Multiple wavelength cavity ring down gas sensor

• US 8,437,000 B2
• Filed: 06/29/2010
• Issued: 05/07/2013
• Est. Priority Date: 06/29/2010
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Cole, Barrett E., Marta, Terry, Cox, James Allen, Nusseibeh, Fouad
• Primary Examiner(s): Lauchman, L. G.
• Assistant Examiner(s): Valentin, II, Juan D
• Application Number:
  US12/825,985
• Publication Number:
  US 20110317164A1
• Time in Patent Office: 1,043 Days
• Field of Search: None
• US Class Current: 356/437
• CPC Class Codes: G01N 21/031 Multipass arrangements
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/39 using tunable lasers

Abstract

An illustrative cavity ring down gas sensor includes an optical cavity for receiving a gas to be detected and at least two electromagnetic radiation sources. The first electromagnetic radiation source may emit a first beam of light having a wavelength corresponding to an absorption wavelength of the gas to be detected, and the second electromagnetic radiation source may emit a second beam of light having a second wavelength that is off of an absorption wavelength of the gas to be detected. The first beam of light may detect a cavity ring down time decay, which is related to the concentration of the gas to be detected. The second beam of light may be used to detect a baseline cavity ring down time decay, which may be used to help increase the accuracy of the sensor by, for example, helping to compensate the concentration of the gas detected by the first beam of light for sensor variations caused by, for example, sensor age, temperature or pressure changes, and/or other conditions.

Claims

1. A gas sensor for detecting a gas of interest, the gas of interest having one or more absorption lines, the gas sensor comprising:

an optical cavity for receiving the gas of interest, the optical cavity defined by one or more optical segments separating at least two minors;

a first electromagnetic radiation source configured to emit a first beam of light having a first wavelength, wherein the first wavelength corresponds to one of the one or more absorption lines of the gas of interest;

a second electromagnetic radiation source configured to emit a second beam of light having a second wavelength, wherein the second wavelength does not correspond to any of the one or more absorption lines of the gas of interest;

wherein the at least two mirrors are configured to reflect the first beam of light and the second beam of light through the one or more optical segments of the optical cavity and the gas of interest; and

a first detector configured to detect a cavity ring down time decay of the first beam of light corresponding to an absorption of the first beam of light by the gas in the optical cavity;

wherein at least one of the at least two mirrors is actuatable to move the optical cavity in and out of one or more node positions that provide one or more resonance conditions in the optical cavity; and

wherein at least one of the at least two mirrors that is actuatable is electrically deformable, wherein the electrically deformable minor deforms around the one or more node positions according to an applied electrical potential.

2. The gas sensor of claim 1, wherein the first detector is also configured to detect a cavity ring down time decay of the second beam of light in the optical cavity, indicating a baseline cavity ring down time.

3. The gas sensor of claim 1, further comprising a second detector configured to detect a cavity ring down time decay of the second beam of light in the optical cavity, indicating a baseline cavity ring down time.

4. The gas sensor of claim 1 wherein the electrically deformable mirror is a piezoelectric mirror.

5. The gas sensor of claim 1 further comprising an optical element that directs both the first beam of light and the second beam of light into the optical cavity.

6. The gas sensor of claim 1 wherein a first mirror of the at least two mirrors is an entrance mirror configured to couple both at least a portion of the first beam of light from the first electromagnetic radiation source and at least a portion of the second beam of light from the second electromagnetic radiation source into the optical cavity.

7. The gas sensor of claim 1 wherein a first mirror of the at least two mirrors is a first entrance mirror configured to couple at least a portion of the first beam of light from the first electromagnetic radiation source into the optical cavity, and a second mirror of the at least two mirrors is a second entrance mirror configured to couple at least a portion of the second beam of light from the second electromagnetic radiation source into the optical cavity.

8. The gas sensor of claim 1 wherein the first beam of light and the second beam of light are sequentially coupled into the optical cavity.

9. A gas sensor comprising:

a first laser configured to emit a first beam of light having a first wavelength that corresponds to an absorption wavelength of a gas to be detected;

a second laser configured to emit a second beam of light having a second wavelength that is different than the first wavelength;

an optical cavity including at least two mirrors separated by one or more optical segments, wherein the at least two mirrors couple the first beam of light from the first laser and the second beam of light from the second laser into the optical cavity, wherein at least one of the at least two mirrors is electrically tunable to move the optical cavity in and out of two or more resonance conditions, wherein a first resonance condition corresponds to the first wavelength, and a second resonance condition corresponds to the second wavelength, and wherein the one or more of the at least two mirrors that is electrically tunable is configured to deform the mirror around at least one node position according to an applied electrical signal; and

one or more optical detectors for detecting a first cavity ring down time decay of the first beam of light in the optical cavity, and a second cavity ring down time decay of the second beam of light in the optical cavity.

10. The gas sensor of claim 9 wherein the first beam of light and the second beam of light are sequentially coupled into the optical cavity according to the position of the at least one tunable mirror.

11. The gas sensor of claim 9 wherein the first beam of light is coupled into the optical cavity via a first mirror and the second beam of light is coupled into the optical cavity via a second mirror.

12. The gas sensor of claim 9 wherein the first beam of light and the second beam of light are coupled into the optical cavity via a common optical element.

13. A method of detecting a gas, the method comprising:

providing an optical cavity including at least two mirrors separated by one or more optical segments, wherein the optical cavity is configured to receive a gas;

coupling a first light beam having a first wavelength from a first electromagnetic radiation source into the optical cavity, wherein the first wavelength corresponds to an absorption wavelength of the gas in the optical cavity;

electrically deforming at least one of the at least two mirrors to move the optical cavity into a resonance condition at the first wavelength;

detecting a first cavity ring down time decay of the first beam of light in the optical cavity;

coupling a second light beam having a second wavelength from a second electromagnetic radiation source into the optical cavity, wherein the second wavelength corresponds to a wavelength that has relatively little or no absorption by the gas in the optical cavity;

electrically deforming at least one of the at least two mirrors to move the optical cavity into a resonance condition at the second wavelength; and

detecting a second cavity ring down time decay of the second beam of light in the optical cavity, indicating a baseline cavity ring down time.

14. The method of claim 13, wherein the first light beam is coupled into the optical cavity by tuning a first mirror of the optical cavity to a first node position.

15. The method of claim 14, wherein the second light beam is coupled into the optical cavity by tuning the first mirror of the optical cavity to a second node position.

16. The method of claim 13, wherein a first mirror of the at least two mirrors is an entrance mirror for the first beam of light and the second beam of light.

17. The method of claim 13, wherein a first mirror of the at least two mirrors is an entrance mirror for the first beam of light and a second mirror of the at least two mirrors is an entrance mirror for the second beam of light.