Abstract

A cesium cell illuminated by two laser light beams resonant with the D₂ transition becomes transparent when the laser difference frequency corresponds to the 9.2 GHz hyperfine splitting: the coherent population trapping resonance. When the two lasers have different intensities the minimum of the absorption shifts with intensity. Using an optical phase-locked loop to control the laser difference frequency we can obtain linewidths of 10 kHz for simple vapor cells and less than 50Hz for cells with neon as a buffer gas [1], allowing a precise determination of the resonance shift. Fig. 1 shows the shift of the resonance position vs. laser intensity for two different experimental conditions (squares and circles).

© 1998 IEEE