments of the system, the system additionally includes a vacuum system, configured to introduce a vacuum to the continuous channel by way of one or more vents. 
     In some embodiments of the system, the scan path at a first surface of the transparent material is generally normal to the first surface of the transparent material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the disclosure will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1A  displays a state-of-the-art macroscopic view of a microfluidic chip; 
         FIG. 1B  displays multiple microscopic views of the microfluidic chip of  FIG. 1A ; 
         FIG. 2  illustrates a state-of-the-art bonding process for microfluidic chips; 
         FIG. 3A  shows a flow chart for a method of forming microfluidic channels in a transparent material, according to some embodiments; 
         FIG. 3B  illustrates formation of a continuous channel with multiple scan paths, according to some embodiments; 
         FIG. 3C  schematically illustrates a unidirectional scanning arrangement, according to some embodiments; 
         FIG. 3D  schematically illustrates a first bidirectional scanning arrangement, according to some embodiments; 
         FIG. 3E  schematically illustrates a second bidirectional scanning arrangement, according to some embodiments; 
         FIG. 4  schematically represents a system for forming microfluidic channels in a transparent material, according to some embodiments; 
         FIG. 5A  schematically illustrates transparent material blanks for forming a continuous channel within, according to some embodiments; 
         FIG. 5B  schematically represents a process for forming a continuous channel in a transparent material blank having preformed ports, according to some embodiments; 
         FIG. 6A  schematically represents a process for forming a continuous channel in a transparent material, which includes a vacuum, according to some embodiments; 
         FIG. 6B  schematically represents a process for forming a continuous channel in a transparent material, which includes a vacuum, according to some embodiments; 
         FIG. 6C  schematically represents an isometric view of a process for forming a continuous channel in a transparent material, according to some embodiments; 
         FIG. 6D  schematically represents a front view of a process for forming a continuous channel in a transparent material, according to some embodiments; 
         FIG. 7  is an image showing a system for forming continuous channels in a transparent material, according to some embodiments; 
         FIG. 8  is an image that shows air passing through a continuous channel formed within a transparent material, according to some embodiments; 
         FIG. 9A  is a scanning electron microscope (SEM) of a surface of a modified transparent material with a scan path separation distance of two micrometers, according to some embodiments; 
         FIG. 9B  is a scanning electron microscope (SEM) of a surface of a modified transparent material with a scan path separation distance of five micrometers, according to some embodiments; 
         FIG. 9C  is a scanning electron microscope (SEM) of a surface of a modified transparent material with a scan path separation distance of seven micrometers, according to some embodiments; 
         FIG. 9D  is a scanning electron microscope (SEM) of a surface of a modified transparent material with a scan path separation distance of ten micrometers, according to some embodiments; 
         FIG. 10  is an image showing channels with differing lengths formed in a transparent material, according to some embodiments; 
         FIG. 11  is an image showing channels at different depths formed in a transparent material, according to some embodiments; and, 
         FIG. 12  is an image showing a functional microfluidic device in a transparent material, manufactured according to some embodiments. 
     
    
    
