Doppler-free optical double-resonance Stark spectroscopy using modulation sidebands

Abstract

An electro‐optic modulator, driven at a single radio frequency ν, is used to create sidebands (ν_L±ν) on the frequency ν_L 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 ν_L and (ν_L±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.