Abstract:
Aerosol and hydrosol particle detection systems without knowledge of a location and velocity of a particle passing through a volume of space, are less efficient than if knowledge of the particle location is known. An embodiment of a particle position detection system capable of determining an exact location of a particle in a fluid stream is discussed. The detection system may employ a patterned illuminating beam, such that once a particle passes through the patterned illuminating beam, a light scattering is produced. The light scattering defines a temporal profile that contains measurement information indicative of an exact particle location. However, knowledge of the exact particle location has several advantages. These advantages include correction of systematic particle measurement errors due to variability of the particle position within the sample volume, targeting of particles based on position, capture of particles based on position, reduced system energy consumption and reduced system complexity.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/802,088, filed on May 18, 2006. The entire teachings of the above application are incorporated herein by reference. 
    
    
     GOVERNMENT SUPPORT 
     The invention was supported, in whole or in part, by a grant F 19628-00-C-0002 from DARPA, MTO. The Government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     The ability to detect and classify small particles in a fluid stream has been of great use in many fields. For example, the detection of harmful particles or biological agent particles in air (outdoors or inside a building) or in water (a city water supply) may require monitoring the air or water for such particles. 
     SUMMARY OF THE INVENTION 
     Aerosol and hydrosol particle detection systems typically do not determine the exact location of an individual particle as it passes through the detection system sample volume. However, knowledge of the exact particle location has several advantages. These advantages include correction of systematic particle measurement errors due to variability of the particle position within the sample volume, targeting of particles based on position, capture of particles based on position, reduced system energy consumption and reduced system complexity. 
     An apparatus and method for use for detecting a location of a particle in a fluid stream is described herein. In one example embodiment, the apparatus for measuring a position of a particle in a flow comprises a light source that may be used to generate an illuminating beam to travel in a first dimension and define an illumination pattern in second and third dimensions. The apparatus may further comprise a light detector to detect a temporal profile of scattered light (including elastic scattering, luminescence, and/or Raman scattering) produced by the particle&#39;s passing through the illumination pattern in the second dimension. The apparatus may also include a processing unit, coupled to the light detector, to determine the position of the particle, in the third dimension relative to the illumination pattern, based on the temporal profile of the scattered light and a geometrical relationship of the illumination pattern. 
     The apparatus may further include a masking element in optical arrangement with the light source. The masking element may cause the illuminating beam to define a plurality of regions of the illumination pattern, where at least two regions may comprise varying intensities or polarizations. A specific example of the illuminating beam defining at least two regions of varying intensities of the illumination pattern is where at least one of the regions of the illumination pattern has a measurably different intensity than any of the other regions (i.e., a zero or substantially zero beam intensity). 
     In at least one example embodiment, the light source may be a first light source, the illuminating beam may be a first illuminating beam, the illuminating pattern may be a first illuminating pattern, the temporal profile may be a first temporal profile, and the scattered light may be a first scattered light. Thus, the apparatus may also include a second light source, which may generate a second illuminating beam to travel in a third dimension, the illuminating beam may define a second illumination pattern in first and second dimensions. The detector may further detect a second temporal profile caused by a second scattered light produced by the particle&#39;s passing through the second illuminating pattern. The processing unit may be configured to determine the position of the particle, in the first dimension relative to the second illumination pattern, which may be based on the second temporal profile of the second scattered light and a geometrical relationship of the second illumination pattern. 
     In another example embodiment, the apparatus may further comprise a modulator to modulate the intensity of the illuminating beam and the intensity of a second illuminating beam. The detector may be a first detector, and the apparatus may further comprise a second detector configured to detect the second temporal profile. The apparatus may also comprise a coding element configured to code distinctly the illumination pattern and the second illumination pattern. 
     In some example embodiments, the first and second light sources of the apparatus may be configured to illuminate the first illuminating beam and the second illuminating beam at different wavelengths. The apparatus may also comprise a polarizer, in optical arrangement with the light source to distinctly polarize the first illuminating beam and the second illuminating beam. 
     In another embodiment, the apparatus may further include a patterned optical block. The patterned optical block may comprise a plurality of blocking regions that may be positioned to receive the scattered light. The apparatus may comprise a light shield to shield the illuminating beam, in a manner allowing the scattered light to be received by the optical block, and may further comprise a focusing element to focus the scattered light onto the optical block. The detector may detect a combined temporal profile that may be produced by the particle&#39;s passing through the illumination pattern and the plurality of blocking regions on the optical block. The processing unit may determine the position of the particle, in the first dimension relative to the illumination pattern, that may be based on the combined temporal profile of the light scattering. 
     The processing unit may be configured to measure a relative amount of light of the combined temporal profile that may be blocked from the plurality of blocking regions with respect to an amount of light unblocked by the plurality of blocking regions. The apparatus may also comprise a calculation unit to determine a normalization or correction value, which may be based on a measurement from a standard particle at a known position, to apply to subsequent measurements of nonstandard particles at this same known position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
         FIGS. 1A and 1B  are diagrams with examples of particle detection systems; 
         FIG. 2  is a schematic diagram of a patterned beam particle detection system for determining a position of a particle in one dimension, according to an embodiment of the present invention; 
         FIG. 3  is a flow diagram of an overview of operative steps of the detection system of  FIG. 2 ; 
         FIG. 4  is a perspective view of an example patterned beam, defining an illumination pattern, illuminating particles in a sample volume of a flow, according to an embodiment of the present invention; 
         FIG. 5  is a depiction of an example illumination pattern and measured signal produced by detecting particles by the systems illustrated in  FIGS. 1A and 1B ; 
         FIGS. 6A and 6B  are diagrams of example geometrical configurations of the illumination pattern; 
         FIG. 7  is a schematic diagram of a patterned beam particle detection system for determining a position of a particle in two physical dimensions in an air flow, according to an embodiment of the present invention; 
         FIG. 8  is a flow diagram of an overview of operations of the detection system of  FIG. 7 ; 
         FIG. 9  is a depiction of an example of a polarization masking element, according to an embodiment of the present invention; 
         FIG. 10  is a schematic diagram of a patterned beam particle detection system featuring polarization coding for determining a position of a particle in two physical dimensions in an air flow, according to an embodiment of the present invention; 
         FIG. 11  is a schematic diagram of a patterned beam particle detection system featuring modulation coding for determining a position of a particle in two physical dimensions in an air flow, according to an embodiment of the present invention; 
         FIGS. 12A and 12B  are schematic diagrams of a patterned beam particle detection system featuring illumination wavelength coding to determine a position of a particle in two physical dimensions in an air flow, according to an embodiment of the present invention; 
         FIGS. 13A and 13B  are schematic diagrams of an optical block particle detection system for determining a position of a particle in an air flow, and an example measurement signal, respectively, according to an embodiment of the present invention; 
         FIG. 14  is a flow diagram of an overview of operations of the detection system of  FIGS. 13A and 13B ; 
         FIGS. 15A and 15B  are a schematic diagram of an optical block particle detection system for determining a position of a particle in an air flow and example measurement signals, respectively, according to an embodiment of the present invention; 
         FIG. 16  is a schematic diagram of an optical block and patterned beam particle detection system for determining two positions of a particle in an air flow, according to an embodiment of the present invention; 
         FIG. 17  is a flow diagram of an overview of operations of the detection system of  FIG. 16 ; 
         FIG. 18  is a depiction of a measured signal that may be obtained using the system of  FIG. 16 ; and 
         FIG. 19  is a depiction of a measurement normalization (or correction) using a patterned beam particle detection system, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of example embodiments of the invention follows. 
