Quartz-enhanced photoacoustic spectroscopy

• US 20050117155A1
• Filed: 06/10/2003
• Published: 06/02/2005
• Est. Priority Date: 06/10/2002
• Status: Active Grant

• Current Assignee: Rice University
• Original Assignee: Rice University
• Inventors: Kosterev, Anatoliy A.
• Granted Patent: US 7,245,380 B2
• Time in Patent Office: Days
• US Class Current: 356/432
• CPC Class Codes: G01N 2021/1704 in gases
• CPC Class Codes: G01N 2021/1708 with piezotransducers
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 2291/0427 Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
• CPC Class Codes: G01N 29/2425 optoacoustic fluid cells therefor

Abstract

Methods and apparatus for detecting photoacoustic signals in fluid media are described. The present invention differs from conventional photoacoustic spectroscopy in that rather than accumulating the absorbed energy in the fluid of a sample cell, the absorbed energy is accumulated in an acoustic detector or sensitive element. In a preferred embodiment, the acoustic detector comprises piezoelectric crystal quartz. The quartz is preferably in the shape of a tuning fork.

Claims

1. A method for performing photoacoustic spectroscopy (PAS) of a sample, the method comprising:

(a) providing a light source configured to introduce light having at least one wavelength into the sample such that at least one molecule within the sample is stimulated, generating an acoustic signal;

(b) accumulating the acoustic signal in a resonant acoustic detector; and

(c) displaying an output signal indicative of the acoustic signal.

2. The method according to claim 1 wherein the wavelength of the light in step (a) is selected such that the molecule resonates at the wavelength.

3. The method according to claim 1 wherein the light provided in step (a) is modulated at a resonant acoustic frequency f.

4. The method according to claim 3 wherein the acoustic detector resonates at the resonant acoustic frequency f.

5. The method according to claim 4 wherein the acoustic detector accumulates the acoustic signals during a predetermined number of oscillation periods Q.

6. The method according to claim 5 wherein Q and f are related by the equation t=Q/f, with t being the time it takes the acoustic detector to accumulate one acoustic signal.

7. The method according to claim 6 wherein Q is less than 8,000.

8. The method according to claim 1, further including the steps of converting said acoustic signal to an electric signal and amplifying at least one of the signals, prior to step (c).

9. The method according to claim 1 wherein the light source is a laser.

10. The method according to claim 1 wherein the acoustic detector comprises a low-loss crystal material shaped into a resonant element.

11. The method according to claim 9 wherein the material is piezoelectric quartz.

12. The method according to claim 10 wherein the quartz resonant element is a tuning fork.

13. A photoacoustic spectroscopy (PAS) system for detecting an acoustic signal, the system comprising an acoustic detector, wherein the acoustic detector accumulates at least one resonant acoustic signal and emits an electrical signal corresponding to the acoustic signal.

14. The system according to claim 13 further comprising a preamplifier connected to the acoustic detector, wherein the preamplifier amplifies at least one of the signals.

15. An acoustic detector comprising a piezoelectric material, the piezoelectric material configured to accumulate acoustic signals.