Tunable narrowband spectrometer with acousto-optical tunable filter

• US 5,438,406 A
• Filed: 10/07/1993
• Issued: 08/01/1995
• Est. Priority Date: 10/07/1993
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Titan (L3Harris Technologies, Inc.)
• Inventors: Puschell, Jeffrey J.
• Primary Examiner(s): McGraw, Vincent P.
• Assistant Examiner(s): HANTIS, KAREN
• Application Number:
  US08/134,188
• Time in Patent Office: 663 Days
• Field of Search: 356/307-308, 356/437, 359/308, 250/339.07
• US Class Current: 356/307
• CPC Class Codes: G01J 3/1256 using acousto-optic tunable filter; acousto-optic elements or systems G02F1/11, G02F1/33

Abstract

Light from a discrete broadband visible and/or infrared light source is collimated and transmitted within an optical path that is open to an ambient environment through a spatial region of interest and is focused to a beam splitter, which splits the transmitted light into different beams and directs the different beams respectively to a pair of narrowband acousto-optical tunable filters (AOTF). One such AOTF is disposed for filtering one split transmitted light beam and is rapidly tuned through a predetermined series of different wavelengths that are characteristic of an energy absorption spectrum for a first given substance, or of a first predetermined set of given substances. The other AOTF is disposed for filtering the other split transmitted light beam and is rapidly tuned through a given substances. First and second detectors respectively detect the energy of the filtered transmitted light from the two AOTFs at each of the tuned wavelengths to provide simultaneous signals that are indicative of energy absorption spectra for the region of interest at wavelengths that are characteristic of the energy absorption spectra for the first and second given substances or for the first and second predetermined sets of given substances.

Claims

1. A tunable narrowband spectrometer comprising

a discrete broadband light source;

an optical system disposed in relation to the light source for transmitting light from the light source within an optical path through a spatial region of interest and for focusing the transmitted light on the opposite side of the region of interest from the light source;

a first narrowband acousto-optical tunable filter disposed for filtering said transmitted light;

first tuning means coupled to the first filter for tuning the first filter through a predetermined series of different wavelengths that are characteristic of an energy absorption spectrum for a first predetermined set of given substances;

a first detector disposed for detecting the energy of the transmitted light filtered by the first filter at each of said different tuned wavelengths to thereby provide a signal indicative of an energy absorption spectrum for said region of interest at wavelengths that are characteristic of said energy absorption spectrum for said first predetermined set of given substances;

wherein the first filter is disposed between the optical system and the first detector;

a second narrowband acousto-optical tunable filter disposed for filtering said transmitted light;

means disposed in relation to said optical system and the two filters for splitting the transmitted light into different light beams and for respectively directing said different light beams to the two filters;

second tuning means coupled to the second filter for tuning the second filter through a second predetermined series of different wavelengths that are characteristic of energy absorption spectra for a second predetermined different set of given substances; and

a second detector disposed for detecting the energy of said transmitted light filtered by the second filter at each of said second predetermined series of different tuned wavelengths to thereby provide a signal indicative of an energy absorption spectrum for said region of interest at wavelengths that are characteristic of said energy absorption spectra for said second predetermined set of given substances.

2. A spectrometer according to claim 1, wherein the first tuning means is adapted for also tuning the first filter to a wavelength that is uncharacteristic of said energy absorption spectrum for said first predetermined set of given substances;

and

wherein the first detector responds to the detection of energy of said transmitted light filtered by the first filter at said tuned uncharacteristic wavelength by providing a signal indicative of background energy absorption for said region of interest.

3. A spectrometer according to claim 2, wherein the second tuning means is adapted for also tuning the second filter to a second wavelength that is uncharacteristic of said energy absorption spectrum for said second predetermined set of given substances;

and

wherein the second detector responds to the detection of energy of said transmitted light filtered by the second filter at said tuned second uncharacteristic wavelength by providing a signal indicative of background energy absorption for said region of interest.

4. A tunable narrowband spectrometer, comprising

a discrete broadband light source;

an optical system disposed in relation to the light source for transmitting light from the light source within an optical path through a spatial region of interest and for focusing the transmitted light on the opposite side of the region of interest from the light source;

a first narrowband acousto-optical tunable filter disposed for filtering said transmitted light;

first tuning means coupled to the first filter for tuning the first filter through a predetermined series of different wavelengths that are characteristic of an energy absorption spectrum for a given substance;

a first detector disposed for detecting the energy of the transmitted light filtered by the first filter at each of said different tuned wavelengths to thereby provide a signal indicative of an energy absorption spectrum for said region of interest at wavelengths that are characteristic of said energy absorption spectrum for said given substance;

wherein the first filter is disposed between the optical system and the first detector;

a second narrowband acousto-optical tunable filter disposed for filtering said transmitted light;

means disposed in relation to said optical system and the two filters for splitting the transmitted light into different light beams and for respectively directing said different light beams to the two filters;

second tuning means coupled to the second filter for tuning the second filter through a second predetermined series of different wavelengths that are characteristic of an energy absorption spectra for a second given substance; and

a second detector disposed for detecting the energy of said transmitted light filtered by the second filter at each of said second predetermined series of different tuned wavelengths to thereby provide a signal indicative of an energy absorption spectrum for said region of interest at wavelengths that are characteristic of said energy absorption spectrum for said second given substance.

5. A spectrometer according to claim 4, wherein the first tuning means is adapted for also tuning the first filter to a wavelength that is uncharacteristic of said energy absorption spectrum for said first given substance;

and

wherein the first detector responds to the detection of energy of said transmitted light filtered by the first filter at said tuned uncharacteristic wavelength by providing a signal indicative of background energy absorption for said region of interest.

6. A spectrometer according to claim 5, wherein the second tuning means is adapted for also tuning the second filter to a second wavelength that is uncharacteristic of said energy absorption spectrum for said second given substance;

and

wherein the second detector responds to the detection of energy of said transmitted light filtered by the second filter at said tuned second uncharacteristic wavelength by providing a signal indicative of background energy absorption for said region of interest.