AN IMPROVED CO2-LASER INTRACAVITY PHOTOACOUSTIC SPECTROMETER FOR TRACE GAS-ANALYSIS

This work describes an improved CO2 laser intracavity photoacoustic sp ectrometer. It can detect and measure small quantities of trace gases in air. The measured absorption sensitivity of 3.3x10(-10) cm(-1) corr esponds to a mixture of 11 pptv (volume parts per trillion) of ethene in nitrogen. The sensitivity and reliability of the instrument were en hanced by reducing the level of background signals originating from op tical and acoustical sources. The sensitivity reached is comparable wi th the best existing continuous measuring instruments while the backgr ound signal is two orders of magnitude smaller. The improvements are d escribed in detail and a comparison to previous work is made. A first measurement demonstrates the suitability of the apparatus for biologic al applications. (C) 1996 American Institute of Physics.