PHOTOACOUSTIC POINT SPECTROSCOPY

• US 20100033722A1
• Filed: 08/11/2008
• Published: 02/11/2010
• Est. Priority Date: 08/11/2008
• Status: Active Grant

• Current Assignee: University of Tennessee Research Foundation (University of Teesside), UT-Battelle LLC
• Original Assignee: UT-Battelle LLC
• Inventors: Van Neste, Charles W., Thundat, Thomas G., Senesac, Lawrence R.
• Granted Patent: US 7,961,313 B2
• Time in Patent Office: Days
• US Class Current: 356/432
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 29/2418 using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046

Abstract

A system and method are disclosed for generating a photoacoustic spectrum in an open or closed environment with reduced noise. A source may emit a beam to a target substance coated on a detector that measures acoustic waves generated as a result of a light beam being absorbed by the target substance. By emitting a chopped/pulsed light beam to the target substance on the detector, it may be possible to determine the target'"'"'s optical absorbance as the wavelength of light is changed. Rejection may decrease the intensity of the acoustic waves on the detector while absorption may increase the intensity. Accordingly, an identifying spectrum of the target may be made with the intensity variation of the detector as a function of illuminating wavelength.

Claims

1. An apparatus for point spectroscopy comprising:

a light source;

a vibratory detector that measures the optical beam from the light source;

an optical beam emitted from the light source that is chopped or pulsed at an optical frequency; and

a target material that is coupled with the detector that reacts to the optical beam, wherein the reaction is measured by a photoacoustic induced vibration of the detector as the optical frequency is changed.

2. The apparatus of claim 1 wherein the reaction comprises an acoustic wave that is generated on the surface of the detector from the incident optical beam and that is measured by the detector.

3. The apparatus of claim 1 wherein the optical frequency corresponds with a resonant frequency of the detector.

4. The apparatus of claim 3 wherein the detector comprises any mechanical resonator, wherein the optical frequency corresponds with a resonant frequency of the mechanical resonator.

5. The apparatus of claim 4 wherein the detector comprises a tuning fork, wherein the resonant frequency corresponds with a resonant frequency of the tuning fork.

6. The apparatus of claim 1 wherein the detector comprises a photocell configured to measure an intensity of the optical beam.

7. The apparatus of claim 1 wherein the target material is coated or covered over the detector.

8. A system for point spectroscopy comprising:

a source array comprising a plurality of sources that each emit a pulsed light beam at a predetermined frequency;

a detector array comprising a plurality of detectors that each have a predetermined resonant frequency, wherein the resonant frequency for each of the detectors corresponds with the predetermined frequency from at least one of the sources; and

a target material that is coupled with one or more detectors in the array that reacts to the pulsed light beams, wherein the reaction comprises a photoacoustic induced vibration of the corresponding detector that is measured as the optical frequency is changed.

9. The system of claim 8 wherein the measurement at each of the detectors comprises an acoustic or vibrational measurement generated on the surface of the detector.

10. The system of claim 9 wherein a spectrum of the measurement is generated based on the measured vibrational intensity at the predetermined frequencies of each of the sources.

11. The system of claim 8 wherein the target material is coated or covered on the one or more detectors in the array.

12. The system of claim 8 wherein the source array comprises a plurality of light sources or a single source with a grating that produces individual optical wavelengths corresponding to the detectors in the detector array, further wherein the detector array comprises a mechanical resonator.

13. A method for point spectroscopy comprising:

providing a light source;

chopping light emitted from the light source at a predetermined frequency;

directing the emitted light to a target coated on a detector, wherein the target reacts to the emitted light;

measuring the reaction at the detector to the emitted light; and

measuring the reaction at the detector to the emitted light as the chopping frequency is adjusted.

14. The method of claim 13 wherein the reaction comprises an acoustic wave that is generated on a surface of the detector.

15. The method of claim 14 wherein the measuring the reaction comprises measuring the acoustic wave that is generated on the surface of the detector.

16. The method of claim 13 wherein the measurement comprises measuring a photoacoustic induced vibration of the detector as the chopping frequency is adjusted.

17. The method of claim 13 further comprising analyzing the measurements to identify the target.

18. The method of claim 13 wherein the chopping frequency is substantially similar to a resonant frequency of the detector.

19. A point spectroscopy system comprising:

a quantum cascade laser light source that transmits pulsed light at an optical frequency;

a target that is subject to the light source, wherein the pulsed light on the target generates a reaction; and

a quartz crystal tuning fork coupled with the target that is used as a detector to measure the reaction to the pulsed light from the target, wherein the reaction comprises a photoacoustic wave that is produced on the surface of the quartz crystal tuning fork creating a mechanical vibration measured by the quartz crystal tuning fork.

20. The system of claim 19 wherein the target comprises a material that is coated on the quartz crystal tuning fork.

21. The system of claim 19 wherein an amplitude of the vibration of the quartz crystal tuning fork is measured as the optical frequency of the pulsed light is varied to generate a spectrum.