Coherent microwave emission in cesium under coherent population trapping

Microwave emission has been observed at the ground-state hyperfine transiti on frequency of a cesium atomic vapor driven into a nonabsorbing state by m eans of coherent population trapping. The coherent emission observed is due to the oscillating magnetization generated by the coherence, which is indu ced between the ground-state hyperfine levels when they are coupled to an e xcited state by means of two laser radiations via a Lambda scheme. The expe riments described were done in a quartz cell containing buffer gases such a s neon and nitrogen, reducing the linewidth through the Dicke effect. The c ell was placed inside a microwave cavity tuned at 9.2 GHz, the ground-state hyperfine frequency of cesium, and a power output of the order of 100 fW w as measured in the case where nitrogen was used as the buffer gas. [S1050-2 947(99)51001-9].