Light collection from objects within a fluid column
An optical arrangement receives output light emanating from an object disposed within a fluid column that crosses an optical refraction boundary of the fluid column between the object and the optical arrangement. The optical arrangement modifies the output light such that the modified output light has an intensity that is more uniform than the output light.
1. A discrimination system comprising:
a measurement region configured to receive a flow stream comprising a core stream containing objects, the core stream being surrounded by a sheath stream that defines an optical refraction boundary;
an excitation source configured to generate excitation light directed towards the objects in the measurement region, the objects emanating output light in response to the excitation light;
an optical arrangement having an optical axis configured to receive and modify the output light emanating from the object disposed within a flow stream, the optical arrangement further comprising a mask for attenuating excitation light emanating from objects near the center of the flow stream, wherein the mask is configured to preferentially collect a first portion of the output light emanating from objects at larger angles with respect to the optical axis relative to a second portion of the output light emanating from the objects at smaller angles with respect to the optical axis;
an optical detector arranged to receive the modified output light, the optical detector configured to detect the modified output light and to provide an electrical signal responsive to the modified output light; 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.
2. The discrimination system of claim 1 , wherein the mask further comprises a plate that includes an aperture and an elongated mask feature disposed at least partially across the aperture, the elongated mask feature arranged such that a longitudinal axis of the elongated mask feature is substantially parallel to a direction of flow of the objects in the flow stream, the plate and the elongated mask feature being less transmissive to the output light than the aperture.
3. The discrimination system of claim 1 , wherein the mask is configured to preferentially attenuate output light received from a first position in the flow stream compared to output light received from a second position in the flow stream, wherein the second position is farther from the center of the flow stream than the first position along an axis perpendicular to the optical axis of the optical arrangement.
4. The discrimination system of claim 1 , wherein the mask comprises an elongated mask feature that attenuates the output light received from the first position, the elongated mask feature disposed proximate to an active area of the optical detector such that a longitudinal axis of the elongated mask feature is substantially parallel to a direction of flow of the objects in the flow stream.
5. The discrimination system of claim 4 , wherein the elongated mask feature has a round cross sectional area.
6. The discrimination system of claim 4 , wherein the elongated mask feature has a rectangular cross sectional area.
7. The discrimination system of claim 4 , wherein the elongated mask feature is a metal wire.
8. The discrimination system of claim 4 , wherein the elongated mask feature is a trace deposited on glass.
9. The discrimination system of claim 4 , wherein the elongated mask feature is a filament.
10. The discrimination system of claim 4 , wherein the elongated mask feature is an ink line printed on transparent paper.
11. The discrimination system of claim 4 , wherein the elongated mask feature is disposed at about a center of an active area of the detector.
12. A discrimination system comprising:
a measurement region configured to receive a flow stream comprising a core stream containing objects, the core stream being surrounded by a sheath stream that defines an optical refraction boundary;
an excitation source configured to generate excitation light directed towards the objects in the measurement region, the objects emanating output light in response to the excitation light;
an optical arrangement having an optical axis configured to receive and modify the output light emanating from the object disposed within a flow stream, the optical arrangement further comprising a mask for attenuating excitation light emanating from objects near the center of the flow stream, wherein the mask comprises a wire;
an optical detector arranged to receive the modified output light, the optical detector configured to detect the modified output light and to provide an electrical signal responsive to the modified output light; 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.
13. The discrimination system of claim 2 , wherein the plate and the elongated mask feature are one unitary structure.
14. The discrimination system of claim 2 , wherein the elongated mask feature is attached to the plate.
15. The discrimination system of claim 2 , wherein optical transparency of the plate to the output light varies as a function of position across the plate.
16. The discrimination system of claim 2 , wherein opposing longitudinal edges of the elongated mask feature are substantially parallel to one another.
17. The discrimination system of claim 2 , wherein opposing longitudinal edges of the elongated mask feature are not parallel to one another.
18. The discrimination system of claim 2 , wherein opposing longitudinal edges of the elongated mask feature are tapered along a longitudinal axis of the elongated mask feature.