PRECISE FREQUENCY-MEASUREMENT OF A METHYL-ALCOHOL OPTICALLY-PUMPED LASER LINE AT 4.25 THZ

Absolute frequency measurement of the 70.5 mum wavelength (4.25 THz) l ine of a methyl alcohol (CH3OH) optically-pumped laser has been made b y 47th-harmonic mixing with a Gunn diode (90 GHz) using a Nb-Nb point- contact Josephson junction (JJ). The frequencies of the pump CO2 and t he optically-pumped CH3OH lasers are locked, respectively, on the cent er of the saturated absorption line of the methanol molecule and on th e center of the FIR laser cavity pin curve. To accurately measure the beat frequency from the JJ, a tracking oscillator is developed by mean s of the phase-lock technique. The result of 4 251 674.63 +/- 0.15 (MH z) is obtained for the center frequency of the optically-pumped laser line. The accuracy of the measurement is 3.5 X 10(-8) and is about 5 t imes more accurate than previous results.