Differential absorption lidar

Patent metadata

Field	Value
Publication number	US-10458904-B2
Application number	US-201615279177-A
Country	US
Kind code	B2
Filing date	Sep 28, 2016
Priority date	Sep 28, 2015
Publication date	Oct 29, 2019
Grant date	Oct 29, 2019

Abstract

A system for remotely detecting gas concentration is provided. The system includes a plurality of light sources. At least a first one of the light sources generates light having a first wavelength and a first polarization, and at least a second one of the light sources generates light having a second, different wavelength and a second polarization that is orthogonal to the first polarization. The light from the light sources is placed on a common transmission path, and is directed to a target area by a steering mirror. Light reflected from the target area is received and directed to a detector. The detector provides information regarding the time of arrival and amplitude of the received light, allowing range and gas concentration information to be obtained. In some embodiments the detector is an imaging detector, allowing three-dimensional range information to be obtained from the target area from a single light pulse.

First claim

What is claimed is:

1. A sensor system, comprising:
a first light source assembly, wherein the first light source assembly is operable to output light at a first wavelength;
a second light source assembly, wherein the second light source assembly is operable to output light at a second wavelength, wherein the first wavelength is different than the second wavelength;
a combiner, wherein the light output from the first light source assembly and the light output from the second light source assembly are directed along a common path;
and
transmit optics, wherein the first light source assembly includes a first laser, wherein the first light source assembly further includes a first volume Bragg grating (VBG), wherein the first VBG receives light from the first laser and outputs light at the first wavelength, wherein the second light source assembly includes a second laser, wherein the second light source assembly further includes a second VBG, and wherein the second VBG receives light from the second laser and outputs light at the second wavelength.

2. The sensor system of claim 1 , wherein the common path includes an optical fiber.

3. The sensor system of claim 1 , further comprising:
a quarter waveplate, wherein the quarter waveplate receives the light directed along the common path, wherein the light output by the first light source assembly has a first polarization, wherein the light output by the second light source assembly has a second polarization that is orthogonal to the first polarization, wherein the combiner is a polarization combiner, and wherein the transmit optics receive light circularly polarized by the quarter waveplate.

4. The sensor system of claim 3 , wherein the light output by the first VBG has a first linear polarization, and wherein the light output by the second VBG has a second linear polarization.

5. The sensor system of claim 4 , wherein the light output by the first VBG has a first line width, and wherein the light output by the second VBG has a second line width.

6. The sensor system of claim 4 , further comprising:
a pick off mirror; and
a laser monitor, wherein the pick off mirror is between the quarter waveplate and the transmit optics, wherein the pick off mirror directs a portion of the light circularly polarized by the quarter waveplate to the laser monitor, and wherein the laser monitor detects a wavelength and energy content of the circularly polarized light.

7. The sensor system of claim 6 , wherein the laser monitor includes:
a beam splitter, wherein the beam splitter receives light from the pick off mirror and divides the received light into first and second beams;
a gas cell, wherein the gas cell receives light included in the first beam;
a first integrating sphere, wherein the first integrating sphere receives the light included in the first beam that has passed through the gas cell;
a first detector, wherein the first detector receives light from the first integrating sphere;
a second integrating sphere, wherein the second integrating sphere receives the light included in the second beam; and
a second detector, wherein the second detector receives light from the second integrating sphere.

8. A sensor system, comprising:
a first light source assembly including a first laser, wherein the first light source assembly is operable to output light at a first wavelength;
a second light source assembly including a second laser, wherein the second light source assembly is operable to output light at a second wavelength, and wherein the first wavelength is different than the second wavelength;
a combiner, wherein the light output from the first light source assembly and the light output from the second light source assembly are directed along a common path; and
transmit optics, wherein the transmit optics include a steering mirror.

9. The sensor system of claim 8 , further comprising:
a quarter waveplate, wherein the quarter waveplate receives the light directed along the common path, wherein the light output by the first light source assembly has a first polarization, wherein the light output by the second light source assembly has a second polarization that is orthogonal to the first polarization, wherein the combiner is a polarization combiner, wherein the transmit optics receives light circularly polarized by the quarter waveplate, and wherein the steering mirror directs the light circularly polarized by the quarter waveplate towards a target area.

10. The sensor system of claim 9 , further comprising:
a receive telescope; and
a detector, wherein light reflected from the target area is received at the receive telescope and passed to the detector.

11. The sensor system of claim 10 , wherein the detector is a single pixel detector.

12. The sensor system of claim 10 , wherein the detector includes an array of pixels.

13. The sensor system of claim 10 , further comprising a processor, wherein the processor determines a time of flight of light output from at least one of the lasers and received at the detector, and wherein the processor receives a signal from the detector regarding an amplitude of the light received at the detector.

14. The sensor system of claim 7 , wherein the transmit optics further include:
a multiple mode fiber;
a collimator; and
a diffuser, wherein the fiber receives the light circularly polarized by the quarter waveplate, wherein the collimator receives light from the fiber, wherein the diffuser receives light from the collimator, and wherein a steering mirror receives light from the diffuser.

15. A method for remotely measuring a gas concentration, comprising:
producing light having a first wavelength;
producing light having a second wavelength;
directing the light having a first wavelength and the light having a second wavelength along a common path;
directing the light having the first wavelength to a target area, wherein the light having the first wavelength is produced at a first point in time;
directing the light having the second wavelength to the target area, wherein the light having the second wavelength is produced at a second point in time;
receiving first reflected light at a detector, wherein the first reflected light includes light having the first wavelength;
determining a time of arrival and an amplitude of the light having the first wavelength;
receiving second reflected light at the detector, wherein the second reflected light includes light having the second wavelength;
determining a time of arrival and an amplitude of the light having the second wavelength;
determining a range to the target area from at least one of:
a difference between a time of transmission and the time of arrival of the light having the first wavelength; and
a difference between a time of transmission and the time of arrival of the light having the second wavelength; and
determining a concentration of a gas of interest from a difference between the amplitude of the light having a first wavelength and the amplitude of the light having a second wavelength.

16. The sensor system of claim 8 , wherein the common path includes an optical fiber.

17. The method of claim 15 , wherein the first point in time is within about 2 microsecond or less of the second point in time.

18. The method of claim 15 , wherein the detector is an imaging detector, and wherein the method further includes:
combining three-dimensional image data from the detector with two-dimensional image data from a context camera; and
displaying the combined image data.

19. The met

Assignees

• Ball Aerospace & Tech Corp

Inventors

• Bartholomew Jarett Levi

Classifications

• G01N21/3151 Primary

  using two sources of radiation of different wavelengths (G01N21/33 - G01N21/39 take precedence) · CPC title

• G01S17/894

  Three-dimensional [3D] imaging with simultaneous measurement of time-of-flight at a two-dimensional [2D] array of receiver pixels, e.g. time-of-flight cameras or flash lidar · CPC title

• G01S17/86

  Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders · CPC title

• G01S7/499

  using polarisation effects · CPC title

• G01S7/497

  Means for monitoring or calibrating · CPC title