Frequency Stabilization of CH₃OH Laser at 469 µm to Millimeter-Wave Frequency Standard

Frequency stabilization of an optically-pumped CH 3 OH laser oscillating in the 469 µm line to a phase-locked 71 GHz reference was investigated. The CO 2 pump laser was offset-locked to the 4.3 µm-fluorescence stabilized CO 2 laser. A frequency stability σ y (τ) of 2×10 -11 in terms of the square root of the Allan variance was obtained at 469 µm, where τ is the averaging time. The stability is discussed in conjunction with the dispersion effect of the oscillation frequency due to variation of the pump frequency and also with the oscillation frequency shift due to variation of the pump power.