       FIG. 1A  provides an example  100  of a particle detection system  101 . The particle detection system  101  may be situated to detect particles  104  in an airvent system  105  of a building  103 . The particle detection system  101  includes an inlet (not shown) in which an airflow enters the particle detection system  101 . An outlet  106  of the particle detection system  101  may be used as a pathway to shunt the airflow if particles  102  detected are deemed unsafe for breathing. Otherwise, the airflow can continue into the airvent system  105 . 
     As another example, a liquid stream may also need to be evaluated. For instance, a water reservoir may need to be continuously monitored to ensure harmful particles are not introduced into a water supply.  FIG. 1B  provides an example  107  of a particle detection system  111  detecting particles  113  in a liquid stream  109 . The particle detection system  111  may include an inlet  115  used to supply a sample of the liquid flow  109  to the particle detection system  111 . Once the liquid flow  109  has been checked for a presence of foreign particles, an outlet  117  may be used to remove the sample from the particle detection system  111 . 
       FIG. 2  provides an example of a particle detection system  200  according to an embodiment of the present invention.  FIG. 3  shows a flow diagram  300  of an overview of operations that may be taken by the detection system  200 . Referring to  FIG. 2  with references to  FIG. 3 , the particle detection system  200  may include a light source  201  configured to emit a propagating beam  203 , also referred to herein as an “illuminating light beam,” traveling in the z dimension, or a first dimension. A masking element  205  may be coupled to the light source  201  to produce a light beam pattern  207  also referred to herein as an “illuminating pattern,” in x and y dimensions, or second and third dimensions, respectively ( FIG. 3 ,  301 ). It should be appreciated that the light beam  207  shown in  FIG. 2  is rotated 90 degrees about its vertical axis as represented in the Figure. It should also be appreciated that instead of the light beam pattern shown ( 207 ) any other light beam pattern may be employed in the detection system  200 . 
     The propagating light beam  203  defines the beam pattern  207  at a sample volume  209  within a particle flow  210 . The sample volume  209  may be configured to “receive” the flow in the x axis, or the second dimension. As the particles (not shown) in the sample volume  209  pass through the propagating beam  203 , defining the beam pattern  207  ( FIG. 3 ,  303 ), a diverging light scattering  211  is produced as a result of a collision of photons with the particles passing through the beam pattern  207 . 
     The diverging light scattering  211  has a temporal profile that is a function of the beam pattern  207 . For example, for the beam pattern  207 , the temporal profile exhibits a first period of signal (i.e., scattering), short period of no or very low signal as the particle passes through the gap in the beam pattern, and then a second period of signal. Accordingly, the temporal profile has a timing indicative of the particle&#39;s position in the sample volume  209  in the y, or third, dimension. An optical focusing element  213  may be used to focus the produced diverging scattered light  211 , resulting in converging scattered light  217 . An optical beam blocker  215  may be used to block the propagating beam  203 , thereby preventing the propagating beam  203  from directly reaching the light detector  219  and, thus, preventing detector saturation. The converging scattering light  217  may be focused onto the light detector  219  for detection ( FIG. 3 , step  305 ). 
     In this example embodiment, the light detector  219  is coupled to a processing unit  221 . The light detector  219  may be configured send data measurements  223  to the processing unit  221  in the form of an analog electrical signal. The processing unit  221  may be configured to determine the position of the particle in the third dimension, relative to the illumination pattern  207 , based on the temporal profile of the detected scattered light  217  ( FIG. 3 , step  307 ). The processing unit  221  may send measurement instructions  225  to the light detector  219  in the case of intelligent, programmable configurable. The measurement instructions  225  may include, for example, on/off instructions. The light detector  219  and the processing unit  221  may be connected via a connection link  227 . It should be appreciated that the connection link  227  may be a wired, optical, or wireless connection, or any other data transfer connection known in the art. 
     The processing unit  221  may also be connected to a database storage  229 . The processing unit  221  may send the database storage  229  a particle identification request, and/or a data storage request  231 . The data storage request  231  may include the data measurements  223 , or representation thereof, provided by the light detector  219 . The particle identification request may include a request to compare information stored in the database storage  229  with the obtained data measurements  223 , optionally for the purpose of classifying and identifying the particles in the sample volume  209 . The database storage  229  may send a particle identification result  233  to the processing unit  221 . The particle identification result  233  may comprise a listing of possible particle matches with respect to the data measurements  223 . 
     The processing unit  221  may also be coupled to a network  237 . The processing unit  221  may send a particle identification request, a data storage request, and/or a data sharing request  239  to the network  237 . The particle identification request and data sharing request  239  may be similar to the request  231  sent to the database storage  229 . The data sharing request  239  may be a request to share data with a user  236  that may be connected to the network  237 , or another detection system  238  that may be connected to the network  237 . The network  237  or, more specifically, a server or other network element (not shown) connected to the network  237 , may also send a message  241  in the form of particle identification results, similar to the result  233  sent by the database storage  229 , or instructions to the processing unit  221 . The instructions  241  may be comprise measurement instructions similar to the instructions  225  sent to the light detector  219 . 
