Laser spectroscopy

• US 3,911,276 A
• Filed: 10/18/1974
• Issued: 10/07/1975
• Est. Priority Date: 10/18/1974
• Status: Expired due to Term

• Current Assignee: William E. Bell
• Original Assignee: William E. Bell
• Inventors: Bell, William E.
• Primary Examiner(s): Willis, Davis L.
• Application Number:
  US05/515,996
• Time in Patent Office: 354 Days
• Field of Search: 250/339,340,343-346 356/51,97,201,204,206
• US Class Current: 250/343
• CPC Class Codes: G01N 2021/1704 in gases
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 21/39 using tunable lasers
• CPC Class Codes: H01S 3/1055 one of the reflectors being constituted by a diffraction grating

Abstract

In laser spectroscopy, a sample medium to be analyzed, such as a gas, is interposed in a laser beam and the absorbance of energy by the sample from the laser beam is detected. In addition, the laser beam intensity is detected. A tuner is provided for tuning the wavelength of the laser beam over a plurality of discrete wavelengths to derive an absorbance spectrum of the sample under analysis. The dwell time for each of the various wavelengths of the laser beam is controlled so as to obtain equal watt-seconds of beam power at each of a number of wavelengths, whereby the sensitivity of the laser spectroscopy is normalized for the various wavelengths.

Claims

1. In a laser spectrometer:

laser means for producing a laser beam of coherent optical radiation;

sample cell means for interposing a sample medium to be analyzed in said laser beam;

detecting means for detecting the absorbance of energy, if any, by said sample medium from said laser beam;

power monitoring means for monitoring the laser beam power; and

correlating means for correlating the laser beam power for a given wavelength with the time during which the sample is being irradiated and during which the sample absorbance is detected so that the sample is irradiated with a certain predetermined watt-seconds of beam power at a given wavelength during the detection of sample absorbance, whereby the sensitivity of the laser spectrometer is normalized at said given wavelength.

2. The apparatus of claim 1 including, tuning means for varying the wavelength of the coherent optical radiation of said laser beam from a first wavelength to a second wavelength, and wherein said correlating means correlates the watt-seconds of beam power irradiating said sample during detection of absorbance at both wavelenths so that said sample is irradiated with equal watt-seconds of beam power at both of said first and second wavelengths.

3. The apparatus of claim 1 wherein said laser beam is of an infrared wavelength.

4. The apparatus of claim 1 wherein said detecting means includes, acoustic detector means coupled in acoustic wave energy exchanging relation with the sample medIum for detecting acoustic waves generated by the absorbance of laser beam energy by the sample medium.

5. The apparatus of claim 1 including, means for modulating the intensity of said laser beam.

6. The apparatus of claim 5 wherein said detecting means includes, means for synchronously detecting the absorbance of energy by the ample medium from said laser beam as a function of the modulation of the intensity of said laser beam.

7. In a method of laser spectroscopy the steps of:

interposing a sample medium to be analyzed in a laser beam;

detecting the absorbance of energy, if any, by said sample medium from said laser beam;

monitoring the laser beam power; and

correlating the laser beam power for given laser beam wavelength with the time that the sample is being irradiated and during which sample absorbance is being detected so that the sample is irradiated with a certain predetermined number of watt-seconds of beam power at a given wavelength during the detection of sample absorbance, whereby the sensitivity of the laser spectroscopy is normalized at said given wavelength.

8. The method of claim 7 including the step of, varying the wavelength of the coherent optical radiation of said laser beam from a first wavelength to a second wavelength, and wherein the step of correlating the laser beam power includes correlating the watt-seconds of beam power irradiating the sample during detection of absorbance at both wavelengths so that said sample is irradiated with equal watt-seconds of beam power at both of said first and second wavelengths.

9. The method of claim 7 wherein said laser beam is of an infrared wavelength.

10. The method of claim 7 wherein the step of detecting the sample absorbance includes the step of, coupling an acoustic wave detector in acoustic wave energy exchanging relation with the sample medium for detecting acoustic waves generated by the absorbance of laser beam energy by the sample medium.

11. The method of claim 7 including the step of modulating the intensity of the laser beam.

12. The method of claim 11 wherein the step of detecting the sample absorbance includes the step of synchronously detecting the absorbance of energy by the sample medium from the laser beam as a function of the modulation of the intensity of said laser beam.