ACTIVE LINE NARROWING OF A CO LASER BY FREQUENCY OFFSET LOCKING AND SATURATION LAMB DIPS OF CO AND OCS AT PRESSURES BELOW 10 PASCAL

Abstract

The Co fundamental-band laser has recently been used to define a new secondary frequency standard in the 60 THz ($5\mu$m) region [1] The passive linewidth of the CO laser is approx 220 kHz. By an active stabilization loop the CO laser could be frequency offset-locked (FOL) to two $CO_{2}$ lasers, which are stabilized to $4.3 \mu m$ saturated fluorescence Lamb dips. With a fast feedback loop the beat frequency between all three lasers could be narrowed down to 50 kHz FWHM. With a computer controlled FOL setup the CO laser is tunable within a few MHz This enhances the capabilities of our heterodyne saturation spectrometer and makes it an adequate source for the recording of sub-Doppler line shapes and small scale pressure-induced frequency shifts of CO and OCS in the pressure region below 10 Pascal.