     The database storage  229  and the network  237  may also include a bidirectional data transfer connection  249 . The database storage  229  may send identification results and/or a data sharing request  247  to the network  237 . The network  237  may send an identification request  245  to the database storage  229 . It should be appreciated that the data transfer connections  235 ,  243 , and  249  between the processing unit and the data storage, the processing unit and the network, and the network and the data storage, respectively, may include or be supported by any data transmission link known in the art. It should also be appreciated that the configuration shown in  FIG. 2  of the particle detection system  200  is merely an example. Any other dimensional configuration may be employed, preferably with the first, second, and third dimensions orthogonal to one another. 
       FIG. 4  provides an expanded view  400  of the intersection of the particle air flow  402  and the propagating light beam  403 , resulting in a sample volume  409 . The propagating light beam  403  may be configured to travel in the z, or first, dimension. As is shown in  FIG. 4 , the propagating light beam  403  may comprise a light beam pattern  407 , similar to the pattern  207  shown in  FIG. 2 . The light beam pattern  407  may, for example, be defined by a square shaped beam with a center diagonal region having an intensity that is substantially equal to zero or substantially less than the intensity of the surrounding portion(s) of the light beam pattern. The particle air flow  402  may be transmitted in the x, or second, dimension. The sample volume  409  may include any number of particles  410  traveling in the particle air flow. However, it is expected that only one particle at a time will pass through the sample volume  409  at a time or, if more than one particle passes through at a time, they pass through at positions sufficiently distinguishable from each other. It should be appreciated that any geometrical configuration may be employed, provided that the first, second, and third dimensions are orthogonal to each other, in a preferred embodiment. 
       FIG. 5A  provides a detailed schematic diagram  500  of an example light beam pattern  502 . The light beam pattern  502  may be formed with different regions of varying intensity. For example, the pattern  502  may include a first region  501 , second region  503 , and third region  505 , with the second region  503  having an intensity that may be measurably less (e.g., 5%, 20%, 50%, 80%, or 100% less) than the intensity of the first and/or third regions  501 ,  505 , respectively. An angle θ 507  defines a sloping of the diagonal second region  503  in this example embodiment. A label ‘x 0 ’  509  represents the smallest distance a particle (not shown) may pass through the first region  501  before reaching the second region  503 . The light beam pattern  502  may be defined by a total distance (D)  511 . A position of the particle in the y, or a third, dimension  513  represents a transverse location of the particle in a particle path  515 . The transverse location y may be obtained using the geometrical properties of the beam pattern  502  and the temporal profile (described in reference to  FIG. 5B  below) produced by the particle&#39;s passing through the light beam pattern  502  and the geometric properties of the beam pattern. 
       FIG. 5B  represents an example of a measured light signal produced by a particle in the particle path  515  traveling through the beam pattern  502 . The measured light signal  515  may comprise three distinct portions. The first portion, labeled t 1 ,  521  represents the time the particle in the particle path  515  took to pass through the first region  501  of the light beam pattern  502 . As the particle in the particle path  515  passes through the first region  501  of the beam pattern  502 , the particle may produce a scattered light, of an intensity represented as a signal level in the region t 1    521  of the measured light signal  517 . As the particle in the particle path  515  passes through the second region  503  of the light pattern  502 , no scattered light, or a substantially small amount of scattered light, may be produced due to the low intensity of the second region  503 . Therefore, the region labeled as t 2    523  of the measured light signal  517  has a very low intensity reading as compared to that of t 1    521 . The region labeled as t 3    525  is a representation of the measured scattered light produced by the particle in the particle path  515  passing through the third region  505  of the light beam pattern  502 . As expected, the signal reading in the region t 3    525  is greater than that of t 2    523 , since the third region of the pattern  505  has a greater intensity than that of the second region  503 . 
     It should be understood that the intensities of the light beam pattern  502  may be inverted such that the first and third regions  501 ,  505  are dimmer (i.e., have less intensity) than the second region  503 . In this alternative light beam pattern  502  example, the measurements at t 1 , t 2 , and t 3  are based on the inverted levels of intensity. The relative timing is dependent only on the geometry of the intensity pattern  502 . The absolute timing additionally depends on the velocity of the particle through the pattern  502 . 
       FIG. 5C  is a graphical representation  527  of the measured light signal  517  from a real particle. The graphical representation  527  is a plot of the intensity signal measured in millivolts (mv)  529  versus the entire time the particle passed through the light beam pattern  502 , measured in milliseconds (ms)  531 . The time signals t 1    521  and t 3    525  include high intensity signal readings since the first and third regions  501  and  505 , respectively, of the light beam pattern  502  have light with a substantial greater intensity than that of the second region  503 , represented by the intensity reading t 2    523 . Therefore, the first and third regions  501  and  505  produce a greater amount of scattered light when the particle passes through. The measurement t 2    523  provides a very low intensity signal reading in this example due to the fact that the light intensity of the second region  503  is substantially less than the first and third regions  501  and  505 , respectively, therefore producing a lesser amount of scattered light when the particle passes through it. 
       FIGS. 6A and 6B  provide a depiction of the geometric relationship between the particle in the particle path and the patterned light beam  600   a . In  FIG. 6A  the patterned beam  600   a  may include different regions of varying intensity. For example, the patterned light beam  600   a  a first region  601 , second region  603 , and third region  605 , with the second region having an intensity that may be substantially less than the intensity of the first and/or third regions  601 ,  605 , respectively. The time taken for a particle to pass through the first  601 , second  603 , and third  605  regions is represented by t 1    615 , t 2    617 , and t 3    619 , respectively. An angle θ  607  defines a sloping of the diagonal second region  603  in this embodiment. The label ‘x 0 ’  609  represents the smallest distance a particle may pass through the first region  601  before reaching the second region  603 . The light beam pattern  600   a  may be defined by a total distance (D)  611 . A position of the particle in the y, or third, dimension  613 , representing a transverse location of the particle in a particle path  612  may be obtained using the geometrical properties of the pattern  600   a  and time signals by t 1    615 , t 2    617 , and t 3    619 . The label ‘x’  621  represents a side of a triangle, formed in the first region  601 , by the transverse position y  613  and the angle θ  607 . The term ‘vt 1 ’ represents a mathematical expression of the distance traveled in the first region  601  by the particle in the particle path  612 . 
