Asymmetry of the saturated-absorption resonances in He — Ne/127I2 lasers pumped by a transverse rf discharge

Saturated-absorption resonances were investigated experimentally in He — Ne/¹²⁷I₂ lasers pumped by a transverse rf discharge. The much lower amplitude noise reduced sixfold the laser frequency instability, compared with the frequency instability of a laser pumped by a dc discharge, down to 5 × 10^-13 for an integration time of 100 s. The modulation shifts of the radiation frequency of stabilised He — Ne/¹²⁷I₂ lasers were investigated with a high accuracy and over a wide range of frequency deviations (1.5 — 20 MHz). The nature of the asymmetry of the saturated-absorption resonances, resulting from the joint effect of the lens-like properties of the nonlinearly absorbing medium and of the elastic velocity-changing collisions of absorbing medium molecules was clarified.