Integrated Cavity Output Spectroscopy
Integrated cavity output spectroscopy (ICOS) sometimes called as cavity-enhanced absorption spectroscopy (CEAS) records the integrated intensity behind one of the cavity mirror, while the laser is repeatedly swept across one or several cavity modes. However, for high finesse cavities the ratio of “on” and “off” a cavity mode is small, given by the inverse of the finesse, whereby the transmission as well as the integrated absorption becomes small. Off-axis ICOS (OA-ICOS) improves on this by coupling the laser light into the cavity from an angle with respect to the main axis so as do not interact with a high density of transverse modes. Although intensity fluctuations are lower than direct on-axis ICOS, the technique is, however, still limited by a low transmission and intensity fluctuations due to partly excitation of high order transverse modes, and can again typically reach sensitivities ~10−7 .
Read more about this topic: Laser Absorption Spectrometry, Cavity Enhanced Absorption Spectrometry
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