System for monitoring contamination of optical elements in a Raman gas analyzer

• US 5,929,981 A
• Filed: 06/18/1996
• Issued: 07/27/1999
• Est. Priority Date: 06/18/1996
• Status: Expired due to Term

• Current Assignee: Datex-Ohmeda Incorporated (GE Healthcare Technologies, Inc.)
• Original Assignee: Ohmeda, Inc. (Linde Plc)
• Inventors: Keilbach, Kevin A.
• Primary Examiner(s): HANTIS, KAREN
• Application Number:
  US08/665,387
• Time in Patent Office: 1,134 Days
• Field of Search: 356/445-448, 356/335-339, 356/73, 356/300, 356/432-444, 356/340-343, 356/246, 356/318, 356/301, 356/319, 356/418, 356/237.1-237.6, 372/107-109, 372/75, 372/69, 250/574, 250/573, 250/575-577, 250/338.5, 250/339.01-339.09
• US Class Current: 356/73
• CPC Class Codes: G01N 21/15 Preventing contamination of the components of the optical system or obstruction of the light path
• CPC Class Codes: G01N 21/65 Raman scattering

Abstract

A photodetector is used to monitor contamination of optical elements within an optical system. The photodetector is aligned to detect nonspecular/diffuse reflections attributable to surface irregularities of particulate matter residing on the surfaces of the optical elements within the system. An increase in the intensity of the nonspecular reflections corresponds to increased levels of contamination on the surface of the optical element. An electronic detector circuit performs signal processing on the photodetector output signal and generates an output signal corresponding to the contamination level. In another aspect of the invention, the photodetector circuit is incorporated into a Raman gas analysis system. The invention also provides a method for detecting nonspecular reflection in an optical resonant system by generating and resonating an optical energy beam in an optical resonant cavity so as to irradiate an optical element within the cavity; detecting optical energy reflecting off the optical element; and generating an output signal functionally related to the intensity of the detected optical energy.

Claims

1. A system for detecting contamination on a surface of an optical element in an optical system comprising:

a laser having a resonant cavity, wherein said laser is disposed to generate a beam of optical radiation for transmission in the optical system and irradiation of the optical element, wherein the optical element is located within said laser resonant cavity;

a contamination detector positioned to detect nonspecular optical energy scattered from the surface of the optical element;

a contamination detector circuit operably coupled to said contamination detector to receive signals from said contamination detector which are representative of an intensity of the nonspecular optical energy scattered from the surface of the optical element detected by said contamination detector, said contamination detector circuit having an output which produces an electronic signal which is representative of the intensity of the nonspecular optical energy scattered from the surface of the optical element;

a gas sample cell configured to receive and hold a gas sample in an interior region of said gas sample cell, wherein said gas sample cell is positioned in said laser resonant cavity such that said beam of optical radiation from said laser passes through said gas sample; and

a scattered light detector positioned with respect to said gas sample cell such that it receives and detects light scattered out of said laser beam by the gas sample.

2. The system of claim 1 wherein said contamination detector further comprises one of either a photodiode, a photomultiplier tube or a phototransistor.

3. The system of claim 1 wherein said contamination detector is mounted within said laser resonant cavity.

4. A method for detecting contamination of an optical element in a gas analysis system comprising the steps of:

generating a beam of laser light with a laser having a resonant cavity;

positioning the optical element in the laser resonant cavity;

irradiating the optical element with the beam of laser light;

positioning an optical contamination detector with respect to the optical element such that the optical contamination detector receives nonspecular optical radiation scattered from the beam of laser light by contamination located on a surface of the optical element;

detecting the nonspecular optical radiation scattered from the surface of the optical element;

generating an output signal which is representative of an intensity of the nonspecular optical radiation scattered from the surface of the optical element;

positioning a gas sample cell which contains a gas sample in an interior region of said gas sample cell in said laser resonant cavity such that said beam of laser light from said laser passes through the gas sample; and

receiving and detecting light scattered out of said laser beam by the gas sample with a scattered light detector.

5. The method of claim 4 wherein the step of detecting the nonspecular optical radiation further comprises the step of selecting either one of a photodiode;

a phototransistor or a photomultiplier tube.

6. The method of claim 4 wherein

the step of positioning an optical contamination detector further comprises the step of positioning the optical contamination detector within the laser resonant cavity.

7. A system for detecting contamination on a surface of an optical element in a gas analysis system comprising:

a laser having a resonant cavity, wherein said laser is disposed to generate a beam of laser light for transmission in the gas analysis system and irradiation of the optical element;

a contamination detector positioned with respect to said optical element such that it receives and detects nonspecular light scattered from the surface of the optical element;

a detector circuit operably coupled to said contamination detector to receive signals from said contamination detector which are representative of an intensity of the nonspecular light scattered from the surface of the optical element, said detector circuit having an output which produces an electronic signal which is representative of the intensity of the nonspecular light scattered from the surface of the optical element;

a gas sample cell configured to receive and hold a gas sample in an interior region of said gas sample cell, wherein said gas sample cell is positioned in said laser resonant cavity such that said beam of laser light from said laser passes through the gas sample; and

a scattered light detector positioned with respect to said gas sample cell such that it receives and detects light scattered out of said laser beam by the gas sample.

8. The system of claim 7 wherein said contamination detector further comprises one of either a ptotodiode, a photomultiplier tube or a phototransistor.

9. The system of claim 7 wherein the optical element is located within said laser resonant cavity.

10. The system of claim 7 wherein said contamination detector is mounted within said laser resonant cavity.

11. A method for detecting contamination of an optical element in a gas analysis system comprising the steps of:

generating a beam of laser light with a laser having a resonant cavity;

positioning the optical element in the laser resonant cavity;

irradiating the optical element with the beam of laser light;

positioning a contamination detector with respect to the optical element such that the contamination detector receives nonspecular reflections of optical radiation scattered from the beam of laser light by contamination located on a surface of the optical element;

detecting the nonspecular reflections of optical radiation scattered from the surface of the optical element;

generating an output signal which is representative of an intensity of the nonspecular reflections of optical radiation scattered from the surface of the optical element;

positioning a gas sample cell which is configured to receive and hold a gas sample in an interior region of the gas sample cell in the laser resonant cavity such that the beam of laser light from the laser passes through the gas sample; and

receiving and detecting light scattered out of the laser beam by the gas sample.

12. The method of claim 11 wherein the step of detecting the nonspecular reflections further comprises the step of selecting either one of a photodiode;

a phototransistor or a photomultiplier tube.

13. The method of claim 11 wherein

the step of positioning a contamination detector further comprises the step of positioning the contamination detector within the laser resonant cavity.