Method and apparatus for optical spectroscopy incorporating a vertical cavity surface emitting laser (VCSEL) as an interferometer reference

• US 6,654,125 B2
• Filed: 04/04/2002
• Issued: 11/25/2003
• Est. Priority Date: 04/04/2002
• Status: Expired due to Fees

• Current Assignee: Inlight Solutions, Inc.
• Original Assignee: Inlight Solutions, Inc.
• Inventors: Maynard, John D., Ridder, Trent
• Primary Examiner(s): Turner, Samuel A.
• Assistant Examiner(s): Connolly, Patrick
• Application Number:
  US10/116,267
• Publication Number:
  US 20030189709A1
• Time in Patent Office: 600 Days
• Field of Search: 356/451, 250/339.07, 250/339.08, 250/339.09
• US Class Current: 356/451
• CPC Class Codes: G01J 3/453 by correlation of the amplitudes

Abstract

A vertical cavity surface-emitting laser (VCSEL) package utilized as a laser reference for use in interferometry. The primary disadvantage of VCSELs, in terms of interferometry, has been found to be the relatively poor wavenumber stability of the beam. The present invention is a method and apparatus that makes viable a VCSEL package suitable for use as a reference in interferometry. The VCSEL package incorporates current control, temperature control and an algorithm for correcting wavenumber drift. The algorithm is derived from spectroscopic analysis of a reference sample having a known spectrum and comparing the generated spectrum to the known spectrum.

Claims

1. A subassembly for use in optical spectroscopy comprising:

an interferometer including optical components for receiving light and passing the light along a defined light path, the optical components including a beamsplitter separating the light into two portions and means for introducing a path length difference between the portions;

a vertical cavity surface emitting laser, including electronics to drive the vertical cavity surface emitting laser to project a beam therefrom, operatively mounted on the interferometer with the beam generally following the defined light path to act as a reference laser for the interferometer, to a photodetector, the vertical cavity surface emitting laser including means for temperature control and means for current control connected thereto and computing means including an algorithm for correcting wavenumber drift by the vertical cavity surface emitting laser.

2. The subassembly of claim 1, wherein the algorithm for correcting wavenumber drift by the vertical cavity surface emitting laser includes factors derived from spectroscopic analysis of a reference sample utilizing the interferometer and vertical cavity surface emitting laser and comparing at least a portion of the generated spectrum to a known spectrum for the reference sample.

3. The subassembly of claim 2, wherein the algorithm employs the relative difference between at least a portion of the generated spectrum and the known spectrum of the reference sample.

4. The subassembly of claim 1, wherein the algorithm for correcting wavenumber drift by the vertical cavity surface emitting laser includes factors derived from multiple spectroscopic analysis of a reference sample utilizing a second interferometer and a second vertical cavity surface emitting laser of the same type and comparing at least a portion of each of the generated spectrum to a know spectrum for the reference sample.

5. The subassembly of claim 1, wherein the interferometer is a Fourier transform type interferometer.

6. The subassembly of claim 2, wherein the reference sample includes at least one rare-earth oxide.

7. The subassembly of claim 6, wherein the at least one rare-earth oxide is doped into a diffusely reflective substrate.

8. The subassembly of claim 6, wherein the at least one rare-earth oxide is doped into a transmissive substrate.

9. The subassembly of claim 6, wherein the at least one rare-earth oxide is selected from the group consisting of:

erbium oxide, dysprosium oxide, holmium oxide or samarium oxide.

10. The subassembly of claim 2, wherein the reference sample is a rare gas emission lamp selected from the group consisting of:

a neon emission lamp, a krypton emission lamp, an argon emission lamp or a xenon emission lamp.

11. The subassembly of claim 2, wherein the reference sample is one or more etalons that may be measured simultaneously or in series.

12. The subassembly of claim 1, wherein the subassembly is mounted in a spectrometer system including a sample holder and the reference sample is measured while positioned in the sample holder.

