Method for increasng the dynamic range of a cavity enhanced optical spectrometer

• US 20060082778A1
• Filed: 10/14/2004
• Published: 04/20/2006
• Est. Priority Date: 10/14/2004
• Status: Active Grant

• Current Assignee: Picarro, Inc.
• Original Assignee: Picarro, Inc.
• Inventors: Paldus, Barbara, Kachanov, Alexander, Crosson, Eric, Richman, Bruce
• Granted Patent: US 7,265,842 B2
• Time in Patent Office: Days
• US Class Current: 356/437
• CPC Class Codes: G01N 21/39 using tunable lasers

Abstract

A gaseous target analyte present as a minor constituent in an admixture with at least one other gaseous species can be detected using a cavity enhanced optical spectrometer by a process comprising the steps of: i) identifying a plurality of strong spectral absorption peaks of the target analyte which are present within the scanning range of the spectrometer, ii) determining for the identified peaks the pressure region above which the peak width increases substantially with increasing pressure and below which the peak width is substantially independent of pressure, iii) determining which of the peaks identified in step i) are, within the pressure region determined in step ii), free from spectral interference by any of the other components of the admixture. iv) measuring the spectrum of the admixture at the pressure region identified in step ii).

Claims

1. A process for detecting a gaseous target analyte present as a minor constituent in an admixture with at least one other gaseous species using a cavity enhanced optical spectrometer comprising the steps of:

i) identifying a plurality of strong spectral absorption peaks of said target analyte which are present within the scanning range of said spectrometer,

ii) determining for said identified peaks the pressure region above which the peak width increases substantially with increasing pressure and below which the peak width is substantially independent of pressure,

iii) determining which of the peaks identified in step i) are, within the pressure region determined in step ii), free from spectral interference by any of the other components of said admixture.

iv) Measuring the spectrum of said admixture at the pressure region identified in step ii).

4. A process in accordance with claim 1 comprising the additional step of increasing the pressure to the maximum extent possible without causing at least one of the peaks identified in step iii) to overlap with an absorption peak of any of the other components of said admixture.

6. A process in accordance with claim 1 wherein said spectrometer utilizes as a light source at least one Distributed Bragg reflector Laser, Optical Parametric Oscillator, Optical Parametric Generator, Optical Parametric Amplifier, External Cavity Diode Laser, Distributed Feedback Laser or Quantum Cascade Laser.

7. A process in accordance with claim 6 wherein the laser used in said spectrometer is a Distributed Feedback Laser.

2. A process for detecting a gaseous target analyte present as a minor constituent in an admixture with at least one other gaseous species using a cavity enhanced optical spectrometer comprising the steps of:

i) identifying a plurality of strong spectral absorption peaks of said target analyte which are present within the scanning range of said spectrometer,

ii) determining for said identified peaks the pressure region above which the peak height is substantially independent of pressure and below which the peak height decreases substantially with decreasing pressure,

iii) determining which of the peaks identified in step i) are, within the pressure region determined in step ii), free from spectral interference by any of the other components of said admixture.

iv) Measuring the spectrum of said admixture at the pressure region identified in step ii).

5. A process in accordance with claim 2 comprising the additional step of increasing the pressure to the maximum extent possible without causing at least one of the peaks identified in step iii) to overlap with an absorption peak of any of the other components of said admixture.

8. A process in accordance with claim 2 wherein said spectrometer utilizes as a light source at least one Distributed Bragg reflector Laser, Optical Parametric Oscillator, Optical Parametric Generator, Optical Parametric Amplifier, External Cavity Diode Laser, Distributed Feedback Laser or Quantum Cascade Laser.

9. A process in accordance with claim 8 wherein the laser used in said spectrometer is a Distributed Feedback Laser

13. A process in accordance with claim 2 wherein at least one of the at least one other gaseous species in the admixture manifests a high continuum background absorption comprising identifying which of the peaks identified in step iii) minimize the background continuum and show a maximum peak height for the target analyte.

3. A process for detecting a gaseous target analyte present as a minor constituent in an admixture with at least one other gaseous species using a cavity enhanced optical spectrometer comprising the steps of:

i) identifying a plurality of strong spectral absorption peaks of said target analyte which are present within the scanning range of said spectrometer,

ii) determining for said identified peaks the pressure region above which the peak width increases substantially with increasing pressure and below which the peak width is substantially independent of pressure,

iii) determining if any of the peaks identified in step i) are, within the pressure region determined in step ii), free from spectral interference by absorption peaks of any of the other components of said admixture, and if none of said identified peaks are interference free, reducing the pressure to an extent sufficient to minimize overlap with the interfering absorption peaks.

iv) Measuring the spectrum of said admixture at the pressure region identified in step ii).

10. A process in accordance with claim 3 wherein said spectrometer utilizes as a light source at least one Distributed Bragg reflector Laser, Optical Parametric Oscillator, Optical Parametric Amplifier, Optical Parametric Generator, External Cavity Diode Laser, Distributed Feedback Laser or Quantum Cascade Laser.

11. A process in accordance with claim 10 wherein the laser used in said spectrometer is a DFB laser.

14. A process in accordance with claim 3 wherein at least one of the at least one other gaseous species in the admixture manifests a high continuum background absorption comprising identifying which of the peaks identified in step iii) minimize the background continuum and show a maximum peak height for the target analyte.

12. A process in accordance with claim I wherein at least one of the at least one other gaseous species in the admixture manifests a high continuum background absorption comprising identifying which of the peaks identified in step iii) minimize the background continuum and show a maximum peak height for the target analyte.