     It is noted that the drawings are not necessarily to scale. The drawings are intended to depict only typical aspects of the subject matter disclosed herein, and therefore should not be considered as limiting the scope of the disclosure. The systems, devices, and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments. 
     DETAILED DESCRIPTION 
     As described above  FIGS. 1A-B  represent a microfluidic chip  100  produced using state-of-the-art methods. Specifically, this microfluidic chip  100  is a multi-stage CTC iChip developed by Massachusetts General Hospital. The CTC iChip  100  has approximately 1.5 million microfabricated features (12 μm-50 μm). The CTC iChip  100  is designed to separate circulating tumor cells from whole blood. 
     Referring again to  FIG. 2 , a conventional bonding process  200  is shown depicting a near final step of the of the current microfluidic device manufacturing process. An unbonded configuration  210  is shown at the top of  FIG. 2 . The unbonded configuration  210  undergoes a bonding process  200  and results in a bonded configuration  220  for the microfluidic chip. The bonding process can involve one or more of solvents, adhesives, elevated temperatures, and applied pressure. As described above, the bonding process  200  for current microfluidic fabrication techniques can be a common source of error and contributes to an overall low yield for current microfluidic manufacturing processes. The present invention addresses this poor yield by removing the bonding process  200 . 
     Referring to  FIG. 3A , a flowchart  300  illustrates an exemplary method for forming continuous channels (e.g., microfeatures and/or microchannels) in a transparent material. First, a laser source generates a laser beam  310 . An exemplary laser source can be a Lumentum PicoBlade from Lumentum of San Jose, Calif., U.S.A., which generates a laser beam having a pulse duration of nominally 10 picoseconds (ps) and a repetition rate in a range between a single pulse up to 8 megaHertz (MHz). In some embodiments, the laser beam has a wavelength that is within a range between about 400 nm and 4000 nm. Next, the laser beam is converged  320  using a focus optic. An exemplary focus optic is a Thorlabs AL1512-C objective lens (NA=0.546, 15.00 mm diameter). In some embodiments, the laser beam is converged  320  at a relatively high rate (e.g., at a numerical aperture [NA] greater than 0.3). Typically, the laser beam is converged  320  to a focal region that is first located outside of a transparent material. An exemplary transparent material is polymethyl methacrylate, PMMA (i.e., acrylic). Then, the laser beam is moved  330  relative the transparent material generally along a scan path that brings the focal region within the transparent material. The tracing of the focal region along the scan path forms a continuous channel  340 . As, the focal region is moved  330  from outside the transparent material to inside the transparent material ablation forms a vent port at an outer surface of the transparent material. According to some embodiments, the scan path is generally orthogonal to a surface of the transparent material as the focal region is moved from outside to inside the transparent material. Generally, the vent port allows for ablation product that is generated during the formation of the channel  340  to be removed to outside of the transparent material. The ablation product may initially contain a vapor which can create high pressures in an enclosed space. The pressure inside unvented channels may reach values high enough to create microcracks to form in the material. The product may also contain solid particulate or debris, which may block the channel. Finally, according to some embodiments, additional ablation product is removed from the channel  340 . In some cases, the ablation product is removed by way of a solution (e.g., water) and/or an ultrasonic cleaner. In some cases, resulting ablation product within the channels is one or more of an acid or base and the solution is a pH compliment of the ablation product. For example, product in channels formed within PMMA typically contain low molecular weight organic saturated acids (e.g., formic or acetic acid) and a solution with a basic pH can be used to clean out ablation product within the channel (e.g., sodium hydroxide or sodium hypochlorite) through chemical as well as mechanical means. According to some embodiments, before removing the ablation product from the channels  240  the laser beam is again moved (e.g., scanned) relative the transparent blank along one or more additional scan paths. Generally, these additional scan paths comprise contours parallel to the original scan path and are spaced apart from one another by a predetermined distance (e.g., about 1-100 μm). Moving the focal regions along the additional scan paths can cause a modification to the continuous channel (for example, increases a width/depth of the continuous channel or modifies a surface finish of the continuous channel). 
     Referring to  FIG. 3B , a top-down schematic view of a transparent material blank  360  is shown. The blank  360  has two fluidic ports  362 A-B. As described in greater detail below, the fluidic ports  362 A-B in some embodiments are preformed into the blank  360 . Meaning, the fluidic ports  362 A-B are formed before the continuous channels within the transparent material blank  360 . Three scan paths are shown between the two fluidic ports, a first scan path  364 , a second scan path  366 , and a third scan path  368 . All three of the scan paths  364 ,  366 , and  368  follow substantially parallel paths, which are separated by a separation distance  370 . A focal region  372 A-C is shown at the starting position for each scan path  364 ,  366 , and  368 . It can be seen that the focal region width in  FIG. 3B  is slightly larger than the separation distance  370 . Therefore, it is expected that a channel formed using the scan paths shown in  FIG. 3B  would result in one single continuous channel. Alternatively, in some embodiments, the separation distance  370  is equal to or larger than the focal region width and multiple scan paths typically result in multiple continuous channels being formed. Additionally, according to some embodiments a direction followed along the scan path is modified in order to further improve ablation product removal. 
