CO-LASER SIDE-BAND SPECTROMETER - SUB-DOPPLER HETERODYNE FREQUENCY MEASUREMENTS AROUND 5 MU-M

We report the realization of a tunable sub-Doppler heterodyne spectrom eter with high absolute accuracy, employing side-band generation with a CO laser. The fixed-frequency GO-gas laser, working from 4.7 to 8.4 mu m, is made partially tunable by the use of microwave side-band gene ration in a CdTe Electro-Optical Modulator (EOM). This leads to tunabl e radiation of high spectral purity. We describe the design of the mic rowave EOM, adapted to the CO laser, its performance and its first app lication to highly accurate frequency measurements. The side-band radi ation is used for sub-Doppler stabilization of the CO laser, while the carrier frequency is mixed with the frequencies of two CO2 reference lasers. As a first result, we present measurements of OCS transitions in the 4.9 mu m (61 THz) region, reaching an absolute accuracy of 30 k Hz (Delta v/v = 5x10(-10)). Further application of our spectrometer to calibration gases will establish a variety of InfraRed (IR) calibrati on standards with a new quality of accuracy.