     Using the geometrical configuration described above, it should be appreciated that the total time taken for a particle to pass through the pattern beam  600   a  may be represented by equation (1):
 
 T=t   1   +t   2   +t   3   (1)
 
The relationship between a total distance (D) and a total time (T) may be used to find a velocity (v) of the particle traveling in the particle path  612 , as shown in equation (2):
 
                   v   =     D   T             (   2   )               
Using the tangent relationship of the angle θ  607  with respect to the transverse position y  613  and x  621 , equation (3) may be derived:
 
                     y   x     =     tan   ⁡     (   θ   )               (   3   )               
Solving for x in equation (3) yields the following equation:
 
                   x   =     y     tan   ⁡     (   θ   )                 (   4   )               
Using the geometrical relationship between ‘vt 1 ’  623 , x 0    609 , and x  621  shown in  FIG. 6A , the following equation may be obtained:
   x   0   +x=vt   1   (5) 
Since the value of the distance (D)  611  of the pattern  600   a  may be substantially small, it may be assumed that the velocity of the particle traveling the first region  601  is equal to the velocity of the particle traveling through the entire pattern. Thus, the value for the particle velocity (v) obtained in equation (2) may be substituted into equation (5) yielding:
 
                       x   0     +   x     =       vt   1     =       Dt   1     T               (   6   )               
Substituting the value of x from equation (4) into equation (6) yields:
 
                       x   0     +     y     tan   ⁡     (   θ   )           =       vt   1     =       Dt   1     T               (   7   )               
Finally, solving for the transverse particle position value (y) in equation (7) yields:
 
                   y   =       (         Dt   1     T     -     x   0       )     ⁢     tan   ⁡     (   θ   )                 (   8   )               
Thus, based on the measurements t 1    615 , t 2    617 , and t 3    619 , as well as knowledge of the total distance (D)  611 , ‘x 0 ’  609 , and the angle θ  607 , the transverse particle position y  613  may be obtained.
 
       FIG. 6B  shows an alternative geometrical confirmation of the beam pattern  600   b  that may be used for finding the transverse particle position y  613 . The beam pattern  600   b  comprises a majority of the geometrical relationships of the previous beam pattern  600   a  with a few differences. In beam pattern  600   b , the label ‘x 0 ’  633  represents the smallest distance a particle may pass through the first region  601  before reaching a center  634  of the second region  603 . The label ‘x’  643  is the distance between the center  634  and an intersection center  635 . The intersection center  635  may represent a location where the particle, traveling in the particle path  612 , intersects with the center of the second region  603 . The label ‘vT 1 ’ is a mathematical expression representing the total distance traveled in the first region  601  through the center of the second region  603 , with timing signal T 1    639  representing the time of travel. The timing signal T 2    641  represents the remaining time of travel, or the time of travel between the center of the second region  603  through the end of the third region  605 . T 2    641  may be obtained from a graph similar to the graph  527  shown in  FIG. 5C  (i.e., T 2 =t 2 /2). 
     Using the mathematical relationships of equations (1)-(8), a value for the transverse particle position y  613  may be obtained for the configuration of pattern  600   b : 
                   y   =       (         DT   1     T     -     x   0       )     ⁢     tan   ⁡     (   θ   )                 (   9   )               
It should be appreciated that any other geometrical pattern configuration may be employed in the determination of the transverse particle position y  613  from timing measurements. Additionally, it should be appreciated that the light beam pattern need not have sharp edges or a binary intensity profile, as shown in  FIGS. 6A and 6B . It is only required that the light beam pattern provides distinct timing signals for transverse particle paths separated by resolution distances of interest.
 
       FIG. 7  shows a depiction of a particle detection system  700  capable of producing two particle positions, one position in a transverse position (the y, or third, dimension) and a particle position in a longitudinal direction (the z, or first, dimension).  FIG. 8  shows a flow diagram  800  of an overview of operations that may be taken by the detection system  700 . It should be appreciated that the operations described in  FIG. 3  are also performed in the detection system  700  of  FIG. 7 . 
     Referring to  FIG. 7 , the particle detection system  700  includes a light source  701  configured to produce a propagating light beam  703  in the z, or first, dimension in this example embodiment. The light source  701  may be coupled to a masking element  705 , such that once the light source  701  illuminates the masking element  705 , a light beam pattern  707  is produced in the propagating beam  703  in the x, or second, and y, or third, dimensions. The propagating beam  703  comprising the light pattern  707  may be configured to intersect a sample volume  709  through which a particle flow flows in the x, or second, dimension. As the particles in the sample volume  709  pass through the light beam pattern  707  of the propagating beam  703 , a diverging scattered light  711  may be produced. Similar to the light scattering  211  of  FIG. 2 , the diverging light scattering  711  defines a temporal profile. The temporal profile has defined therein timing values indicative of the particle&#39;s position, in the sample volume  709 , in the y, or third, dimension. The diverging scattered light  711  and the propagating beam  703  may be passed through an optical focusing element  713 , resulting in a converging scattered light  717 . The patterned beam  703  may be blocked by a light beam block  715  in order to prevent a first light detector  719  from receiving the beam  703 , thus reducing the risk of detector saturation. The converging scattered light  717  may be focused onto the light detector  719 . 
     The particle detection system  700  may also include a second light source  721  that may be configured to produce a propagating beam  723  in a y, or third, dimension. The light source  721  may be coupled to a masking element  725  in order to produce a light beam pattern  727  in the propagating beam  723  in the x, or second, and z, or first, dimensions ( FIG. 8 ,  801 ). The propagating beam  723  may then be passed through the sample volume  709 . Once the particles in the sample volume  709  pass through the light pattern  727  in the propagating beam  723 , a diverging scattered light  729  may be produced. An optical focusing element  731  may be used to focus the pattern beam  723  onto a light beam block  733 , thus preventing a saturation of a second light detector  737 . The focusing element  731  may also be used to focus the diverging scattered light  729 , resulting in converging scattered light  735 . The converging scattered light  735  may define a temporal profile. The temporal profile may include timing values indicative of the particle&#39;s position, in the sample volume  709 , in the z, or first, dimension. The converging scattered light  735  may be focused onto the second light detector  737  in order to detect the temporal profile provided by the scattering light  735  ( FIG. 8 ,  803 ). 
     The light detectors  719  and  737  may be coupled to a processing unit  739 . The light detectors  719  and  737  may be configured to send data measurements  741  and  743 , respectively, to the processing unit  739 . The processing unit  739  may be configured to determine the position of the particle in a y, or third, dimension in the sample volume  709  using the measurement data  741  provided by the first light detector  719 . The processing unit  739  may also be configured to measure the position of the particle in the z, or first, dimension in the sample volume  709  using the measurement data  743  provided by the second light detector  737  ( FIG. 8 ,  805 ). The processing unit  739  may be configured to send measurement instructions  745  and  747  to the light detectors  719  and  737 , respectively. The instructions  745  and  747  may, for example, include on/off instructions. A data link  749  between the light detector  737  and the processing unit  739  and a data link  751  between the light detector  719  and the processing unit  739  may be any form of data transmission link known in the art. It should also be appreciated that the database and network connections of  FIG. 2  may also be employed in the particle detection system  700  shown in  FIG. 7 . 
