Tunable two-mode Cr2+ : ZnSe laser with a frequency-noise spectral density of 0.03 Hz Hz-1/2

An optically pumped cw laser on a Cr²⁺ : ZnSe crystal with a tunable (in the range of 2.3 — 2 .6 mm) wavelength, operating with generation of two axial modes, has been developed. It is shown that the minimum laser frequency-noise spectral density does not exceed 0.03 Hz Hz^-1/2. Application of this laser in problems of Doppler and Doppler-free spectroscopy makes it possible to detect spectral absorption lines of gases with sensitivities of 5 × 10^-12 and 2 × 10^-10 cm^-1, respectively (averaging time τ = 1 s). Having stabilised this laser with respect to the Doppler-free resonances of saturated dispersion of methane molecule, one can obtain a short-term frequency stability of 10^-15 — 10^-16 (τ = 1 s).