13. In an optical spectrometry system including an interferometer which introduces an optical pathlength difference to portions of a beam along defined optical paths, the interferometer including means for mounting a reference laser so that a beam generated by the reference laser is received generally along the same defined optical paths and received by a photodetector to elucidate path length differences and provide an internal wavenumber axis standard for measurements on the optical spectrometry system, the improvement comprising:

a vertical cavity surface emitting laser disposed on the means for mounting a reference laser, the vertical cavity surface emitting laser including means for temperature control and means for current control connected thereto and computing means including an algorithm for correcting wavenumber drift by the vertical cavity surface emitting laser.

14. The optical spectrometry system of claim 13, wherein the algorithm for correcting wavenumber drift by the vertical cavity surface emitting laser includes factors derived from spectroscopic analysis of a reference sample utilizing the interferometer and vertical cavity surface emitting laser and comparing at least a portion of the generated spectrum to a known spectrum for the reference sample.

15. The optical spectrometry system of claim 14, wherein the algorithm employs the relative difference between at least a portion of the generated spectrum and the known spectrum of the reference sample.

16. The optical spectrometry system of claim 13, wherein the algorithm for correcting wavenumber drift by the vertical cavity surface emitting laser includes factors derived from multiple spectroscopic analysis of a reference sample utilizing a second interferometer and a second vertical cavity surface emitting laser of the same type and comparing at least a portion of each of the generated spectrum to a know spectrum for the reference sample.

17. The optical spectrometry system of claim 13, wherein the interferometer is a Fourier transform type interferometer.

18. The optical spectrometry system of claim 14, wherein the reference sample includes at least one rare-earth oxide.

19. The optical spectrometry system of claim 18, wherein the at least one rare-earth oxide is doped into a diffusely reflective substrate.

20. The optical spectrometry system of claim 18, wherein the at least one rare-earth oxide is doped into a transmissive substrate.

21. The optical spectrometry system of claim 18, wherein the at least one rare-earth oxide is selected from the group consisting of:

erbium oxide, dysprosium oxide, holmium oxide or samarium oxide.

22. The optical spectrometry system of claim 14, wherein the reference sample is a rare gas emission lamp selected from the group consisting of:

a neon emission lamp, a krypton emission lamp, an argon emission lamp or a xenon emission lamp.

23. The optical spectrometry system of claim 14, wherein the reference sample is one or more etalons that may be measured simultaneously or in series.

24. The optical spectrometry system of claim 13, further comprising a sample holder, wherein the reference sample is measured while positioned in the sample holder.

25. A method for correction of a vertical cavity surface emitting laser used as a reference laser in an optical spectrometry system, the method comprising the steps of:

providing an interferometer including optical components for receiving light and passing the light along a defined light path and providing a vertical cavity surface emitting laser projecting a beam therefrom operatively mounted on the interferometer with the beam generally following the defined light path to act as a reference laser for the interferometer; and

correcting the wavenumber drift by the vertical cavity surface emitting laser by providing computing means including an algorithm derived from spectrometric analysis of a reference utilizing the vertical cavity surface emitting laser as a reference laser and comparing at least a portion of the spectrum generated to at least a portion of a known spectrum for the reference sample.

26. The method of claim 25, wherein the algorithm for correcting wavenumber drift by the vertical cavity surface emitting laser is derived by spectroscopic analysis of a reference sample utilizing the interferometer and vertical cavity surface emitting laser and comparing at least a portion of the generated spectrum to a known spectrum for the reference sample.

27. The method of claim 26, wherein the algorithm employs the relative difference between at least a portion of the generated spectrum and the known spectrum of the reference sample.

28. The method of claim 26, wherein the algorithm employs a derivative based determination of wavenumber locations of spectral features.

29. The method of claim 26, wherein the algorithm employs a center of gravity based determination of wavenumber location of spectral features.

30. The method of claim 26, wherein the algorithm employs an interpolation based determination of wavenumber location of spectral properties.

31. The method of claim 26, wherein the algorithm employs a wavenumber shift versus wavenumber regression to determine the shift correction.

32. The method of claim 25, wherein the algorithm for correcting wavenumber drift by the vertical cavity surface emitting laser is derived from multiple spectroscopic analysis of a reference sample utilizing a second interferometer and a second vertical cavity surface emitting laser of the same type and comparing at least a portion of each of the generated spectrum to a know spectrum for the reference sample.