Photoacoustic spectroscopy system and technique for remote sensing of explosives and toxic chemicals

• US 20080180675A1
• Filed: 01/29/2007
• Published: 07/31/2008
• Est. Priority Date: 01/29/2007
• Status: Active Grant

• Current Assignee: UChicago Argonne LLC (University of Chicago)
• Original Assignee: UChicago Argonne LLC (University of Chicago)
• Inventors: Raptis, Apostolos C., Sheen, Shuh-Haw, Chien, Hual-Te
• Granted Patent: US 7,644,606 B2
• Time in Patent Office: Days
• US Class Current: 356/437
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 2291/014 Resonance or resonant frequency
• CPC Class Codes: G01N 2291/0255 (Bio)chemical reactions, e.g. on biosensors
• 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 user-friendly photoacoustic spectroscopy (PAS) system and process (technique) provides an open-field PAS instrument, unit and device to remotely sense explosives, chemicals and biological agents. The PAS system and process can include: a pulsed tunable laser, such as a CO₂ laser, a reflector, such as a parabolic reflector, an acoustic reverberant resonator in which a microphone is installed, and a data acquisition and analysis system.

Claims

1. A photoacoustic spectroscopy (PAS) system for remote sensing of explosives, toxic chemicals, and biological agents, or other material, comprising:

a tunable laser for transmitting optical energy comprising laser pulses at a selected frequency to a remote target comprising explosives, toxic chemicals, biological agents, or other material, and causing acoustic signals to be emitted from the target;

a pulse generator comprising a chopper operating at a frequency selected on the basis of background noise for generating pulses to said tunable laser;

a sensor for detecting acoustical signals from the target;

a reflector for receiving acoustic signals from the target and focusing the acoustic signals to a focal area comprising said sensor;

a resonator for reducing acoustic interference and amplifying the acoustic signals; and

data acquisition and analysis equipment operatively connected and cooperating with said sensor, reflector, resonator, tunable laser, and pulse generator, for determining information about the target.

2. A PAS system in accordance with claim 1 wherein said tunable laser is selected from the group consisting of a pulsed laser, modulated laser, carbon dioxide (CO₂) laser, an ultraviolet (UV) laser, excimer laser, helium cadmium (HeCd) laser, solid state laser, diode laser, ion laser, and fiber laser.

3. A PAS system in accordance with claim 1 wherein:

said tunable laser is a carbon dioxide (CO₂) infrared (IR) laser; and

said explosives are selected from the group consisting of nitroglycerine (NG), ethylene glycol dinitrate (EGNG), dinitroltoluene (DNT), trinitrotoluene (TNT), and ammonium nitrate (NH₄NO₃).

4. A PAS system in accordance with claim 1 including:

a laser guiding and tracking system operatively coupled to said tunable laser; and

said laser guiding and tracking system comprising said sensor and a visible helium neon (He/Ne) laser.

5. A PAS system in accordance with claim 1 wherein said reflector comprises a parabolic reflector having a diameter proportional to a distance to the target.

6. A PAS system in accordance with claim 1 wherein:

said laser comprises a ultraviolet (UV) laser;

said target comprises a biological agent;

said reflector comprises a parabolic mirror; and

said PAS system includes an optical sensor positioned in said resonator.

7. A PAS system in accordance with claim 1 wherein:

said data acquisition and analysis equipment comprises a photoacoustic spectrometer and/or a central processing unit (CPU) and a screen for displaying real-time frequency-domain signals; and

said CPU is selected from the group consisting of a wireless microprocessor, hardwired microprocessor, laptop, portable computer, desktop computer, cell phone, iPod, Palm Pilot, Blackberry, mobile communications apparatus, and electronic handheld device.

8. A PAS system in accordance with claim 1 wherein said resonator comprises a cylindrical tube resonator having a resonant frequency equaling the chopper frequency.

9. A PAS system in accordance with claim 1 wherein said resonator comprises an acoustic reverberant resonator.

10. A PAS system in accordance with claim 9 including:

a microphone positioned in proximity to said resonator for receiving the acoustic signals from the target;

an optical fiber amplifier positioned downstream of said laser; and

a power meter operatively associated with said optical fiber amplifier; and

said other material is selected from the group consisting of gases, liquids, solids, and surface contamination.

11. A PAS system in accordance with claim 10 wherein:

said resonator comprises a tunable acoustic reverberant resonator and can be tuned to a specific resonant frequency and operate in a open field or area;

said resonator comprising a negative expansion chamber having a area equaling the focal area of the reflector; and

said microphone is mounted flush to an inside wall of the reflector at a position to optimize detection of the signal at the resonant frequency.

12. A photoacoustic spectroscopy (PAS) process for remote sensing of explosives, toxic chemicals, and biological agents, or other material, comprising:

transmitting optical energy comprising laser pulses at a selected frequency from a tunable laser to a remote target comprising explosives, toxic chemicals, biological agents, or other material;

emitting acoustic signals from the target;

scanning background noise;

operating a pulse generator comprising a chopper at a frequency in a region of least noise selected on the basis of the scanned background noise;

generating pulses to the tunable laser;

detecting acoustical signals from the target with a sensor;

receiving acoustic signals from the target on a reflector;

focusing the acoustic signals to a focal area comprising the sensor;

reducing acoustic interference with a resonator;

amplifying the acoustic signals;

adjusting the resonator to resonate the frequency of the chopper; and

determining information about the target with data acquisition and analysis equipment.

13. A PAS process in accordance with claim 12 for use in detecting explosives, wherein:

said explosives are selected from the group consisting of nitroglycerine (NG), ethylene glycol dinitrate (EGNG), dinitroltoluene (DNT), trinitrotoluene (TNT), and ammonium nitrate (NH₄NO₃); and

said tunable laser is a carbon dioxide (CO₂) infrared (IR) laser.

14. A PAS process in accordance with claim 12 for use in detecting biological agents, wherein:

said laser comprises a ultraviolet (UV) laser;

said reflector comprises a parabolic mirror; and

an optical sensor is positioned in the resonator.

15. A PAS process in accordance with claim 12 for use in detecting toxic chemicals, wherein:

said tunable laser is selected from the group consisting of a pulsed laser, modulated laser, carbon dioxide (CO₂) laser, an ultraviolet (UV) laser, excimer laser, helium cadmium (HeCd) laser, solid state laser, diode laser, ion laser, and a fiber laser.

16. A PAS process in accordance with claim 12 for use in detecting trace gases, liquids, solids, surface contamination, poisons, surface contamination, or other hazardous material including displaying real-time frequency-domain signals.

17. A PAS process in accordance with claim 12, including laser guiding and tracking with the sensor and a visible He/Ne laser.