     It should also be appreciated that the masking element described in reference to  FIGS. 2 ,  4 , and  7  herein may, as an alternative to producing intensity variation, produce a beam pattern with portions of varying polarization. 
       FIG. 9  shows a masking element  900  comprising a polarization inducing section  901  configured to produce a beam pattern comprising portions of varying polarization. 
       FIG. 10  is an example of a particle detection system  1000  capable of obtaining a particle position in a transverse, or y (third), dimension and a longitudinal direction, or z (second), dimension. The particle detection system  1000  may include a first light source  1001  configured to produce a propagating beam  1003  in the z, or first, dimension. The light source  1001  may be coupled to a polarizing element  1005 . The polarizing element  1005  may be coupled to a first polarization processor  1007 . The first polarization processor  1007  may provide polarization instructions  1009  to the polarizing element  1005 . The polarizing element  1005  may induce a first polarization  1111  in the propagating beam  1003 . A masking element  1113  may also be coupled to the light source  1001 , in order to produce a light beam pattern  1114 , in the x, or second, and y, or third, dimensions, in the propagating beam  1003 . The propagating beam  1003  may be configured to pass through a sample volume  1115 , comprising a particle flow in an x, or second, dimension. 
     As a result of the particles in the sample volume  1115  passing through the light beam pattern  1114  of the propagating beam  1003 , a diverging scattered light  1117  is produced. The diverging scattering light  1117  may define a temporal profile. The temporal profile may be used to determine timing signals that are, in turn, used to determine a particle location in a y, or third, dimension. An optical focusing element  1119  may be configured to focus the diverging scattering light  1117  resulting in a converging scattering light  1121 . The converging scattering light  1121  may be configured to pass through a first polarizer  1123  resulting in a filtration of the converging scattering light  1121 , thus allowing only light having the first polarization  1111  to be passed through and focused on a first light detector  1125 . Since the scattered light is focused off-axis with respect to the propagating beam  1003 , a beam block is not needed in this configuration. 
     The particle detection system  1000  may also include a second light source  1127  configured to produce a propagating beam  1129  in a y, or third, dimension. The light source  1127  may be coupled to a second polarizing element  1131 . The second polarizing element  1131  may be coupled to a second polarization processor  1133 . The second polarization processor  1133  may provide polarization instructions  1135  to the second polarizing element  1131 . The polarization instructions  1135  may be used by the second light source  1127  to produce a second polarization  1137  in the propagating beam  1129 . A masking element  1139  may be coupled to the light source  1127  in order to produce a second light beam pattern  1140 . The propagating beam  1129 , comprising the light beam pattern  1140  and the second polarization  1137 , may be configured to pass through the sample volume  1115 . 
     As the particles in the sample volume  1115  pass through the light beam pattern  1140  a diverging scattering light  1141  may be produced. A second optical focusing element  1143  may be configured to focus the diverging scattering light  1141 , resulting in a converging scattering light  1145 . The converging scattering light  1145  may be configured to pass through a second polarizer  1147 , thus resulting in the filtering of the converging scattering light  1145  and, therefore, allowing only light featuring the second polarization  1137  to pass through. The filtered light is then focused onto a second light detector  1149 . Since the scattered light is focused off-axis with respect to the propagating beam  1129 , a beam block is not needed in this configuration. 
     The particle detection system  1000  may also employ a processing unit  1151  coupled to the first light detector  1125  and the second light detector  1149 . The first and second light detectors  1125  and  1149 , respectively, may provide data measurements  1153  and  1155 , respectively, to the processing unit  1151 . The processing unit  1151  may be configured to determine a particle position in the y, or third, and z, or first, dimensions using the supplied data measurements  1153  and  1155 , respectively. The determined particle positions may be based on timing signals obtained from the respective temporal profiles. The processing unit  1151  may also provide measurement instructions  1157  and  1159  to the first and second light detectors  1125  and  1149 , respectively via communications links  1158 ,  1161 . The instructions  1157  and  1159  may comprise on/off instructions. 
     The processing unit  1151  may also be coupled to the first and second polarization processing units  1007  and  1133 , of the first and second light sources  1001  and  1127 , respectively. The processing unit  151  may provide a polarization request  1163  and  1165  to the first and second polarization processing units of the first and second light sources, respectively. The polarization requests  1163  and  1165  provide polarization settings for the light sources  1001  and  1127 , respectively. The first and second polarization processing units of the first and second light source  1007  and  1133 , respectively, may also provide a polarization status  1167  and  1169 , respectively, to the processing unit  1151 . The polarization status  1167  and  1169  may provide a current polarization setting of the polarizing elements  1005  and  1131 , respectively. It should be appreciated that the database and networking connections shown in  FIG. 2  may also be implemented in the particle detection system  1000  of  FIG. 10 . 
       FIG. 11  illustrates another configuration of a particle detection system  1181  which may provide a particle position in a transverse (y), or third, dimension, and in a longitudinal (z), or first, dimension. In contrast to the detection systems shown in  FIGS. 7 and 10 , the detection system  1181  may be configured to use a single light detector  1225 . The detection system  1181  may employ a first light source  1183  configured to provide a propagating beam  1185  in the z, or first, dimension. A coding element  1187  may be coupled to the first light source  1183 . In the configuration shown in  FIG. 11 , the coding element  1187  may be a modulator configured to provide temporal modulation, resulting in a frequency setting (f 1 ) induced in the first light source  1183 . Thus, the illumination of the beam  1185  includes a first frequency  1193 . A processor  1189  may be coupled to the first coding element  1187  in order to provide frequency settings  1191 . A masking element  1195  may be coupled to the first light source  1183  in order to provide a light beam pattern  1197  in the x, or second, and y, or third, dimensions, in the propagating beam  1185 . The propagating beam  1185  comprising the light beam pattern  1197 , and illuminating at a first frequency  1193  may be configured to pass through a sample volume  1199  comprising a flow of particles in an x, or second, dimension. 
