A Highly Stabilized Semiconductor Laser and Its Application to Optically Pumped Rb Atomic Clock

Abstract

Frequency stability of 1 x 1 0-1 at T = 100 S was obtained for 0.8 u m AlGaAs laser by using spectral lines of Rb vapor as frequency references. It was confirmed that this value of the stability was as high as the value limited by spontaneous emission noise. Through an analysis based on a semiclassical Langevints equation, it was estimated that the stability can be improved to as high as reduction was also tried to improve the coherence of the semiconductor laser. A novel technique, i.e., electrical feedback, was proposed for this reduction instead of using a conventional technique of optical feedback. The linewidth was stably reduced by this technique. The minimum value obtained was 330 kHz for an InGaAsP laser at 1.5 p m, which was fifteen times narrower than that of a free-running laser. It was estimated that the linewidth can be ultimatelyreducedtoa value less than 1 kHz by this technique. Experiments on optical pumping for Rb atomic clock were carried out by using the highly stabilized semiconductor laser mentioned above. As the first step, experiments on saturated absorption spectroscopy of 87Rb D2 lines were carried out. Eleven lines, including cross-resonance lines, were clearly observed. As the next step, double resonance signal was obtained by laser optical pumping. The microwave frequency shift by the laser frequency and power were measured. The microwave frequency stability was also evaluated. Furthermore, a comment on the spectral lifetime of semiconductor laser for Rb atomic clock was given. 1.7 x 10-14 -112. Spectral linewidth