     Referring now to  FIGS. 3C-E , three different scan direction arrangements are shown.  FIG. 3C  displays a unidirectional scan arrangement  380  that has all of the scans going in the same direction. The unidirectional scan arrangement  380  begins with a first scan path ‘A’ that starts at a top of the figure and goes to a bottom of the figure. A sequence of scans continue with scan ‘B’ and finally scan ‘C.’ As all of the scans are going to same direction,  FIG. 3C  is said to represent a unidirectional scan arrangement  380 . Bidirectional scan arrangements, where scan paths are followed in both directions, are also employed in some embodiments. 
       FIG. 3D  illustrates a first bidirectional scan arrangement  384 . The first bidirectional scan arrangement  384  begins with a first scan path ‘A’ that starts at a top of the figure and goes to a bottom of the figure. A sequence of scans continue with scan ‘B’ and finally scan ‘C.’ As the scans go in different directions (scan ‘B’ begins at the bottom of the figure and goes to the top of the figure),  FIG. 3D  is said to represent a type of a bidirectional scan arrangement. In some embodiments, longer continuous internal channels are able to be formed by using a bidirectional scan arrangement with vents located at each end of the channel. 
       FIG. 3E  illustrates a second bidirectional scan arrangement  390 . The second bidirectional scan arrangement  390  begins with a first scan path ‘A’ that starts at a top of the figure and goes to a bottom of the figure. A sequence of scans continue with scan  13 ′, scan ‘C’, scan ‘D’, and finally scan ‘E.’ As the scans go in different directions (scan ‘B’ and scan ‘D’ begin at the bottom of the figure and go to the top of the figure),  FIG. 3E  is said to represent a type of a bidirectional scan arrangement. Unlike the unidirectional scan arrangement  380  and the first bidirectional scan arrangement  384 , the second bidirectional scan arrangement  390  has the first scan (scan ‘A’) start in the middle and the following scans continue on each side of the first scan (scan ‘A’). In some embodiments, this type of scan arrangement is advantageous as it is often the first scan in a channel formation that causes the most ablation product and is most likely to cause microcracking. When this first scan path is located at an end of a resulting channel ablation product and microcracking are more pronounced then when it is located in a middle of the channel. 
     Referring now to  FIG. 4 , a system  400  for forming continuous channels in a transparent material is disclosed. The system  400  includes a laser source  410  (e.g., an ultrashort pulse laser having a pulse duration less than 100 nanoseconds). An exemplary laser source is a PicoBlade from Lumentum of San Jose, Calif., U.S.A. The laser source generates a laser beam  420  that is directed at a focus optic  430 . An exemplary focus optic is a 12 mm E.F.L. aspheric lens, for example Thorlabs Part No. AL512-C (which has an outer diameter of 15 mm and a numerical aperture (NA) of 0.546). The focus optic  430  converges the laser beam and directs it to a focal region  440 . In some embodiments, the focal region is first located external to a transparent material  450 . One or more translation stages  460  can move the transparent material and/or the focal region relative one another. Exemplary translation stages include direct drive linear servo motor stages and piezoelectric stages. In some cases, a controller  470  can control the laser source and/or the one or more translation stages. The controller  470  in some cases controls both laser source parameters (e.g., repetition rate and pulse duration) as well as translation stage parameters (e.g., scan path, scan speed, focal region location, number of scan paths, scan path separation distance). 
       FIG. 5A  illustrates a transparent material blank  500 , according to some embodiments, in two views. A first view  510  shows the blank at an angle. And, a second view  520  shows the blank at a cross-section. The blank  500 , as shown in  FIG. 5A , is unprocessed and contains no internal channels. The blank  500  however, does include 2 fluidic ports  540 . According to some embodiments, the fluidic ports are preformed before laser processing (e.g., machined or molded into the blank  500 ). Alternatively, the fluidic ports  500  may be formed with a laser at the time of internal channel generation. 
       FIG. 5B  shows a cross-sectional view  520  of the transparent material blank  500  as it undergoes laser processing to form a continuous channel. As shown in  FIG. 5B , a laser beam  552  is directed incident a focus optic  554 . The focus optic  554  converges the laser beam  552  to a focal region  556  and directs the laser beam into the transparent material. One or more translation stages move the transparent blank  500  in  3  axes (e.g., X, Y, and Z) relative the focal region  556  of the laser beam. The process as shown in  FIG. 5B , begins with the focal region  556  within a first fluidic port  540 A. The translation stages (not shown) then moves the blank  500  relative the focal region  556 , thereby producing the continuous channel  550 . Because of the starting position, the continuous channel  550  has a vent  558  to outside the material. The vent  558  allows ablation product to escape during channel formation. In some cases, without the vent  558  ablation product cools and reforms within the channel, preventing the formation of a continuous channel. In some embodiments, the continuous channel is configured to coincide with a second fluidic port  540 B (for example at the end of the continuous channel). Additional fluidic ports in excess of two may be used in some versions. According to some embodiments, the vent  558  is configured to be in fluidic communication with atmosphere. Alternatively, one or more vents may be configured to be in fluidic communication with a vacuum during processing. 
     Referring now to  FIGS. 6A-B , continuous channel formation systems and processes are described that include application of a vacuum.  FIG. 6A  illustrates a transparent material blank  600  undergoing laser processing to form a continuous channel  610 . The blank  600  includes two fluidic ports  620 A-B and a vacuum port  630 . The vacuum port is in fluidic communication with a vacuum system  632 . The vacuum system  632  includes a vacuum source (e.g., vacuum pump) that produces a vacuum (e.g., less than 760torr down to 0 ton). A laser beam  640  is directed incident a focus optic  642 , which converges the laser beam to a focal region  644 . Like the process described in reference to  FIG. 5B , the focal region  644  initially starts at a first fluidic port  620 A, and one or more translation stages (not shown) move the focal region  644  relative the blank  600  generally along a scan path to form the continuous channel  610 . As a result, a vent  646  is formed between the first fluidic port  620 A and the continuous channel  610 . The vent  646  allows ablation product that is formed during channel formation to escape the channel. The vacuum system  632  is in fluidic communication with the vent  646 , by way of the vacuum port  630  and the first fluidic port  620 A. The vacuum system therefore introduces a vacuum to the vent  646  and further increases a pressure gradient between an ablation pressure (locally formed within the channel during ablation) and a much lower vent pressure (e.g., less than atmosphere). 
