An improved CO2 laser intracavity photoacoustic spectrometer for trace gas analysis

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Abstract
This work describes an improved CO2 laser intracavity photoacoustic spectrometer. It can detect and measure small quantities of trace gases in air. The measured absorption sensitivity of 3.3×10−10 cm−1 corresponds to a mixture of 11 pptv (volume parts per trillion) of ethene in nitrogen. The sensitivity and reliability of the instrument were enhanced by reducing the level of background signals originating from optical and acoustical sources. The sensitivity reached is comparable with the best existing continuous measuring instruments while the background signal is two orders of magnitude smaller. The improvements are described in detail and a comparison to previous work is made. A first measurement demonstrates the suitability of the apparatus for biological applications.