Method and Apparatus for Improvement of Spectrometer Stability, and Multivariate Calibration Transfer

• US 20080117405A1
• Filed: 11/16/2006
• Published: 05/22/2008
• Est. Priority Date: 11/16/2006
• Status: Active Grant

• Current Assignee: Rockley Photonics Limited
• Original Assignee: TruTouch Technologies, Inc.
• Inventors: ver Steeg, Ben, Maynard, John D., Haass, Michael, Benz, Zachary, Ridder, Trent
• Granted Patent: US 7,889,349 B2
• Time in Patent Office: Days
• US Class Current: 356/4.01
• CPC Class Codes: G01J 3/45 Interferometric spectrometry

Abstract

The present invention provides improved methods and apparatuses for accurate measurements using interferometers. A functional relationship between the optical path difference and time is determined from a reference signal from an interferometer. The times at which the interferometer had specific optical path differences can be determined from the functional relationship. Those times can then be used to select times at which the spectroscopic signal from the interferometer was produced at the specific optical path differences. The invention can be applied, as examples, to maintain instrument calibration, and to transfer or compare calibrations or measurements across different interferometers.

Claims

1. A method of producing an interferogram from a reference signal and a spectroscopic signal, comprising:

a. Determining from a reference signal a functional relationship between optical path difference and time;

b. Determining from the functional relationship one or more times that correspond to a predetermined set of optical path differences;

c. Determining the value of the spectroscopic signal at the determined times to produce the interferogram.

2. A method as in claim 1, wherein step a. comprises determining from discrete measurements of the reference signal a functional relationship between optical path difference and time.

3. A method as in claim 1, wherein determining a functional relationship comprises determining optical path difference as a function of time, where the function is continuous over the range of optical path differences in the predetermined set.

4. A method as in claim 3, wherein the functional relationship is determined using at least one of a spline, polynomial, since Savitzky-Golay or combination thereof.

5. A method as in claim 1, wherein the optical path differences in the predetermined set have consistent spacing between optical path differences.

6. A method of producing interferograms on a plurality of interferometric systems, comprising, on each interferometric system,

a. Acquiring a reference signal and a spectroscopic signal;

b. Determining an interferogram using the method of claim 1, with the predetermined set of optical path differences the same for the application of claim 1 to each interferometric system.

7. A method as in claim 1, wherein the predetermined set of optical path differences contains at least one optical path difference that does not correspond to a zero crossing of the reference signal.

10. A method of determining an interferogram using a spectroscopic instrument, comprising

a. Determining a reference signal by:

i. Providing an effectively monochromatic light source,

ii. Modulating light from the effectively monochromatic light source using an interferometric system;

iii. Detecting the output of the interferometric system as an analog signal using a reference photodetector;

iv. Converting the analog signal to a digital reference signal;

b. Determining a spectroscopic signal by;

i. Providing a light source;

ii. Modulating light from the light source using the interferometric system;

iii. Providing a sample such that light from the interferometric system interacts with the sample;

iv. Detecting the output of the interferometric system as an analog signal using a spectroscopic photodetector;

v. Converting the analog signal to a digital spectroscopic signal;

c. Determining an interferogram using the method of claim 1.

11. A method as in claim 10, wherein the reference photodetector and the spectroscopic photodetector comprise a single photodetector apparatus.

12. A method as in claim 10, wherein the interferometric system comprises a single interferometer.

13. A method as in claim 10, wherein the interferometric system comprises a plurality of interferometers having at least one common optical component.

14. A method of determining an interferogram using a spectroscopic instrument, comprising

a. Determining a reference signal by:

i. Providing an effectively monochromatic light source;

ii. Modulating light from the effectively monochromatic light source using an interferometric system;

iii. Detecting the output of the interferometric system as an analog signal using a reference photodetector;

iv. Converting the analog signal to a digital reference signal;

b. Determining a spectroscopic signal by;

i. Providing a light source;

ii. Providing a sample such that light from the light source interacts with the sample;

iii. Modulating tight after interaction with the sample using the interferometric system;

iv. Detecting the output of the interferometric system as an analog signal using a spectroscopic photodetector;

v. Converting the analog signal to a digital spectroscopic signal;

c. Determining an interferogram using the method of Claim 1.

15. A method as in claim 14, wherein the reference photodetector and the spectroscopic photodetector comprise a single photodetector apparatus.

16. A method as in claim 14, wherein the interferometric system comprises a single interferometer.

17. A method as in claim 14, wherein the interferometric system comprises a plurality of interferometers having at least one common optical component.

18. A method as in claim 10, wherein the spectroscopic light interacts with the sample due to at least one of atomic or molecular absorption, atomic or molecular emission, Raman scattering, fluorescence, phosphorescence.

19. A method as in claim 14, wherein the spectroscopic light interacts with the sample due to at least one of atomic or molecular absorption, atomic or molecular emission, Raman scattering, fluorescence, phosphorescence.