       FIG. 6B  illustrates another embodiment, in which the entire blank  600  is placed within a vacuum chamber  650 , which is in fluidic communication with the vacuum system  632 . In the embodiment shown in  FIG. 6B , a surface  652  of the vacuum chamber is interposed between the focus optic  642  and the blank  600 . In this case, the surface comprises a material that is vacuum compatible and transparent at a wavelength of the laser beam. Exemplary materials include optical materials, such as: glass, quartz, sapphire, and industrial diamond. Some implementations can provide a new capability for forming internal channels in three-dimensions ( 3 D), for example microfluidic devices. 
       FIGS. 6C-D  schematically represents formation of a  3 D channel in a transparent blank  660 . A laser beam  662  is focused by a focus optic (not shown) and converged to a focal region  664 . The focal region  664  is shown within microfluidic features  666 . The microfluidic features  666  can be seen to be three dimensional ( 3 D) (see  FIG. 6D ). The microfluidic features  666  show in  FIGS. 6C-D  can be designed to separate different components within a fluid (e.g., cells within blood). The microfluidic features  666  provide fluidic communication between three fluidic ports  668 A-C. In order to produce functional microfluidic features  666 , it is possible to adjust process parameters to achieve desired microfluidic feature characteristics. 
     Parameter Selection 
     A number of parameters can be adjusted to control various characteristics of the channels. Considerations related to parameter selection are enumerated below. 
     Pulse duration of a pulsed laser beam has an important effect on the channel quality. Generally, shorter pulse durations result in less bulk heating of the non-ablated transparent material and fewer thermal effects result. For example, pulse durations of about 100 nanoseconds (ns) have been found to produce carbonization in internal channels formed within PMMA, according to some embodiments. 
     Pulse repetition rate of a pulsed laser beam along with scan speed can affect a pitch between adjacent laser pulses along a scan path. Therefore, pulse repetition rate can affect surface finish of a resulting channel. Pulse repetition rate is also controlled in some embodiments to manage overall (e.g., average) radiative power delivered to the transparent material. Although, the transparent material is largely non-absorbing to the laser beam, some small amount (e.g., less than 1%) of the delivered energy can be absorbed optically. Additionally, in some cases much of the energy (e.g., greater than 10%) of the delivered energy is retained within the transparent material after ablation product cools. Therefore, it can be desirable in some embodiments to control the overall amount of radiative power delivered to the transparent material. 
     Wavelength can be selected in part based upon laser sources, which are commercially available. Ultrashort pulse duration lasers are currently limited to a number of wavelengths. Additionally, in some embodiments, wavelength is selected in order to achieve a desired absorption (e.g., linear, multi-photon, non-linear, etc.) of the transparent material. 
     Numerical aperture (NA) and focal region width are optical parameters that are related. The focal region width in some embodiments, is selected based upon a desired minimum feature size (e.g., desired minimum channel width). Alternatively, in some embodiments, focal region width is selected in order to achieve a desired minimum fluence/irradiance value, to produce desired ablation characteristics. 
     Scan path separation distance, or a distance between adjacent scans that together comprise a single channel, can affect surface finish of a resulting channel. For example, in general, a larger separation distance between adjacent scan paths can result in a rougher surface finish within the resulting continuous channel. Also, in some embodiments, separation distance between adjacent scan paths can be selected to control resulting channel height. For example, a smaller separation distance between adjacent scan paths can result in greater accumulated energy with the channel and causes an elongation of the height of the channel. 
     A number of scans per channel parameter can be related to the separation distance between adjacent scan paths. In many embodiments, the number of scans per channel parameter is controlled in order to produce a desired channel width, given a set separation distance between adjacent scans. 
     Scan speed is another parameter that can affect surface roughness and height of the resulting channel. For example, slower scan speeds (all else being equal) can result in smoother and higher channel formation. Additionally, scan speed affects accumulation of radiative energy within local areas in the transparent material. For example, faster moving scan speeds (all else being equal) can allow less total energy to be directed to any given location of the transparent material proximal the scan path. 
     A length of channel parameter is a total path length of the channel to nearest vent. This parameter is controlled to be kept below a desired threshold in order to ensure that ablation product is able to escape through the vent and the channels are kept continuous. For example, a length of channel that is too long prevents the ablation product from escaping the channel and the ablation product forms a blockage within the channel preventing fluidic flow within the channel. 
     Considerations related to parameter selection are described above. In order to further aid in parameter selection a table containing exemplary parameter ranges is disclosed below: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 Parameter 
                 Min. 
                 Nom. 
                 Max. 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Pulse  
                 1  
                 fs 
                 100  
                 fs 
                 1000  
                 ns 
               
