Variable-length cell for studies of gas spectra with extremely short optical paths

We present a cell for studies of light transmission through very strongly absorbing gases. It uses a fixed window and a mirror, parallel to the latter and attached to a micrometric linear motion feedthrough monitoring mirror-window distances from 0 to a couple of centimeters. This device is tested by recording CO₂gas spectra near 4.3 μm using a Fourier transform spectrometer. Their analysis shows that optical-path lengths between20 and 2000μm have been obtained. This now enables spectroscopic measurements of self-broadening coefficients of ¹⁶O¹²C¹⁶O lines in the ν₃band, for instance, and opens perspectives for optical soundings of thin films of porous materials.