Investigation of cw dye laser frequency locking by atomic absorption lines

An investigation was made of the phenomenon of frequency locking of radiation from a cw dye laser by absorption lines of neon and helium in a gas discharge. In the locking regime the emission frequency depended on the discharge current and the gas pressure. On varying the current in the range 5–30 mA, the frequency detuning from the center of the absorption line increased linearly from 40 to 170 GHz. A change in the gas pressure from 1.5 to 5 Torr caused a nonmonotonic change in the detuning. A frequency locking model was proposed for the conditions realized experimentally, according to which the locked frequency is determined by a lens formed by a radial inhomogeneity of the refractive index in the gas disharge, while spectral narrowing in the locking regime is explained by nonlinear processes occurring when intense laser radiation interacts with an absorbing gas.