               
                 duration 
                   
                   
                   
                   
                   
                   
               
               
                 Pulse  
                 1  
                 Hz 
                 4  
                 kHz 
                 100  
                 kHz 
               
               
                 repetition  
                   
                   
                   
                   
                   
                   
               
               
                 rate 
                   
                   
                   
                   
                   
                   
               
               
                 Wavelength 
                 400  
                 nm 
                 1064  
                 nm 
                 4000  
                 nm 
               
            
           
           
               
               
               
               
            
               
                 Numerical  
                 0.01 
                 0.5 
                 1.0 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 aperture 
                   
                   
                   
                   
                   
                   
               
               
                 (NA) 
                   
                   
                   
                   
                   
                   
               
               
                 Focal region  
                 0.01  
                 μm 
                 2  
                 μm 
                 500  
                 μm 
               
               
                 width 
                   
                   
                   
                   
                   
                   
               
               
                 Scan path 
                 0.01  
                 μm 
                 2  
                 μm 
                 500  
                 μm 
               
               
                 separation  
                   
                   
                   
                   
                   
                   
               
               
                 distance 
                   
                   
                   
                   
                   
                   
               
               
                 Scan speed 
                 0.01  
                 mm/s 
                 2  
                 mm/s 
                 5000  
                 mm/s 
               
            
           
           
               
               
               
               
            
               
                 No. of scans  
                 1 
                 10 
                 10,000,000 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 per channel 
                   
                   
                   
                   
                   
                   
               
               
                 Length of  
                 0.1  
                 mm 
                 50  
                 mm 
                 10  
                 m 
               
               
                 channel 
                   
                   
                   
                   
                   
                   
               
               
                 Width of  
                 1  
                 μm 
                 100  
                 μm 
                 10000  
                 μm 
               
