Waveguide CO2/OsO4 laser with a frequency stability of 10–13

A high-pressure waveguide CO₂ laser was stabilized using the resonance frequency of saturated absorption due to the A²₂P(46) transition in the ν₃ band of ¹⁹²OsO₄ (28.46 THz). The laser had a preliminary frequency stabilization system based on a transmission resonance of an external Fabry–Perot interferometer, narrowing the emission spectrum to 1 kHz. An external absorption cell was used: it contained OsO₄ vapor at a reduced pressure. The frequency instability was measured by comparison with the frequency of a low-pressure CO₂/OsO₄ laser stabilized using a resonance located at the center of the CO₂ P(14) line. The relative instability of the frequencies of the lasers was 10^–13(τ^–1+2τ⁰) for values of τ from 1 msec to 400 sec. The long-term stability (flicker limit) of ~10^–13 was probably governed by pulling effects arising, in particular, from parasitic reflections in the optical system.