A new kind of heterodyne measurement of coherent population trapping in an atomic beam

A new heterodyne technique is presented for the simultaneous measurement of dispersion and absorption of atomic transitions useful especially for coherent two photon transitions. This technique is compared with traditional homodyne interferometer and with modern frequency modulation techniques. First results are the properties of a coherent population trapping (CPT) scheme realized in a cesium atomic beam. The measured linewidth of the CPT-resonance is reverse similar, equals 300 kHz (FWHM) with a residual absorption of less than 2 × 10−3 cm−1 and the dispersion is equivalent to a group velocity of vg ≈ c/5000