Optimization of CO/sub 2/ laser frequency stabilization via external Doppler dither modulation

An external Doppler dither modulation scheme for locking the CO/sub 2/ laser frequency to the center of the 4.2- mu m fluorescence Lamb dip of CO/sub 2/ is discussed. The optimum values for the frequency dither, fluorescence cell temperature and CO/sub 2/ absorber gas pressure depending on the experimental conditions are determined. The design of two different dither mirror arrangements is described. With optimum parameters and with tau =40 ms integration time, it is possible to lock the CO/sub 2/ laser to within +or-10 kHz to line center over several minutes. Measurements of ultrahigh-resolution Lamb dip spectra of the upsilon /sub 2/ as R