     The particle detection system  1181  may also comprise a second light source  1203  configured to provide an illuminating beam  1205  in the y, or third, dimension. A second coding element  1207  may be coupled to the second light source  1203  in order to provide a second frequency (f 2 )  1213  to the illuminating beam  1205 . A second modulation processor  1209  may be coupled to the second coding element  1207  in order to provide frequency setting  1211 , providing a value of the second frequency  1213 . A masking element  1215  may be coupled to the second light source  1203  in order to provide a second light beam pattern  1217  in a z, or first, and x, or second, dimensions. The propagating beam  1205 , comprising the light beam pattern  1217  and illuminating at a second frequency  1213 , may be configured to pass through the sample volume  1199  with the particle flow in an x, or second, dimension. 
     As the particles in the sample volume  1199  pass through the light beam patterns  1197  and  1217  of the propagating beams  1185  and  1205 , respectively, a combined diverging scattering light  1219  is produced. The diverging scattering light  1219  defines a temporal profile comprising position information about the particles in the z, or first, and y, or third, dimensions, in the sample volume  1199 . The light scattering produced by the first light beam pattern  1197  may produce information indicative of a particle position in the y, or third, dimension. The light scattering produced by the second light beam pattern  1215  may produce information indicative of a particle position in the z, or first, dimension. 
     An optical focusing element  1221  may be configured to focus the diverging scattering light  1219 , resulting in a converging scattering light  1223 . The converging scattering light  1223  is focused onto a light detector  1225 . First and second bandpass filters  1229  and  1231 , respectively, may be coupled to the light detector  1225 . In this example embodiment, the light detector  1225  sends measured data  1227  to the first and second bandpass filters  1229  and  1231 , respectively. The first bandpass filter  1229  may be configured to filter out all data in the measured signal  1227  not having information of the first frequency  1193 . Similarly, the second bandpass filter  1231  may be configured to filter out all data in the measured signal  1227  not having information of a second frequency  1213 . 
     A processing unit  1233  may be coupled to the first and second filters  1229  and  1231 , respectively. In this example embodiment, the first and second bandpass filters  1229  and  1231 , respectively, are configured to provide filtered measurement data  1235  and  1237 , respectively, to the processing unit  1233 . The processing unit  1233  may be configured to determine a particle position in the y, or third, and z, or first, dimensions using the filtered data  1235  and  1237 , respectively. The determined particle positions may be based on timing signals obtained from the temporal profile. The processing unit  1233  may be configured to provide filtering or detection instructions  1239  and  1241  to the first and second filters  1229  and  1231 , respectively. The filtering instructions  1239  and  1241  may include on/off commands as well as frequency detection settings. 
     The processing unit  1233  may also be coupled to the first and second modulation processors  1189 ,  1209  of the first and second light sources  1183  and  1203 , respectively. The processing unit  1233  may send coding instructions  1247  and  1249  to the first and second modulation processors  1189  and  1209 , respectively. The coding instructions  1247  and  1249  may contain frequency settings used to program the first and second coding elements  1187  and  1207 , respectively. The first and second modulation processors  1189  and  1209  may be configured to send a coding status  1251  and  1253 , respectively, to the processing unit  1233 . The coding status  1251  and  1253  may comprise information of a current frequency setting. It should be appreciated that the particle detection system  1181  may also employ the database and network configurations shown in  FIG. 2 . 
       FIG. 12A  illustrates a particle detection system  1261  capable of determining a particle position in a transverse (y), or third, dimension, and a longitudinal (z), or first, dimension. The particle detection system  1261  may employ a first light source  1263  configured to provide a propagating beam  1265  in the z, or first, dimension. A first coding element  1267  may be coupled to the first light source  1263 . A first coding processor  1269  may be coupled to the first coding element  1267  in order to provide coding instructions  1271 . In the example shown in  FIG. 12A , the coding instructions may be wavelength instructions used for selecting an illumination wavelength of the first light source  1263 . A masking element  1275  may be coupled to the first light source  1263  in order to provide a light beam pattern  1277  in the y, or third, and x, or second, dimensions. The propagating beam  1265 , comprising the selected wavelength  1273  and light beam pattern  1277 , may be configured to pass through a particle flow in a sample volume  1279 . As the particles in the sample volume  1279  pass through the light beam pattern  1277 , a diverging scattering light  1281  is produced. The diverging scattering light  1281  may be configured to pass through a first filter  1283  allowing light of only the selected wavelength  1273  to pass through. An optical focusing element  1285  may be configured to focus the diverging scattering light  1281  resulting in converging scattering light  1287  focused onto a light detector  1289 . 
     The particle light detection system  1261  may also employ a second light source  1291  configured to provide a propagating beam  1293  in the y, or third, dimension. A second coding element  1295  may be coupled to the second light source  1291 . A second coding processor  1297  may be coupled to the second coding element  1295  in order to provide coding instructions  1299 . The coding instructions  1299  may include wavelength illumination instructions used in selecting a second wavelength  1301  for an illumination produced by the second light source  1291 . A masking element  1303  may be coupled to the second light source  1291  in order to produce a second light beam pattern  1305  in the z, or first, and x, or second, dimensions. The propagating beam  1293 , including the second selected wavelength  1301  and the second light beam pattern  1305 , may be configured to pass through the sample volume  1279 . As the particles in the sample volume  1279  pass through the second light beam pattern  1305 , a second diverging scattering light  1307  may be produced. A second filter  1309  may be configured to filter the diverging scattering light  1307 , such that only light comprising the second selected wavelength  1301  may pass. A second optical focusing element  1311  may be configured to focus the diverging scattering light  1307  resulting in a converging scattering light  1313  being focused on a second light detector  1315 . 
     The particle detection system  1261  may also comprise a processing unit  1317  coupled to the first and second light detectors  1289  and  1315 , respectively. The processing unit  1317  may be configured to provide measurement instructions  1319  and  1325  to the first and second particle detectors  1289  and  1315 , respectively. The measurement instructions  1319  and  1325  may provide on/off commands or wavelength detection settings. The first and second light detector  1289  and  1315  may be configured to provide data measurements  1323  and  1325 , respectively, to the processing unit  1317 . The processing unit  1317  may be configured to determine a particle position in the y, or third, and z, or first, dimensions using the supplied data measurements  1323  and  1325 , respectively. The determined particle positions may be based on timing signals obtained from the respective temporal profiles. The processing unit  1317  may also be coupled to the coding processors of the first and second light sources  1269  and  1297 , respectively. The processing unit  1317  may provide coding instructions  1331  and  1333  to the first and second coding processors  1269  and  1297 , respectively. The first and second coding processors  1269  and  1297  may provide a coding status  1335  and  1337 , respectively, to the processing unit  1317 . It should be appreciated that the database and network connections of  FIG. 2  may also be incorporated into the particle detection system  1261 . It should also be appreciated that data transmission links  1339 ,  1341 ,  1327 , and  1329  may comprise any data transmission link known in the art. 
