Tunable spectrometer with acousto-optical tunable filter

• US 5,444,528 A
• Filed: 07/27/1994
• Issued: 08/22/1995
• Est. Priority Date: 07/27/1994
• Status: Expired due to Fees

• Current Assignee: Titan (L3Harris Technologies, Inc.)
• Original Assignee: Titan (L3Harris Technologies, Inc.)
• Inventors: Puschell, Jeffrey J.
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US08/281,411
• Time in Patent Office: 391 Days
• Field of Search: 356/73, 356/301, 356/308, 356/319, 356/326, 356/328, 280/339.01, 280/339.02, 280/339.06, 280/339.07, 280/343, 359/308, 359/309
• US Class Current: 356/73
• CPC Class Codes: G01J 3/1256 using acousto-optic tunable filter; acousto-optic elements or systems G02F1/11, G02F1/33
• CPC Class Codes: G01J 3/44 Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry

Abstract

A tunable spectrometer includes an acousto-optical tunable filter disposed for filtering light from a discrete light source, wherein the light emerges from the filter in a simultaneous plurality of distinct beams having different orders of diffraction, with different diffraction orders having different wavelength ranges and with complementary pairs of said distinct beams having the same diffraction order respectively having substantially the same wavelength ranges. The filter is tuned to diffract light in a simultaneous plurality of distinct beams having different predetermined diffraction orders that have different wavelength ranges that include wavelengths that are characteristic of a spectrum for a given substance; and a set of a given plural number of detectors respectively detect the filtered light diffracted by the filter to thereby simultaneously provide test signals indicative of a spectrum within a spatial region of interest at wavelengths that are characteristic of the spectrum for the given substance. Another spectrometer that detects light at a wavelength that is characteristic of a Raman scattering spectrum for a given substance includes a test cell disposed within the spatial region of interest and including a plurality of mirrors disposed within the cell for reflecting the light to pass a plurality of round trips between the mirrors before emerging from the spatial region of interest to thereby enhance Raman scattering of the light by any molecules of the given substance within the cell while the light passes through the spatial region of interest.

Claims

1. A tunable spectrometer, comprising

a discrete light source;

an optical system disposed in relation to the light source for directing light from the light source through a spatial region of interest and for focusing the directed light;

an acousto-optical tunable filter disposed for filtering light from the light source, wherein the light emerges from the filter in a simultaneous plurality of distinct beams having different orders of diffraction, with different diffraction orders having different wavelength ranges and with complementary pairs of said distinct beams having the same diffraction order respectively having substantially the same wavelength ranges;

means coupled to the filter for tuning the filter to diffract light in a simultaneous plurality of distinct beams having different predetermined diffraction orders that have different wavelength ranges that include wavelengths that are characteristic of a spectrum for a given substance or of the spectra for a plurality of different given substances; and

a set of a given plural number of detectors disposed in relation to the optical system and the filter for respectively detecting the focused and filtered light diffracted by the filter in a set of said given number of said distinct beams of said different predetermined diffraction orders to thereby simultaneously provide said given number of test signals indicative of a spectrum within the spatial region of interest at wavelengths that are characteristic of said spectrum for said given substance or of the spectra for the plurality of different said given substances.

2. A spectrometer according to claim 1, wherein the filter is disposed between the light source and the spatial region of interest.

3. A spectrometer according to claim 2, further comprising

a second set of said given number of detectors disposed in relation to the optical system and the filter for respectively detecting the filtered light diffracted by the filter in a second set of said given number of said distinct beams of said different predetermined diffraction orders that are complementary to said first recited set of distinct beams to thereby provide simultaneously with the test signals reference signals indicative primarily of a spectrum of the light source at wavelengths that are characteristic of said energy absorption spectrum for said given substance or of the spectra for the plurality of different said given substances.

4. A spectrometer according to claim 1, wherein the filter is disposed between the spatial region of interest and the detectors.

5. A spectrometer according to claim 4, further comprising

means for processing the test signals to measure the concentration of said given substance within the spatial region of interest in accordance with a Raman forward scattering measurement technique.

