Off-axis integrated cavity output spectroscopy and its application

Based upon the property of optical cavity and the principle of signals and systems, the measural theory and signal expression of off-axis integrated cavity output spectroscopy (Off-axis ICOS) have been analyzed and deduced. A compact and low-cost Off-axis ICOS apparatus, which used a special circuit to integrate the cavity output signal, was then described and experimented. The absorption spectrum of water vapor in the spectral range of 6587∼6595.5 cm−1 was measured with this Off-axis ICOS system, and the measured spectral parameters were compared with the results of continuous-wave cavity ring down spectroscopy (CW-CRDS) and HITRAN2004 database. The detectable sensitivity of the system was achieved as ∼2.8 × 10−9 cm−1.