Cr:ZnSe laser with 0.03 Hz/Hz1/2 frequency noise for compact methane based OFS

The mid-IR cw tunable solid state Cr
²⁺
:ZnSe laser with spectral density of intrinsic frequency noise less than 30 mHz/Hz
^1/2
was created. The laser was applied for sub-Doppler spectroscopy of (ν
₁
+ν
₄
) vibrational-rotational band of methane and narrow resonances of saturated dispersion at λ = 2.36 μm were demonstrated for the first time. Characteristics of resonances and low frequency noise of the laser pave the way to a short-term frequency stability at the level of 10
^-15
- 10
^-16
.