System and method for chemical sensing using trace gas detection

• US 20070115475A1
• Filed: 11/21/2006
• Published: 05/24/2007
• Est. Priority Date: 09/22/2003
• Status: Active Grant

• Current Assignee: CeLight, Inc.
• Original Assignee: CeLight, Inc.
• Inventors: Shpantzer, Isaac
• Granted Patent: US 7,426,035 B2
• Time in Patent Office: Days
• US Class Current: 356/451
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 21/171 with calorimetric detection, e.g. with thermal lens detection
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/359 using near infrared light
• CPC Class Codes: G01N 21/39 using tunable lasers

Abstract

A system and method is proposed for chemicals detection such as explosives and others, which are based on sensing of trace gases associated with the chemical. This sensing includes detection of spectrum and relative concentration of the trace gases followed by the chemical identification based on these data. The sensing is based on photothermal interferometry method modified by implementation of coherent optical detection. This modification essentially improves the device performance by increasing its sensitivity and selectivity. Improved characteristics of the device allow remote sensing of the interrogated chemicals at a distance up to 1000 meters, which is crucial for explosives detection. The coherent optical detection is performed by a coherent receiver based on 90-degrees optical hybrid.

Claims

1. A system for detecting a chemical, comprising:

a strobe configured to irradiate a first beam with a spectral energy band across at least a portion of a characteristic absorption band of a trace gas associated with the chemical;

a probe unit configured to interferometrically sense and measure the absorption of the first beam by molecules of the trace gas and determine the trace gas concentration;

wherein the trace gas is at a remote location from the strobe and the probe unit.

2. The system of claim 1, wherein the probe unit comprises

a transmitter configured to illuminate the trace gas with a second beam;

and

a coherent optical receiver.

3. The system of claim 1, wherein the chemical identification is based on the types of the trace gases detected and their concentrations.

4. The system of claim 1, wherein remote detecting is performed at distance from 1 to 1000 meters from either the strobe or the probe unit.

5. The system of claim 1, wherein the chemical is in the form of a gas, liquid or solid.

6. The system of claim 1, wherein the chemical is at an explosive site, a site of pollution and a site of a chemical weapon.

7. The optical system of claim 1, wherein the first beam consists of coherent pulses.

8. The optical system of claim 1, wherein the strobe generates the first beam having a spectrum of wavelengths in the near and middle infrared range.

9. The optical system of claim 1, wherein the strobe generates the first beam having a spectrum of wavelengths from 2.5 to 4.5 micrometers.

10. The system of claim 2, wherein

the first beam is configured to change a refractive index of the trace gas and

the second beam is configured to change a phase passing through the trace gas with the changed refractive index.

11. The system of claim 2, wherein the coherent optical receiver is configured to sense the chemical in an amount of I part per trillion or more.

12. The optical system of claim 2, wherein the transmitter generates the second beam consisting of coherent pulses.

13. The optical system of claim 2, wherein the transmitter generates the second beam having a spectrum of wavelengths in the near infrared range.

14. The optical system of claim 2, wherein the transmitter generates the second beam having a wavelength of about 1.55 micrometer.

15. The optical system of claim 2, wherein the coherent optical receiver carries out homodyne detection of the second beam.

16. The optical system of claim 2, wherein the coherent optical receiver includes an integrated 90-degrees optical hybrid.

17. The optical system of claim 2, wherein the coherent optical receiver is an integrated device.

18. The optical system of claim 2, wherein the transmitter and the coherent optical receiver are separated from each other by a distance of more than 1 meter.

19. The optical system of claim 2, wherein the coherent receiver is followed by a digital processing unit configured to determine the phase of the second beam.

20. A method for determining information about a chemical, comprising:

directing a first beam to a remote location where a trace gas associated with the chemical is present,

the first beam having one or more wavelengths that are in absorption band of a trace gas associated with the chemical, wherein the first beams interacts with the trace gas changing a refractive index of the trace gas;

directing a second beam to interact with the trace gas,

forming a third beam having a phase change relative to the second beam that corresponds with a change of a refractive index of the trace gas;

receiving at least a portion of the third beam at a receiver positioned remotely from the trace gas; and

measuring a phase shift of the third beam that is induced by the first beam and is indicative of at least one of, absorption spectrum and concentration of the trace gas.