Time-resolved Fourier transform intracavity spectroscopy with a Cr^2+:ZnSe laser

Intracavity laser absorption spectroscopy (ICLAS) with an evacuated ${\mathrm{Cr}}^{2+}:\mathrm{Zn}\mathrm{Se}$ laser is performed with a high-resolution time-resolved Fourier transform interferometer with a minimum detectable absorption coefficient equal to $4\times {10}^{-9}{\mathrm{cm}}^{-1}{\mathrm{Hz}}^{-1∕2}$ in the $2.5\mu \mathrm{m}$ region. This represents the extreme limit currently 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 $125\mathrm{nm}$, wide enough to see entire vibration bands. Weak $\mathrm{C}{\mathrm{O}}_2$ bands observed up to now only in the Venusian atmosphere are recorded for the first time, to our knowledge, in a laboratory. An ${\mathrm{H}}_2\mathrm{O}$ detection limit down to 0.9 parts per billion by volume is also demonstrated.