       FIG. 12B  provides an alternative configuration  1345  of the particle detection system shown in  FIG. 12A . The alternative configuration  1345  provides a more compact system. Instead of employing two filters, as shown in the particle system  1261 , a single dichroic filter  1353  may be used. Thus, as the particles in the sample volume  1279  pass through the light beam patterns  1277  and  1303 , a combined diverging scattering light  1347  is produced. The combined scattering light  1347  may define a temporal profile indicative of a particle position in the z, or first, dimension, and y, or third, dimension. The temporal profile may provide timing signals indicative of particle position to be used by the processing unit  1317 . 
     An optical focusing element  1349  may be used to focus the combined diverging scattering light  1347  in order to produce a converging scattering light  1351 . Upon passing the dichroic filter  1353 , the converging scattering light  1351  may be decomposed into a first converging scattering light  1355  of the first selected wavelength  1273  and a second converging scattering light  1357  of the second selected wavelength  1301 . The first filtered scattering light  1355  may be focused onto a first light detector  1289  and the second scattering light  1357  may be focused onto the second light detector  1315 . 
       FIG. 13A  provides illustrations of a particle detection system  1361  in examples a-d that may provide a longitudinal particle position in a z, or first, dimension.  FIG. 14  provides a flow diagram describing an overview the operations taken by the particle detection system  1361 . Referring to  FIGS. 13A and 14 , in the first particle detection system  1361   a , an illumination beam  1365  may be configured to travel in the z, or first, dimension ( FIG. 14 ,  1401 ). The illumination beam  1365  may further be configured to intersect a sample volume  1363  through which particles traveling in an x, or second, dimension travel. The particles may travel, for example, in a top path  1364   a , center path  1364   b , or bottom path  1364   c . The top, center and bottom paths represent different positions of the particle in the z, or first, dimension. 
     As the particle travels in the x, or second, dimension and passes through the illumination beam  1365 , a diverging scattering light  1367  may be produced ( FIG. 14 ,  1405 ). The diverging scattering light  1367  may define a temporal profile that may, by the scattering, further include information indicative of the particle position in the z, or first, dimension. An optical focusing element  1369  may be configured to focus the diverging scattering light  1367 , resulting in a converging scattering light  1370 . A light blocker  1371  may be used to block the illumination beam  1365 , thus preventing a photodetector  1375  from “seeing” the illumination beam  1365 , and, therefore, preventing detector saturation. The converging scattering light  1370  may be focused onto a patterned optical block  1373   a ,  1373   b ,  1373   c  placed in front of the detector  1375  ( FIG. 14 ,  403 ). The optical block  1373   a - c  may include three sections, for example, a top section  1373   a , center section  1373   b , and bottom section  1373   c . The top and bottom sections of the optical block  1373   a ,  1373   c  may use blocking sections  1374  and  1376 , respectively, which may partially or completely block the scattering light  1370  from reaching the photodectector  1375  ( FIG. 14 ,  1407 ). Measuring a relative amount of light blocked by the blocking patterns  1374  and  1376 , with respect to an amount of unblocked light, may provide information about where the particle is traveling in the z, or first, dimension ( FIG. 14 ,  1409 ). 
       FIG. 13B  provides an example of measured signals which may be obtained using the particle detection system  1361 . The top path signal  1384  provides an example signal that may be obtained from a particle traveling along the top path  1364   a , as shown in the system in  FIG. 13A . As shown in  FIG. 13A , a particle traveling along the top path  1363   a  results in a converging scattering light  1370  that is focused on the top layer of the optical block  1373   a , while the light scattering may be transmitted through the center and bottom layers of the optical beam block  1373   b  and  1373   c , respectively. Therefore, the top path signal  1384  includes a “clear blocking” section  1385 , indicating that the particle has traveled along the top path  1364   a . If the particle has traveled only along the top path  1364   a , then only the top path signal  1384  may includes the clear blocking portion  1385 . As illustrated in  FIG. 13B , the center and bottom path signals  1387  and  1390 , respectively, do not have a clear blocking section  1385  if the particle is traveling along the top path  1364   a.    
     As also illustrated in  FIG. 13A , if a particle is traveling along the bottom path  1364   c  of the sample volume  1363 , then only the bottom path signal  1390  includes a clear blocking portion  1392 . If the particle is traveling along the center path  1364   b  of the sample volume  1363 , then neither the top nor bottom path signal  1384 ,  1390  has a blocking portion. Based on which signal  1384 ,  1387 ,  1390 , a determination can be made as to which path  1384   a - c  the particle traveled. 
     As is shown in  FIG. 13B , a particle traveling in the top portion, regardless of its position in the x, or second, dimension, may produce scattered light that only focuses on the top portion of the optical block  1373   a , thus being “transparent” to the middle and bottom portions of the optical block  1373   b  and  1373   c , respectively. Similarly, as seen in the particle detection systems  1361 , example c, a particle traveling in the bottom path  1364   c  of the sample volume  1363  may produce scattering light  1381  that may only be focused on the bottom layer of the optical block  1373   c . Therefore, the produced scattered light  1380  may be capable of being transmitted through the top and middle layers of the optical block  1373   a  and  1373   b , respectively. As seen from the optical particle system  1361 , example d, the particle traveling in the bottom path, regardless of its position in the x, or second, dimension, is only focused on the bottom layer of the optical beam block  1376 . 
