  Intracavity laser absorption spectroscopy (ICLAS) with an evacuated Cr2+:
ZnSe laser is performed with a high-resolution time-resolved Fourier transform
interferometer with a minimum detectable absorption coefficient equal to 4 10-9
cm-1 Hz-1/2 in the 2.5$\mu$m region. This represents the extreme limit
presently reached in the infrared by ICLAS with Doppler limited resolution. The
broad gain band of the crystal allows a spectral coverage at most equal to 125
nm, wide enough to see entire vibration bands. Weak CO2 bands observed up to
now only in the Venus atmosphere are recorded for the first time in a
laboratory. H2O detection limit down to 0.9 ppbv is also demonstrated.
