Raman probe having a small diameter immersion tip

1. An immersion probe for use in Raman spectroscopy which includes:

an extended immersion tip that includes an internally reflecting lightguide;

first optical element for collecting laser radiation emerging from a first optical fiber and directing it, after subsequent reflections, into the end of said internally reflecting lightguide in such a way that it is as nearly collimated as possible consistent with substantially all of the radiation entering the lightguide;

second optical element for collecting Raman shifted radiation emerging from said internally reflecting light guide and focusing it on a second optical fiber in such a way that the size and shape of the image of the end of the lightguide matches the size and shape of said second optical fiber;

reflecting means for redirecting the beam formed by said first optical element so that its axis is anti-parallel to and coaxial with the axis of the Raman shifted radiation emerging from said lightguide.

2. The immersion probe of claim 1 wherein the numeric apertures corresponding to the diameter and longitudinal positions of said first and second optical elements are at least as great as the numeric apertures of the associated optical fibers.

3. The immersion probe of claim 2 wherein the diameter of said second optical fiber is substantially greater than the diameter of said first optical fiber.

4. The immersion probe of claim 3 wherein the distance from said first optical element to said first optical fiber is set so that the image of said first optical fiber is falls at the end or within said lightguide and is no greater in diameter than said lightguide.

5. The immersion probe of claim 4 wherein the ratio of the distance from said first optical element to said first optical fiber to the distance from said first optical element to said lightguide is approximately equal to the diameter of said first optical fiber to the internal diameter of said lightguide, and

Wherein the ratio of the distance from said second optical element to said second optical fiber to the distance from said second optical element to said lightguide is approximately equal to the diameter of said second optical fiber to the internal diameter of said lightguide.

6. The immersion probe of claim 2 in which said reflecting means comprises two totally reflecting, parallel surfaces.

7. The immersion probe of claim 6 in which the area of the reflecting surface which overlaps the collected radiation is small compared to the cross section of said collected radiation in the vicinity of said reflecting surface.

8. The immersion probe of claim 7 in which said reflecting means is an internally reflecting rhomboid.

9. The immersion probe of claim 1 wherein the diameter of said second optical fiber is substantially greater than the diameter of said first optical fiber.

10. The immersion probe of claim 9 wherein the distance from said first optical element to said first optical fiber is set so that the image of said first optical fiber is falls at the end or within said lightguide and is no greater in diameter than said lightguide.

11. The immersion probe of claim 10 wherein the ratio of the distance from said first optical element to said first optical fiber to the distance from said first optical element to said lightguide is approximately equal to the diameter of said first optical fiber to the internal diameter of said lightguide, and

Wherein the ratio of the distance from said second optical element to said second optical fiber to the distance from said second optical element to said lightguide is approximately equal to the diameter of said second optical fiber to the internal diameter of said lightguide.

12. The immersion probe of claim 1 in which said reflecting means comprises two totally reflecting, parallel surfaces.

13. The immersion probe of claim 12 in which the area of the reflecting surface which overlaps the collected radiation is small compared to the cross section of said collected radiation in the vicinity of said reflecting surface.

14. The immersion probe of claim 13 in which said reflecting means is an internally reflecting rhomboid.

15. An immersion probe for use in Raman spectroscopy which includes:

an extended immersion tip that includes an internally reflecting lightguide;

first optical element for collecting laser radiation emerging from a first optical fiber and directing it, after subsequent reflections, into the end of said internally reflecting lightguide in such a way that it is as nearly collimated as possible consistent with substantially all of the radiation entering the lightguide;

second optical element for collecting Raman shifted radiation emerging from said internally reflecting light guide and focusing it on a second optical fiber in such a way that the size and shape of the image of the end of the lightguide matches the size and shape of said second optical fiber;

reflecting means for redirecting the beam formed by said second optical element so that its axis is anti-parallel to and coaxial with the axis of the Raman shifted radiation emerging from said lightguide.

16. The immersion probe of claim 15 wherein the numeric apertures corresponding to the diameter and longitudinal positions of said first and second optical elements are at least as great as the numeric apertures of the associated optical fibers.

17. The immersion probe of claim 16 wherein the diameter of said second optical fiber is substantially greater than the diameter of said first optical fiber.

18. The immersion probe of claim 17 wherein the distance from said first optical element to said first optical fiber is set so that the image of said first optical fiber is falls at the end or within said lightguide and is no greater in diameter than said lightguide.

19. The immersion probe of claim 18 wherein the ratio of the distance from said first optical element to said first optical fiber to the distance from said first optical element to said lightguide is approximately equal to the diameter of said first optical fiber to the internal diameter of said lightguide, and

Wherein the ratio of the distance from said second optical element to said second optical fiber to the distance from said second optical element to said lightguide is approximately equal to the diameter of said second optical fiber to the internal diameter of said lightguide.

20. The immersion probe of claim 16 in which said reflecting means comprises two totally reflecting, parallel surfaces.

21. The immersion probe of claim 20 is which the area of the reflecting surface which overlaps the collected radiation is small compared to the cross section of said collected radiation in the vicinity of said reflecting surface.

22. The immersion probe of claim 21 in which said reflecting means is an internally reflecting rhomboid.

23. The immersion probe of claim 15 wherein the diameter of said second optical fiber is substantially greater than the diameter of said first optical fiber.

24. The immersion probe of claim 23 wherein the distance from said first optical element to said first optical fiber is set so that the image of said first optical fiber is falls at the end or within said lightguide and is no greater in diameter than said lightguide.

25. The immersion probe of claim 24 wherein the ratio of the distance from said first optical element to said first optical fiber to the distance from said first optical element to said lightguide is approximately equal to the diameter of said first optical fiber to the internal diameter of said lightguide, and

Wherein the ratio of the distance from said second optical element to said second optical fiber to the distance from said second optical element to said lightguide is approximately equal to the diameter of said second optical fiber to the internal diameter of said lightguide.

26. The immersion probe of claim 15 in which said reflecting means comprises two totally reflecting, parallel surfaces.

27. The immersion probe of claim 26 in which the area of the reflecting surface which overlaps the collected radiation is small compared to the cross section of said collected radiation in the vicinity of said reflecting surface.

28. The immersion probe of claim 27 in which said reflecting means is an internally reflecting rhomboid.