Coherent population trapping resonances in thermal 85 Rb vapor: D 1 versus D 2 line excitation

We have compared coherent population trapping (CPT) resonances, both experimentally and theoretically, for excitation of the D1 and D2 transitions of thermal Rb85 vapor. Excitation of the D1 line results in greater resonance contrast than excitation of the D2 line and in a reduction in the resonance width, in agreement with theoretical expectations. These results translate into a nearly tenfold improvement in performance for the application of CPT resonances to a frequency standard or a sensitive magnetometer when the D1 line, rather than the D2 line, is used.