Mode by Mode CW-CRDS at 80 K: Application to the 1.58 μm transparency window of CH4

A cryogenic cell has been specifically developed for CW-Cavity Ring Down Spectroscopy (CRDS) down at liquid nitrogen temperature (77 K). It is based on an original design which dispenses with an external vacuum jacket. A Mode by Mode CRDS acquisition scheme has been used to get rid of the piezoelectric actuator that modulates the optical cavity length in standard CW-CRDS. This new scheme leads to a sensitivity equivalent to that achieved at room temperature (αmin ∼ 3 × 10–10 cm–1). The first CRDS spectrum of methane cooled down to liquid nitrogen temperature has been recorded in the region of the 1.58 μm methane transparency window, of particular interest for planetary science.