6. A spectrometer according to claim 5, further comprising

a test cell disposed within the spatial region of interest and comprising a plurality of mirrors disposed within the cell for reflecting the light to pass a plurality of round trips between the mirrors before emerging from the spatial region of interest to thereby enhance Raman scattering of the light by any molecules of said given substance within the cell while the light passes through the spatial region of interest.

7. A tunable spectrometer, comprising

a discrete light source;

an optical system disposed in relation to the light source for directing light from the light source through a spatial region of interest and for focusing the directed light;

an acousto-optical tunable filter disposed for filtering light from the light source, wherein the light emerges from the filter in a simultaneous complementary pair of distinct beams having the same order of diffraction and substantially the same wavelength range;

means coupled to the filter for tuning the filter to diffract light in a simultaneous complementary pair of said distinct beams having a predetermined diffraction order that has a wavelength range that includes a wavelength that is characteristic of a spectrum for a given substance;

a first detector disposed in relation to the optical system and the filter for detecting the focused and filtered light diffracted by the filter in one said beam of said predetermined diffraction order to thereby provide a test signal indicative of a spectrum within the spatial region of interest at a wavelengths that is characteristic of said spectrum for said given substance; and

a second detector disposed in relation to the optical system and the filter for detecting the filtered light diffracted by the filter in the complementary other said beam of said predetermined diffraction order to thereby provide simultaneously with the test signal a reference signal indicative primarily of a spectrum of the light source at a wavelength that is characteristic of said spectrum for said given substance.

8. A spectrometer comprising

a discrete light source;

an optical system disposed in relation to the light source for directing light from the light source through a spatial region of interest and for focusing the directed light;

a detector disposed in relation to the optical system for detecting the focused light at a wavelength that is characteristic of a Raman scattering spectrum for a given substance to thereby provide a test signal indicative of a Raman scattering spectrum within the spatial region of interest at a wavelength that is characteristic of said Raman scattering spectrum for said given substance;

means for processing the test signal to measure the concentration of said given substance within the spatial region of interest in accordance with a Raman forward scattering measurement technique; and

a test cell disposed within the spatial region of interest and comprising a plurality of mirrors disposed within the cell for reflecting the light to pass a plurality of round trips between the mirrors before emerging from the spatial region of interest to thereby enhance Raman scattering of the light by any molecules of said given substance within the cell while the light passes through the spatial region of interest.

9. A spectrometer comprising

a discrete light source;

an optical system disposed in relation to the light source for directing light from the light source through a spatial region of interest and for focusing the directed light;

a detector disposed in relation to the optical system for detecting the focused light at a wavelength that is characteristic of a Raman scattering spectrum for a given substance to thereby provide a test signal indicative of a Raman scattering spectrum within the spatial region of interest at a wavelength that is characteristic of said Raman scattering spectrum for said given substance;

means for processing the test signal to measure the concentration of said given substance within the spatial region of interest in accordance with a Raman forward scattering measurement technique;

an acousto-optical tunable filter disposed between the spatial region of interest and the detector for filtering light from the spatial region of interest, wherein the light emerges from the filter in a simultaneous complementary pair of distinct beams having the same order of diffraction and substantially the same wavelength range;

means coupled to the filter for tuning the filter to diffract light in a simultaneous complementary pair of said distinct beams having a predetermined diffraction order that has a wavelength range that includes a wavelength that is characteristic of a Raman scattering spectrum for the given substance; and

a second detector disposed in relation to the optical system and the filter for detecting the filtered and focused light diffracted by the filter in one beam of said predetermined diffraction order to thereby provide simultaneously with the first recited test signal a second test signal indicative of a Raman scattering spectrum within the spatial region of interest at a wavelength that is characteristic of said Raman scattering spectrum for said given substance;

wherein the first recited detector is disposed in relation to the filter for detecting the filtered and focused light diffracted by the filter in the complementary of said beam of said predetermined diffraction order; and

wherein the processing means processes both test signals to measure the concentration of said given substance within the spatial region of interest in accordance with a Raman forward scattering measurement technique.

10. A spectrometer according to claim 9, further comprising

a test cell disposed within the spatial region of interest and comprising a plurality of mirrors disposed within the cell for reflecting the light to pass a plurality of round trips between the mirrors before emerging from the spatial region of interest to thereby enhance Raman scattering of the light by any molecules of said given substance within the cell while the light passes through the spatial region of interest.

