Method and apparatus for conducting Raman spectroscopy

• US 7,636,157 B2
• Filed: 04/29/2005
• Issued: 12/22/2009
• Est. Priority Date: 04/30/2004
• Status: Active Grant

• Current Assignee: Ahura Scientific, Inc. (Thermo Fisher Scientific Incorporated)
• Original Assignee: Ahura Scientific, Inc. (Thermo Fisher Scientific Incorporated)
• Inventors: Azimi, Masud, Knopp, Kevin J., Wang, Peidong, Vakhshoori, Daryoosh, Shen, Yu
• Primary Examiner(s): Geisel; Kara E
• Application Number:
  US11/117,940
• Publication Number:
  US 20050248759A1
• Time in Patent Office: 1,698 Days
• Field of Search: 356/301
• US Class Current: 356/301
• CPC Class Codes: G01J 2003/1213 Filters in general, e.g. dichroic, band
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0218 using optical fibers
• CPC Class Codes: G01J 3/0272 Handheld
• CPC Class Codes: G01J 3/0291 Housings; Spectrometer accessories; Spatial arrangement of elements, e.g. folded path arrangements
• CPC Class Codes: G01J 3/44 Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
• CPC Class Codes: G01N 2021/656 Raman microprobe
• CPC Class Codes: G01N 21/65 Raman scattering

Abstract

Disclosed herein are Raman probes that include: (a) a first optical fiber for receiving laser excitation light from a light source and transmitting the same; (b) a first filter for receiving light from the first optical fiber and adapted to pass the laser excitation light and to block spurious signals associated with the light; (c) a second filter for receiving light from the first filter and adapted to direct the light toward a specimen; and (d) focusing apparatus for receiving the light from the second filter, focusing the light on the specimen so as to generate the Raman signal, and returning the Raman signal to the second filter. The second filter is further configured so that when the second filter receives the Raman signal from the focusing apparatus, the second filter filters out unwanted laser excitation light before directing the Raman signal to a second optical fiber.

Claims

1. A Raman probe comprising:

a first optical fiber for receiving laser excitation light from a light source and transmitting the same;

a first spectral filter for receiving light from the first optical fiber and adapted to pass the laser excitation light and to block spurious signals associated with the light;

a second spectral filter for receiving light from the first spectral filter and adapted to direct the light toward a specimen;

focusing apparatus for receiving the light from the second spectral filter, focusing the light on the specimen so as to generate the Raman signal, and returning the Raman signal to the second spectral filter, wherein the second spectral filter is further configured so that when the second spectral filter receives the Raman signal from the focusing apparatus, the second spectral filter filters out laser excitation light before directing the Raman signal to a broadband reflector; and

a broadband reflector disposed between the second spectral filter and a second optical fiber,

wherein the broadband reflector is configured to receive the Raman signal from the second spectral filter, to reflect the Raman signal to the second optical fiber, and to transmit laser excitation light; and

wherein the second optical fiber receives the Raman signal from the broadband reflector and transmits the same to a light analyzer.

2. A Raman probe according to claim 1 further comprising a light source.

3. A Raman probe according to claim 2 wherein the light source comprises at least one 785 nm semiconductor laser with limited linewidth.

4. A Raman probe according to claim 3 wherein the light source has a linewidth <

0.2 nm FWHM.

5. A Raman probe according to claim 1 further comprising a lens disposed between the first fiber and the first filter for collimating light from the first fiber on the first filter.

6. A Raman probe according to claim 1 wherein the spurious signals associated with the light comprise spurious signals associated with a laser that produces the laser excitation light, the fiber, and/or both.

7. A Raman probe according to claim 6 wherein the spurious signals associated with the laser comprise amplified spontaneous emission.

8. A Raman probe according to claim 1 wherein the spurious signals associated with the light comprise spurious signals associated with the fiber.

9. A Raman probe according to claim 8 wherein spurious signals associated with the fiber comprise fluorescence.

10. A Raman probe according to claim 8 wherein the spurious signals associated with the fiber comprise Rayleigh and Raman scatterings.

11. A Raman probe according to claim 1 wherein the spurious signals associated with the light comprise spurious signals associated with both a laser that produces the laser excitation light and the fiber.

12. A Raman probe according to claim 1 wherein the first filter is adapted to block amplified spontaneous emission from a laser that produces the laser excitation light and fluorescence and Rayleigh and Raman scatterings generated inside the first fiber.

13. A Raman probe according to claim 1 wherein the first filter comprises a bandpass filter.

14. A Raman probe according to claim 13 wherein the bandpass filter comprises a plurality of bandpass filter units working in combination with one another.

15. A Raman probe according to claim 1 wherein the first filter is adapted to filter out amplified spontaneous emission background in the Raman domain of>

300 cm<sup>−

1</sup>.

16. A Raman probe according to claim 1 wherein the second filter comprises a plurality of filter units working in combination with one another.

17. A Raman probe according to claim 16 wherein the second filter comprises three or more filter units working in combination with one another.

18. A Raman probe according to claim 1 wherein the second filter comprises a filter unit working in combination with a reflector unit.

19. A Raman probe according to claim 1 wherein a normal to a surface of the second filter is oriented at an angle of 22.5 degrees with respect to an optical path of the Raman signal between the specimen and the second filter.

20. A Raman probe according to claim 1 wherein a normal to a surface of the second filter is oriented at an angle of 5 degrees with respect to an optical path of the Raman signal between the specimen and the second filter.