               
                 channel 
                   
                   
                   
                   
                   
                   
               
               
                 Depth of  
                 10  
                 μm 
                 15  
                 μm 
                 350  
                 μm 
               
               
                 channel 
                   
                   
                   
                   
                   
                   
               
               
                 Vacuum  
                 0  
                 torr 
                 1  
                 torr 
                 760  
                 torr 
               
            
           
           
               
               
               
               
            
               
                 Pressure 
                   
                   
                   
               
            
           
           
               
               
            
               
                 Transparent 
                 General Purpose Polystyrene (GPPS), Methylmethacrylate 
               
               
                 material 
                 Acrylonitrile Butadiene Styrene (MABS), Styrene  
               
               
                   
                 acrylonitrile (SAN), Styrene Methyl Methacrylate (SMMA),  
               
               
                   
                 Methacrylate Butadiene Styrene (MBS), Styrene-butadiene  
               
               
                   
                 (SB) Copolymer, Polycarbonate (PC), High Heat  
               
               
                   
                 Polycarbonate (HH PC), Polyethylene Terephthalate (PET),  
               
               
                   
                 Glycol-Modified Polyethylene Terephthalate (PET-G),  
               
               
                   
                 Poly(Methyl Methacrylate) (PMMA), Polyethyleneimine  
               
               
                   
                 (PEI), Polyethersulfone (PES), Polysulfone (PSU),  
               
               
                   
                 Polypropylene Homopolymer (PP H), Random  
               
               
                   
                 Copolymerized Polypropylene (PP R), Low-Density  
               
               
                   
                 Polyethylene (LDPE), Polylactic Acid (PLA), glass,  
               
               
                   
                 Styrene-Ethylene/Butylene-Styrene (SEBS), Thermoplastic  
               
               
                   
                 Polyurethane (TPU), and Thermoplastic Olefin (TPO),  
               
               
                   
                 crystal, sapphire, and quartz 
               
               
                   
               
            
           
         
       
     
