Stabilization of 48- and 57-µm CH3OD lasers pumped by 9R(8) CO2 laser for two color interferometer

A two color far-infrared (FIR) laser interferometer of beat modulation type using 48- and 57-mum CH₃OD lasers pumped by 9R(8) CO₂ laser has been developing for plasma diagnostics. The pump 9R(8) CO₂ laser frequency, 48- and 57-mum CH₃OD laser outputs and FIR beat frequency have been stabilized preliminary. The power stability of pump CO₂ laser of < plusmn 0.6 % and the frequency stability of < plusmn 0.78 MHz at the line center for 40 min. have been obtained by using external Stark cell modulation. For the twin type FIR laser system, an output stability of plusmn 2.4 % and an beat signal frequency of 765 plusmn 27 kHz for 40 min. have been obtained by controlling the cavity length for the 57-mum CH₃OD laser.