National Research Council of Canada. NRC Herzberg Institute of Astrophysics
An electro‐optic modulator, driven at a single radio frequency ν, is used to create sidebands (νL±ν) on the frequency νL of a cw single‐mode CO2 laser. Laser‐induced line narrowing in molecular Stark spectroscopy is demonstrated, using double resonances of the copropagating waves at νL and (νL±ν) with pairs of coupled Doppler‐broadened transitions. Doppler‐free Stark spectra of the molecules PH3, 13CH3F, and 12CH3F are used to illustrate the technique. For PH3 it is found that the electric dipole moment vibrational difference ‖μ (v2=1)−μ (v=0) ‖⩽0.005 D.