11. A spectrometer comprising

a discrete light source;

an optical system disposed in relation to the light source for directing light from the light source through a spatial region of interest and for focusing the directed light;

a detector disposed in relation to the optical system for detecting the focused light at a wavelength that is characteristic of a Raman scattering spectrum for a given substance to thereby provide a test signal indicative of a Raman scattering spectrum within the spatial region of interest at a wavelength that is characteristic of said Raman scattering spectrum for said given substance;

means for processing the test signal to measure the concentration of said given substance within the spatial region of interest in accordance with a Raman forward scattering measurement technique;

a narrowband acousto-optical tunable filter disposed between the light source and the spatial region of interest for filtering said light provided by the light source; and

means coupled to the first filter for tuning the first filter to a predetermined wavelength.

12. A spectrometer according to claim 11, further comprising

a test cell disposed within the spatial region of interest and comprising a plurality of mirrors disposed within the cell for reflecting the filtered light to pass a plurality of round trips between the mirrors before emerging from the spatial region of interest to thereby enhance Raman scattering of the light by any molecules of said given substance within the cell while the light passes through the spatial region of interest.

13. A spectrometer according to claim 11, further comprising

a second acousto-optical tunable filter disposed between the spatial region of interest and the detector for filtering light from the spatial region of interest, wherein the light emerges from the second filter in a simultaneous-complementary pair of distinct beams having the same order of diffraction and substantially the same wavelength range;

means coupled to the second filter for tuning the second filter to diffract light in a simultaneous complementary pair of said distinct beams having a predetermined diffraction order that has a wavelength range that includes a wavelength that is characteristic of a Raman scattering spectrum for the given substance; and

a second detector disposed in relation to the optical system and the second filter for detecting the filtered and focused light diffracted by the second filter in one beam of said predetermined diffraction order to thereby provide simultaneously with the first recited test signal a second test signal indicative of a Raman scattering spectrum within the spatial region of interest at a wavelength that is characteristic of said Raman scattering spectrum for said given substance;

wherein the first recited detector is disposed in relation to the filter for detecting the filtered and focused light diffracted by the second filter in the complementary of said beam of said predetermined diffraction order; and

wherein the processing means processes both test signals to measure the concentration of said given substance within the spatial region of interest in accordance with a Raman forward scattering measurement technique.

14. A spectrometer according to claim 13, further comprising

a test cell disposed within the spatial region of interest and comprising a plurality of mirrors disposed within the cell for reflecting the filtered light from the first filter to pass a plurality of round trips between the mirrors before emerging from the spatial region of interest to thereby enhance Raman scattering of the light by any molecules of said given substance within the cell while the light passes through the spatial region of interest.

15. A spectrometer comprising

a discrete light source;

an optical system disposed in relation to the light source for directing light from the light source through a spatial region of interest and for focusing the directed light;

a detector disposed in relation to the optical system for detecting the focused light at a wavelength that is characteristic of a Raman scattering spectrum for a given substance to thereby provide a test signal indicative of a Raman scattering spectrum within the spatial region of interest at a wavelength that is characteristic of said Raman scattering spectrum for said given substance;

means for processing the test signal to measure the concentration of said given substance within the spatial region of interest in accordance with a Raman forward scattering measurement technique;

a second discrete light source;

a second optical system disposed in relation to the second light source and the spatial region of interest for directing light from the second light source through the spatial region of interest and for focusing the directed light from the second light source;

an acousto-optical tunable filter disposed for filtering light from the second light source;

means coupled to the filter for tuning the filter to provide the filtered light at a tuned wavelength that is characteristic of an energy absorption spectrum for said given substance;

a second detector disposed in relation to the optical system for detecting the focused and filtered light from the second light source at said tuned wavelength to thereby provide a second test signal indicative of an energy absorption spectrum for said spatial region of interest at a wavelength that is characteristic of said energy absorption spectrum for said given substance; and

means for processing the second test signal to measure the concentration of said given substance within the spatial region of interest in accordance with an energy absorption spectrum measurement technique.