EFFECTIVE NOISE-REDUCTION ON PULSED-LASER EXCITATION OF MODES IN A HIGH-Q PHOTOACOUSTIC RESONATOR

An open photoacoustic detector system, consisting of a high Q cylindrical resonator (and factor in N-2 approximate to 800) and two adjoining variable acoustic filter systems, was tested for pulsed excitation of acoustical modes in a naphthalene/air gas mix by using a 308 nm excimer laser. The outside noise suppression and the signal-to-noise ratio were investigated in a normal laboratory environment in the flow-through mode. The acoustic and electric filter system combined with the averaging of the photoacoustic signal in the time domain suppresses the outside noise by 70 dB. In this case the signal-to-noise ratio was 76 dB.