Absorption spectroscopy apparatus and method
An absorption spectroscopy apparatus including a sample cell having a central axis, and a side wall coaxially positioned about the axis. The side wall defines a generally circular cross-section of the cell as taken along a plane extending perpendicular to the axis, wherein the generally circular cross-section of the sample cell has an average radius. The side wall includes a plurality of light reflective segments arrayed about the axis, wherein each reflective segment has a cross-section taken along a plane extending perpendicular to the axis of the cell that is concave with respect to the axis. The concave cross-section of each segment has an average radius that is unequal to the average radius of the generally circular cross-section of the sample cell. Among other aspects and advantages, the apparatus of the present disclosure is able to use incoherent, non-collimated light sources while maintaining high optical throughput efficiencies.
1. An absorption spectroscopy apparatus comprising a sample cell including a central axis and a side wall coaxially positioned about the central axis and defining a generally circular cross-section of the sample cell as taken along a plane extending perpendicular to the axis of the cell, wherein the generally circular cross-section of the sample cell has an average radius, and wherein the side wall includes a plurality of light reflective segments arrayed about the axis, wherein each reflective segment has a cross-section taken along a plane extending perpendicular to the axis of the cell that is concave with respect to the axis, and the concave cross-section of each segment has an average radius that is unequal to the average radius of the generally circular cross-section of the sample cell.
2. An absorption spectroscopy apparatus according to claim 1 , wherein the average radii of the concave cross-sections of the segments of the side wall are equal.
3. An absorption spectroscopy apparatus according to claim 2 , wherein the average radii of the concave cross-sections of the segments of the side wall are each greater than the average radius of the generally circular cross-section of the sample cell.
4. An absorption spectroscopy apparatus according to claim 3 , wherein the average radii of the concave cross-sections of the segments of the side wall are each at least two times greater than the average radius of the generally circular cross-section of the sample cell.
5. An absorption spectroscopy apparatus according to claim 1 , wherein the average radii of the concave cross-sections of the segments of the side wall each comprises a constant radius.
6. An absorption spectroscopy apparatus according to claim 1 , wherein each of the average radii of the concave cross-sections of the reflective segments of the side wall pass through the axis of the sample cell.
7. An absorption spectroscopy apparatus according to claim 1 , wherein the light reflective segments of the side wall are equally arrayed about the axis.
8. An absorption spectroscopy apparatus according to claim 1 , wherein each of the reflective segments of the side wall of the cell has a cross-section taken along a plane extending parallel to the axis of the cell that is planar.
9. An absorption spectroscopy apparatus according to claim 1 , wherein each of the reflective segments of the side wall of the cell has a cross-section taken along a plane extending parallel to the axis of the cell that is concave with respect to the axis.
10. An absorption spectroscopy apparatus according to claim 9 , wherein at least one of the segments of the side wall includes a light transparent portion for admitting a ray of light directed into the cell and for allowing a ray of light to be directed out of the cell, and wherein the light transparent portion is located nearer to one end of the segment.
11. An absorption spectroscopy apparatus according to claim 1 , further comprising an optical gas sensor located within the cell and including an emitter for generating a ray of light and directing the ray of light to one of the reflective segments of the side wall of the cell, and a detector for receiving the ray of light from one of the reflective segments of the side wall of the cell.
12. An absorption spectroscopy apparatus according to claim 1 , wherein the side wall further includes at least one light-transparent segment and the apparatus further comprises at least one launch/collection reflector adapted to direct light through the light-transparent segment and into the cell and receive light directed out of the light-transparent segment from the cell.
13. An absorption spectroscopy apparatus according to claim 12 , wherein the launch/collection reflector comprises separate source and collection reflectors.
14. An absorption spectroscopy apparatus according to claim 12 , wherein the launch/collection reflector has a concave cross-section as viewed from an end of the launch/collection reflector.
15. An absorption spectroscopy apparatus according to claim 12 , wherein the launch/collection reflector has a concave cross-section as viewed from a side of the launch/collection reflector.
16. An absorption spectroscopy apparatus according to claim 12 , further comprising an emitter for generating a ray of light and directing the ray of light to the launch/collection reflector, and a detector for receiving the ray of light from the launch/collection reflector.
17. An absorption spectroscopy apparatus according to claim 12 , further comprising an emitter for generating a ray of light and directing the ray of light to the launch/collection reflector, and a detector for receiving the ray of light from the launch/collection reflector, and wherein the emitter comprises a wide angle, low frequency thermal emitter and the detector comprises a wide angle, low frequency thermal detector.
18. An absorption spectroscopy apparatus according to claim 1 , further comprising end walls closing ends of the side wall of the cell.
19. An absorption spectroscopy apparatus according to claim 18 , wherein the end walls have reflective surfaces facing inwardly with respect to the cell.
20. An absorption spectroscopy apparatus according to claim 18 , wherein the end walls include a fluid inlet and a fluid outlet.
21. An absorption spectroscopy apparatus according to claim 1 , wherein:
each of the reflective segments of the side wall of the cell has a cross-section taken along a plane extending parallel to the axis of the cell that is concave with respect to the axis;
at least one of the reflective segments of the side wall includes a light transparent portion for admitting a ray of light directed into the cell and for allowing a ray of light to be directed out of the cell, and wherein the light transparent portion is located nearer to one end of the segment;
the apparatus further comprises at least one launch/collection reflector adapted to direct light through the light transparent portion of the cell and receive light directed out of the light transparent portion of the cell; and
wherein the launch/collection reflector are positioned to direct a beam of light through the light transparent portion such that the beam is oriented at an angle other than perpendicular with respect to the axis of the cell.