Light collection from objects within a fluid column

1. A method, comprising:

receiving output light from an object in a fluid column, wherein the output light crosses an optical refraction boundary of the fluid column and the output light varies as a function of the object position in the fluid column;

generating an electrical signal in response to the output light;

compensating for position dependence of the object in the fluid column; and

distinguish between an object of a first type and an object of a second type.

2. The method of claim 1 , wherein the step of compensating for position dependence of the object in the fluid column comprises modifying the output light such that the modified output light has an intensity that is substantially uniform irrespective of a position of the object in the fluid column.

3. The method of claim 2 , further comprising:

attenuating a first portion of the output light received from a first position in the fluid column relative to a second portion of output light received from a second position in the fluid column, wherein the second position is farther from the center of the fluid column than the first position along an axis perpendicular to the optical axis of the optical apparatus

detecting the modified output light; and

generating an electrical signal in response to the modified output light.

4. The method of claim 3 , wherein the intensity of the modified output light is substantially uniform for objects across a cross section of the fluid column.

5. The method of claim 3 wherein the step of modifying the output light such that the modified output light has an intensity that is substantially uniform irrespective of a position of the object in the fluid column comprises incorporating a mask configured to attenuate light from the first position in the fluid column.

6. The method of claim 5 , wherein the mask comprises a wire.

7. The method of claim 5 , wherein the step of introducing a compensation that reduces or eliminates the variation in output light based on the object position in the fluid column further comprises incorporating an optical arrangement configured to preferentially collect a first portion of the output light emanating from the object at larger angles with respect to the optical axis relative to a second portion of the output light emanating from the object at smaller angles with respect to the optical axis.

8. The method of claim 7 , wherein the optical arrangement comprises a split objective lens configured to preferentially collect the first portion of the output light.

9. The method of claim 7 , wherein the optical arrangement further includes a mask configured to attenuate the second portion of the output light.

10. The method of claim 1 , wherein the object comprises a sperm cell.

11. A discrimination system, comprising:

an excitation light source configured to generate excitation light and to direct the excitation light toward an object in a fluid column, the object emanating output light in response to the excitation light wherein output light from the object in the fluid column varies as a function of the object position in the fluid column;

an optical arrangement configured to receive the output light, the output light crossing an optical refraction boundary of the fluid column between the object and the optical arrangement;

an optical detector configured to detect the output light and to provide an electrical signal responsive to the output light;

a compensation element that compensates for position dependence of the light emanating from the object; and

object type discrimination circuitry configured to discriminate between a first type of object and a second type of object based on the electrical signal.

12. The system of claim 11 , wherein the compensation element comprises an optical arrangement that produces a modified output light with an intensity that is substantially uniform irrespective of a position of the object within the fluid column.

13. The system of claim 11 , wherein the object type discrimination circuitry is configured to perform X/Y sperm cell discrimination.

14. The system of claim 12 , wherein the optical arrangement comprises a split objective lens configured to preferentially collect a first portion of the output light emanating from the object at higher angles with respect to the optical axis relative to collection of a second portion of the output light emanating from the object at lower angles with respect to the optical axis.

15. The system of claim 12 , wherein the optical arrangement comprises a mask configured to preferentially attenuate output light received from a first position in the fluid column compared to output light received from a second position in the fluid column, wherein the second position is farther from the center of the fluid column than the first position along an axis perpendicular to the optical axis of the optical arrangement.

16. The system of claim 12 , wherein the optical arrangement comprises an elongated mask feature that attenuates the output light received from the first position, a length of the elongated mask feature being much greater than a width of the elongated mask feature, the elongated mask feature disposed proximate to an active area of the detector such that a longitudinal axis of the elongated mask feature is substantially parallel to a direction of flow of the objects in the fluid column.

17. The system of claim 16 , wherein the elongated mask feature comprises one or more of the following features: a round cross sectional area, a rectangular cross sectional area, a metal wire, a trace deposited on glass, a filament, an ink line printed on transparent paper.

18. The system of claim 16 , wherein the elongated mask feature is disposed at about a center of an active area of the detector.