     Example Embodiments 
     A number of trials were performed to demonstrate channel formation within a transparent material. The details of these trials are described in detail below.  FIG. 7  is an image showing an embodiment of a system used to form continuous channels within a transparent material. A sample holder  710  can provide a secure mount for a transparent material blank  712 . An inspection camera  714  was directed downward and used to aid in alignment of the blank  712 . A laser source  716  was used to generate a laser beam. The laser source used was a Lumentum PicoBlade operating with a 1064 nm wavelength and a pulse duration of 10 pS nominal. The laser beam was directed through a focus optic  718 . The focus optic used was a 12 mm E.F.L. aspheric lens (Thorlabs Part No. AL1512-C). The aspheric lens had a numerical aperture (NA) of 0.546 and an outside diameter of 15 mm nominal. A stage assembly  720  was used to move the sample holder  710  relative the focus optic  718  and thereby produce a relative motion between a focal region of the laser beam and the transparent blank  712 . 
     A number of transparent material blanks  712  were produced out of clear PMMA. The blanks all had one or more preformed fluidic ports. The channels were formed by first starting each scan path within a fluidic port and ending the scan path within another fluidic port. After channel formation, testing was performed to show that the formed channels were continuous and substantially free from blockage.  FIG. 8  illustrates an exemplary channel test  800  to test for blockage within the channel. A blank  810  is shown having an internal continuous channel  812  between a first fluidic port (not shown) and a second fluidic port  814 . A syringe  816  containing air is sealed in fluidic communication with the first fluidic port and dye containing deionized (DI) water is placed within the second fluidic port  814 . As, the syringe  816  is compressed, bubbles  820  form within the dye containing DI water within the second fluidic port  814 , indicating fluidic communication throughout the channel  812 . 
     In order to demonstrate channel surface characteristics (e.g., surface roughness and channel height), a number of surface channels were formed on a surface (not inside) of a clear PMMA blank. In order to form the surface channels, the focal region was placed coincident with a top surface of the blank. The following process parameters were used in forming all of the surface channels: 1064 nm wavelength, 10 ps, 4 kHz pulse repetition rate, and 2 mm/s scanning rate. A separation distance parameter was varied.  FIGS. 9A-D  are scanning electron microscope (SEM) images of surface channels with differing separation distances between adjacent scan paths.  FIG. 9A  illustrates a surface channel forming with a separation distance parameter of 2 micrometers.  FIG. 9B  illustrates a surface channel forming with a separation distance parameter of 5 micrometers.  FIG. 9C  illustrates a surface channel forming with a separation distance parameter of 7 micrometers.  FIG. 9D  illustrates a surface channel forming with a separation distance parameter of 10 micrometers. It can be seen from  FIGS. 9A-D  that as spacing between adjacent scan paths increases, height and roughness of the resulting channel also increase. 
     Referring to  FIG. 10 , in order to demonstrate channels with different lengths (e.g., scan path lengths), a number of internal channels were formed inside of a clear PMMA blank  1010 . The blank  1010  had  12  (6 pairs) preformed fluidic ports  1012 . A distance between pairs of the fluidic ports varied from 5 mm to 10 mm in increments of 1 mm, with channel  1   1021  being 5 mm long; channel  2   1022  being 6 mm long; channel  3   1023  being 7 mm long; channel  4   1024  being  8 mm long; channel  5   1025  being 9 mm long; and, channel  6   1026  being 10 mm long. All, 6 channels were formed using identical process parameters including: 40 total bidirectional scans with a lateral separation distance of 10 micrometers (channel width of 200 micrometers nominal) and a vertical separation distance of 50 micrometers (first focal region depth at 500 micrometers and second focal region depth at 450 micrometers). The following process parameters were used in forming all of the internal channels: 1064 nm wavelength, 10 ps, 4 kHz pulse repetition rate, and 2 mm/sec scanning rate. Finally, the blank  1010  was placed in an ultrasonic bath for 300 seconds. All channels  1021 - 1026  were tested by the method described above and found to be continuous and free from blockage. 
     Referring now to  FIG. 11 , to demonstrate multiple channels at different depths, a number of internal channels were formed inside of a clear PMMA blank  1110 . The blank had 10 (5 pairs of) preformed fluidic ports  1112 . A distance between pairs of fluidic ports was 5 mm for all fluidic port pairs. Laser parameters included: 1064 nm wavelength, 10 ps, 4 kHz pulse repetition rate, and 2 mm/sec scanning rate. Parameters for the 5 pairs of fluidic ports are included in the table below: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                   
                   
                 Scan Path 
                   
                   
                 Total  
               
               
                   
                   
                 Separation 
                 Channel 
                 Focal  
                 Number 
               
               
                 Channel  
                 FIG. 
                 Distance 
                 Width 
                 Region 
                 of Scan 
               
               
                 ID 
                 Numeral 
                 (μm) 
                 (μm) 
                 Depth 
                 Passes 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 1121 
                 5 
                 200 
                 500, 450 
                 80 
               
               
                 2 
                 1122 
                 10 
                 400 
                 500, 450 
                 80 
               
               
                 3 
                 1123 
                 20 
                 800 
                 500, 450 
                 80 
               
               
                 4 
                 1124 
                 5 
                 100 
                 500, 450, 
                 80 
               
               
                   
                   
                   
                   
                 1000, 950 
                   
               
               
                 5 
                 1125 
                 10 
                 100 
                 500, 450, 
                 40 
               
               
                   
                   
                   
                   
                 1000, 950 
                   
               
               
                   
               
            
           
         
       
     
     It can be seen in  FIG. 11 , that channel  4   1124  and channel  5   1125  include two channels at two different depths, demonstrating an ability of some embodiments of the invention to produce channels in three dimensions. All of the channels  1121 - 1125  (channels  1 - 5 ) were tested before ultrasonic cleaning and found to be obstructed. After the blank  1110  was placed in an ultrasonic bath for 300 seconds, all of the channels  1121 - 1125  (channel  1 - 5 ) were retested and found to continuous and free from blockage. Said another way, all of the channels were cleared of ablation product during ultrasonic cleaning. 
     Referring now to  FIG. 12 , to demonstrate generation of functional microfluidic devices, a number of channels were formed inside of a clear PMMA blank  1210 . The blank  1210  had four sets of three or four preformed fluidic ports  1212 . Between the four sets of preformed holes, four structures were formed capable of simple cell sorting. A first structure  1221  and a second structure  1222  both had a spacing between fluidic ports  1212  of 10 mm nominally. A third structure  1223  and a fourth structure  1224  both had a spacing between fluidics ports  1212  of 5 mm nominally. Laser parameters included: 1064 nm wavelength, 10 ps, 4 kHz pulse repetition rate, and 2 mm/sec scanning rate. Parameters for the 5 pairs of fluidic ports are included in the table below: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                   
                   