20. A method as in claim 10, wherein the sample is the light source.

21. A method as in claim 14, wherein the sample is the light source.

22. A method as in claim 1 wherein the reference signal is generated at least in part using electronic circuit components, wherein the method further comprises compensating the reference signal for frequency distortions caused by the electronic circuit components.

23. A method as in claim 22, wherein the compensation is a uniform time delay for a plurality of frequencies in the reference signal.

24. The method as in claim 22 wherein the compensation is achieved using a digital filter whose frequency response is substantially the inverse of the response distortions in the reference signal.

25. The method as in claim 22 wherein the compensation is achieved using a combination of (a) a uniform time delay for a plurality of frequencies in the reference signal and (b) a digital filter whose frequency response is substantially the inverse of the response distortions in the reference signal.

26. A method as in claim 1, wherein the spectroscopic signal is generated at least in part using electronic circuit components, wherein the method further comprises compensating the spectroscopic signal for frequency distortions caused by the electronic circuit components.

27. A method as in claim 26, wherein the compensation is a uniform time delay for a plurality of frequencies in the spectroscopic signal.

28. The method as in claim 26 wherein the compensation is achieved using a digital filter whose frequency response is substantially the inverse of the response distortions in the spectroscopic signal.

29. The method as in claim 26 wherein the compensation is achieved using a combination of (a) a uniform time delay for a plurality of frequencies in the spectroscopic signal and (b) a digital filter whose frequency response is substantially the inverse of the response distortions in the spectroscopic signal.

30. A spectroscopic apparatus, comprising:

a. A interferometric system, adapted to produce a digitized reference signal and a spectroscopic signal, wherein the reference signal comprises reference values each paired with a corresponding measurement time; and

adapted to produce a digitized spectroscopic signal, wherein the spectroscopic signal comprises spectroscopic values each paired with a corresponding measurement time;

b. A processing system, adapted to produce an interferogram according to the method of claim 1.

31. A method of determining a property of a sample using a second interferometric system and a model relating the property to an interferogram determined on a first interferometric system, comprising, on the second interferometric system:

a. Acquiring a reference signal and a spectroscopic signal;

b. Determining an interferogram using the method of claim 1, with the predetermined set of optical path differences the same for the application of claim 1 as the set of optical path differences used in generating an interferogram from the first interferometric system used in generating the model.

8. A method of generating an interferogram from a second interferometric instrument, comprising:

a. Determining a spectroscopic signal and a reference signal using the second interferometric instrument;

b. Determining a set of optical path differences at which an interferogram was generated using a first interferometric instrument;

c. Determining from the reference signal of the second interferometric instrument a functional relationship between optical path difference and time;

d. Determining from the functional relationship one or more times that correspond to optical path differences in the set of optical path differences determined in step a;

e. Determining the value of the spectroscopic signal of the second interferometric instrument at the determined times to produce the interferogram.

9. A method as in claim 8, wherein at least one of (a) the optical wavelength of the reference signal or (b) the modulated frequency of the optical wavelength of the reference signal on the first interferometric instrument is not identical to the corresponding parameter on the second interferometric instrument

32. A method of determining a property of a sample using a second interferometric system, comprising

a. determining a model relating a sample property to one or more interferograms, spectra obtained from one or more interferograms, or a combination thereof, wherein the interferograms are determined on a first interferometric system;

b. determining one or more interferogram from a sample on the second interferometric system according to claim 8;

c. determining the property from the model and the one or more interferograms determined in b.

33. A method as in claim 32, wherein the reference signal on the second interferometric system is generated at least in part using electronic circuit components, wherein the method further comprises compensating the reference signal for frequency distortions caused by the electronic circuit components.

34. A method as in claim 33, wherein the compensation is a uniform time delay for a plurality of frequencies in the reference signal.

35. The method as in claim 33 wherein the compensation is achieved using a digital filter whose frequency response is substantially the inverse of the response distortions in the reference signal.

36. The method as in claim 33 wherein the compensation is achieved using a combination of (a) a uniform time delay for a plurality of frequencies in the reference signal and (b) a digital filter whose frequency response is substantially the inverse of the response distortions in the reference signal.

37. A method as in claim 32, wherein the spectroscopic signal in the second interferometric system is generated at least in part using electronic circuit components, wherein the method further comprises compensating the spectroscopic signal for frequency distortions caused by the electronic circuit components.

38. A method as in claim 37, wherein the compensation is a uniform time delay for a plurality of frequencies in the spectroscopic signal.

39. The method as in claim 37 wherein the compensation is achieved using a digital filter whose frequency response is substantially the inverse of the response distortions in the spectroscopic signal.

40. The method as in claim 37 wherein the compensation is achieved using a combination of (a) a uniform time delay for a plurality of frequencies in the spectroscopic signal and (b) a digital filter whose frequency response is substantially the inverse of the response distortions in the spectroscopic signal.