Patent ID: 7644606

Claim:
A photoacoustic spectroscopy (PAS) system for remote sensing of a remote target comprising chemicals providing explosives, comprising: a tunable laser for transmitting optical energy comprising laser pulses at a selected frequency to the remote target 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 parabolic reflector for receiving acoustic signals from the target and focusing the acoustic signals to a focal area comprising said sensor; a cylindrical resonator for reducing acoustic interference and amplifying the acoustic signals, said cylindrical resonator providing an acoustic reverberant resonator comprising a cylindrical tube having an open end and a partially blocked end, the open end of the cylindrical tube being positioned at the local length of the parabolic reflector, the cylindrical tube being elongated and extending a length, the length of the cylindrical tube being adjustable to match a resonance condition in which the length of the cylindrical tube is equal to a multiple number of half acoustic wavelength according to the formula l=nλ/ 2 wherein l=length of the cylindrical tube n=integer λ=wavelength and the wavelength is equal to the sound velocity divided by a laser chopper frequency; 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.