21. A Raman probe according to claim 1 wherein a normal to a surface of the second filter is oriented at an angle of 10 degrees with respect to an optical path of the Raman signal between the specimen and the second filter.

22. A Raman probe according to claim 1 wherein the second filter comprises a long-pass filter.

23. A Raman probe according to claim 22 wherein the long-pass filter is adapted to filter out the amplified spontaneous emission background in the Raman domain of>

300 cm<sup>−

1</sup>.

24. A Raman probe according to claim 22 wherein the long-pass filter comprises a plurality of long-pass filter units working in combination with one another.

25. A Raman probe according to claim 24 wherein the long-pass filter comprises three or more long-pass filter units working in combination with one another.

26. A Raman probe according to claim 22 wherein the long-pass filter comprises a long-pass filter unit working in combination with a reflector unit.

27. A Raman probe according to claim 1 wherein the focusing apparatus comprises a lens disposed between the second filter and the specimen.

28. A Raman probe according to claim 1 wherein the focusing apparatus comprises a first lens for receiving light from the second filter, a vial receptacle for receiving light from the first lens, a second lens for receiving light from the vial receptacle, a third lens for receiving light from the second lens and focusing that light on a target location, and wherein the focusing apparatus is adapted so that:

(i) when the specimen is located in the vial receptacle, light is focused on the specimen; and

(ii) when the specimen is not located in the vial receptacle, light is focused at the target location.

29. A Raman probe according to claim 28 wherein the first lens, vial receptacle, second lens, third lens and target location are all aligned with one another.

30. A Raman probe according to claim 1 wherein the second filter is adapted to provide up to OD10 filtration of the laser excitation light before reflecting the Raman signal to a second optical fiber.

31. A Raman probe according to claim 1 wherein the broadband reflector is adapted to provide filtering of the laser excitation light of OD1 or more before reflecting the Raman signal to the second optical fiber.

32. A Raman probe according to claim 1 wherein the broadband reflector reflects Raman signal of>

300 cm<sup>−

1</sup>, and passes Raman signal of 0 to 300 cm<sup>−

1</sup>.

33. A Raman probe according to claim 1 wherein a normal to a surface of the broadband reflector is oriented at an angle of 45 degrees with respect to an optical path of the Raman signal between the specimen and the second filter.

34. A Raman probe according to claim 1 further comprising a lens disposed between the second filter and the second fiber.

35. A Raman probe according to claim 1 further comprising a light analyzer.

36. A Raman probe according to claim 35 wherein the light analyzer comprises a spectrometer.

37. A Raman probe according to claim 35 wherein the light analyzer comprises a spectrometer and associated analysis apparatus configured to analyze the Raman signal and to identify the specimen based on the Raman signal.

44. The Raman probe according to claim 1, wherein each of the first and second spectral filters comprises multiple layers of dielectric material.

38. A method for conducting Raman spectroscopy of a specimen, comprising:

generating laser excitation light using a light source;

passing the laser excitation light through a first spectral filter so as to block spurious signals associated with the light;

directing the laser excitation light to a second spectral filter so as to direct the laser excitation light toward the specimen;

receiving the light from the second spectral filter, focusing the light on the specimen so as to generate the Raman signal, and returning the Raman signal to the second spectral filter, wherein the second spectral filter is further configured so that when the second spectral filter receives the Raman signal from the specimen, the second spectral filter filters out unwanted laser excitation light;

passing the filtered light received from the second spectral filter to a broadband reflector configured to reflect the Raman signal to a light analyzer and to transmit laser excitation light; and

analyzing the Raman signal from the specimen to identify the specimen.

39. The method of claim 38, wherein the broadband reflector filters laser excitation light from the light received from the second filter.

40. The method of claim 39, wherein the broadband reflector provides filtering of laser excitation light of OD1 or more from the light received from the second filter.

41. The method of claim 38, wherein the broadband reflector reflects Raman signal of 300 cm⁻

1 or more, and transmits Raman signal of between 0 cm<sup>−

1</sup> and 300 cm<sup>−

1</sup>.

45. The method of claim 38, wherein each of the first and second spectral filters comprises multiple layers of dielectric material.

42. A Raman probe comprising:

a first optical fiber for receiving laser excitation light from a light source and transmitting the same;

a first filter for receiving light from the first optical fiber and adapted to pass the laser excitation light and to block spurious signals associated with the light;

a second filter for receiving laser excitation light from the first filter and adapted to direct the light toward a specimen;

focusing apparatus for receiving the laser excitation light from the second filter, focusing the light on the specimen so as to generate the Raman signal, and returning the Raman signal to the second filter, wherein the second filter is further configured so that when the second filter receives the Raman signal from the focusing apparatus, the second filter filters out laser excitation light before directing the Raman signal to a second optical fiber; and

a second optical fiber for receiving the Raman signal from the second filter and transmitting the same to a light analyzer,

wherein the focusing apparatus comprises a first lens for receiving laser excitation light from the second filter, a vial receptacle for receiving light from the first lens, a second lens for receiving light from the vial receptacle, a third lens for receiving light from the second lens and focusing that light on a target location, and wherein the focusing apparatus is adapted so that;

(i) when the specimen is located in the vial receptacle, light is focused on the specimen; and

(ii) when the specimen is not located in the vial receptacle, light is focused at the target location.

43. The Raman probe of claim 42, wherein the first lens, the vial receptacle, the second lens, the third lens, and the target location are aligned along a common optical path.