                 Scan Path 
                   
                   
                 Total  
               
               
                   
                   
                 Separation 
                 Channel 
                 Focal  
                 Number 
               
               
                 Structure  
                 FIG  
                 Distance  
                 Width  
                 Region 
                 of Scan 
               
               
                 ID 
                 Numeral 
                 (μm) 
                 (μm) 
                 Depth 
                 Passes 
               
               
                   
               
             
            
               
                 1 
                 1221 
                 10 
                 100 
                 500, 475, 450 
                 30 
               
               
                 2 
                 1222 
                 10 
                 100 
                 500, 475, 450 
                 30 
               
               
                 3 
                 1223 
                 10 
                 100 
                 500, 475, 450 
                 30 
               
               
                 4 
                 1224 
                 10 
                 100 
                 500, 475, 450 
                 30 
               
               
                   
               
            
           
         
       
     
     It can be seen in  FIG. 12 , that all of the structures (structure  1 - 4 ) are formed inside the blank  1210 . All of the structures  1221 - 1224  were tested before ultrasonic cleaning and found to be continuous and free from ablation product. Even though the structures were unobstructed, the blank  1210  was placed in an ultrasonic bath for 300 seconds. All of the structures (structure  1 - 5 ) were retested and found again to be continuous and free from blockage. 
     Although a few variations have been described in detail above, other modifications or additions are possible. For example, the variations described above largely describe embodiments in which the transparent material is moved as the focal region remains stationary. Additionally, the focal region in some embodiments is moved (for example, with beam scanners, moving optics, etc.) and the transparent material is held stationary. 
     In the descriptions above and in the claims, phrases such as “at least one of” or “one or more of” may occur followed by a conjunctive list of elements or features. The term “and/or” may also occur in a list of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which it is used, such a phrase is intended to mean any of the listed elements or features individually or any of the recited elements or features in combination with any of the other recited elements or features. For example, the phrases “at least one of A and B;” “one or more of A and B;” and “A and/or B” are each intended to mean “A alone, B alone, or A and B together.” A similar interpretation is also intended for lists including three or more items. For example, the phrases “at least one of A, B, and C;” “one or more of A, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together.” In addition, use of the term “based on,” above and in the claims is intended to mean, “based at least in part on,” such that an unrecited feature or element is also permissible. 
     Values or ranges may be expressed herein as “about” and/or from/of “about” one particular value to another particular value. When such values or ranges are expressed, other embodiments disclosed include the specific value recited and/or from/of the one particular value to another particular value. Similarly, when values are expressed as approximations, by the use of antecedent “about,” it will be understood that here are a number of values disclosed therein, and that the particular value forms another embodiment. It will be further understood that there are a number of values disclosed therein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. In embodiments, “about” can be used to mean, for example, within 10% of the recited value, within 5% of the recited value or within 2% of the recited value. 
     For purposes of describing and defining the present teachings, it is noted that unless indicated otherwise, the term “substantially” is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term “substantially” is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety. Any patent, publication, or information, in whole or in part, that is said to be incorporated by reference herein is incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in this document. As such, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. 
     The subject matter described herein can be embodied in systems, apparatus, methods, and/or articles depending on the desired configuration. The implementations set forth in the foregoing description do not represent all implementations consistent with the subject matter described herein. Instead, they are merely some examples consistent with aspects related to the described subject matter. Although a few variations have been described in detail above, other modifications or additions are possible. In particular, further features and/or variations can be provided in addition to those set forth herein. For example, the implementations described above can be directed to various combinations and sub-combinations of the disclosed features and/or combinations and sub-combinations of several further features disclosed above. In addition, the logic flows depicted in the accompanying figures and/or described herein do not necessarily require the particular order shown, or sequential order, to achieve desirable results. Other implementations may be within the scope of the following claims.