Gas Analysis With High-Resolution Fabry–Perot Spectrometry in the 550–650 GHz Range

The development of a high-finesse THz cavity has enabled the construction of a Fabry–Perot spectrometer. This approach can be applied to the THz frequencies (submillimeter wavelengths) allowing the rotational transitions to be probed. The intracavity power levels have permitted the sub-Doppler Lamb-dip profiles of ethanol to be observed. The quantification of a trace of H
₂
S is demonstrated with a detection limit around 60 part per billion (ppb).