Abstract: We report on the use of laser based cavity ring down spectroscopy in the near UV. It is this part of the spectrum that is particulary well-suited for trace gas detection, as many molecules have strong, well characterized absorption bands in this region. We show that the detection limit for e.g. NH$-3$/ is in the order of 10 ppb, for OH below 1 ppb and for Hg at the ppt level. We propose a Fourier transform based cavity ring down spectrometer, in which the advantages of cavity ring down detection are combined with the multiplex advantage of a Fourier transform spectrometer. A theoretical description of this spectrometer, as well as a proposal for the construction of a prototype are worked out. !13
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