       FIG. 15A  shows a particle detection system similar to that of  FIG. 13A , with the particle detection system in  FIG. 15A  employing a pattern light block  1513  with an alternative blocking pattern. The blocking pattern of optical block  1513  includes blocking edges, rather than the blocking regions of optical block  1373   a - c  of  FIG. 13A .  FIG. 15B  provides example measurement signals which may be obtained from the particle detection system of  FIG. 15A  through use of the alternative blocking pattern of the optical block  1513 . A particle traveling in the top path  1504   a  of the particle path  1503  may only be focused on a top portion  1514   a  of the optical block  1513 . The resulting signal  1517  may comprise a completely blocked portion  1519  of a first portion of the obtained signal and an unblocked portion  1521  in a second portion of the signal  1517  indicative of the particle traveling in the top path  1504   a . A particle traveling in the bottom path  1504   c  of the particle path  1503  may only be focused on the bottom portion  1514   c  of the optical block  1513 . The resulting signal  1527  may represent an unblocked region  1529  in a first portion of the signal and a blocked region  1531  in a second portion of the signal. Finally, a particle traveling in the center path  1504   b  may only be focused in the center portion  1514   b  of the optical block  1513 . The resulting signal  1523  may not comprise any portions indicative of a blocked signal, but only a portion representing an unblocked signal  1523 . 
       FIG. 16  provides an example of a particle detection system  1600  capable of providing two particle positions in a longitudinal (z), or first, dimension, and a transverse (y), or third, dimension. The particle detection system  1600  may include a light source  1601  configured to provide a propagating beam  1603  propagating in the z, or first, dimension. A masking element  1605  may be coupled to the light source  1601  and may be configured to produce a light beam pattern  1607  in an x, or second, and y, or third, dimension, in the propagating beam  1603 . As the propagating beam  1603 , defining the light pattern  1607 , is passed through a sample volume  1609  comprising particles, the particles passing through the light beam pattern  1607  may produce diverging scattering light  1611 . An optical focusing element  1613  may be used to focus the diverging scattering light  1611 , therefore producing converging scattering light  1617 . An optical blocker  1615  may be used to block the illuminating beam  1603 , thus preventing the light detector  1625  from receiving light from the illuminating beam  1603  and becoming saturated. The converging scattering light  1615  may be configured to pass through an optical beam block  1619 . Upon passing through the optical beam block  1619 , a partially blocked scattered light  1621  may be configured to be detected by the light detector  1623 . 
       FIG. 17  is a depiction of a flow diagram  1700  of an overview of the operations that may be taken by a processing unit  1625 . The processing unit  1625  may be coupled to the light detector  1623 . The light detector  1623  may provide data measurements  1629  to the processing unit  1625  ( 1701 ). The processing unit  1625  may provide measurement instructions  1631 , which may comprise on/off directions, to the light detector  1623 . 
     Using the temporal profile, the processing unit  1625  may process the profile in order to obtain multiple timing values, similar to the timing signals discussed in relation to  FIGS. 5B ,  5 C,  6 A, and  6 B ( 1703 ). The processing unit  1625  may further be configured to determine a position of the particle in a transverse (y), or third, dimension using the timing values obtained from the temporal profile ( 1705 ). 
     Using blocking information obtained from the optical block  1619 , the processing unit  1625  may be configured to measure a relative amount of light blocked from the blocking regions of the light block, with respect to an amount of light unblocked by the plurality of blocking regions ( 1707 ). The processing unit may be further configured to determine a position of the particle in the longitudinal (z), or first, dimension, based on the relative amount of light blocked ( 1709 ). It should be appreciated that the processing unit  1625  may comprise the database and network configurations shown in  FIG. 2 . 
       FIG. 18  provides an example of a measurement signal  1819  which may be obtained from the particle detection system of  FIG. 16 . The resulting measurement signal  1819  may be produced by the addition of the measurement signal obtained from the pattern beam  1801  and the measurement signal obtained from the optical pattern block  1809 . Similar to the measurement signal shown in  FIG. 5B , the measurement signal obtained from the patterned light beam  1801  may comprise three portions indicative of a time value representing the time the particle passed through the three sections of the pattern beam. In this example, t 1  represents the time the particle passed through the first section of the pattern beam, t 2  represents the time the particle passed through a second section of the pattern beam, and t 3  represents the time taken for the particle to pass through the third section of the pattern beam ( FIG. 5A ). 
     The measurement signal obtained by the pattern light block  1809  illustrates an example of a signal obtained from a particle traveling in the top path of the sample volume, as illustrated in  FIG. 13B . The exact particle location in the z, or first, dimension may be obtained empirically from the measured signal, for example in a similar manner as was previously described in relation to  FIG. 13B . The exact particle location in the z, or first, dimension may also be found quantitatively using the timing values t 4 -t 6 ,  1811 - 1817  respectively, and amplitudes a and b,  1813  and  1815  respectively. The quantitative method of finding the particle location in the z, or first dimension may rely not only on the timing values supplied by the temporal profile, but may also rely on the optical system that focuses the scattered light on to the patterned light block. 
       FIG. 19  illustrates an example application for which the particle position detection system may be used. Region  1901  illustrates a light beam  1903  that induces fluorescence in particles it illuminates and particles traveling in a top  1905   a , or a center  1905   b , or a bottom  1905   c  particle path. Fluorescent signals  1907 ,  1909 , and  1911  represent the measured signals obtained from identical particles traveling in the top, center, and bottom paths, respectively. As is shown in the figure, the signal obtained from the particle traveling in the center path  1909  provides the strongest signal, with the integration under the curve equaling, for example, 1.0. In contrast, the signals obtained from the top and bottom paths  1907  and  1911 , respectively, show weaker signals with the integration of both curves equaling, for example, 0.5. Thus identical particles traveling through different parts of the fluorescence inducing beam produce different amounts of fluorescence. This nonuniformity in signals confuses the discrimination of different types of particles. For example a big particle traveling through the edge of the fluorescence inducing beam may generate as much fluorescence signal as a small particle traveling through the center of the fluorescence inducing beam 
     Block  1913  represents the pattern beam  1915 , and the particle paths  1917   a - c , as was previously described in the system shown in  FIG. 2 . Using the information from the previously described particle detection system, it may be possible to determine where the particle is traveling in the fluorescent beam. As shown in region  1932  the fluorescent beam  1903  may be superimposed with the particle beam  1915 , thus, the two obtained measurements may be combined in order to find the exact location of the particle traveling through the fluorescent beam. Using the knowledge of the particle position, a normalization (or correction) factor may be compiled, such that the normalization factor may be multiplied by the weaker signals  1907  and  1911 . Therefore, the weaker signals may be normalized so that their integration values equals 1, resulting in a stronger signal reading as shown in the updated signals  1927 ,  1929  and  1931 . Such a calculation may be obtained from a calculation unit  1925 . This normalization removes the variation in fluorescence signals due to particle position and allows the remaining variations to be interpreted as variations in particle characteristics. 
     While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.