A NEW KIND OF HETERODYNE MEASUREMENT OF COHERENT POPULATION TRAPPING IN AN ATOMIC-BEAM

A new heterodyne technique is presented for the simultaneous measureme nt of dispersion and absorption of atomic transitions useful especiall y for coherent two photon transitions. This technique is compared with traditional homodyne interferometer and with modem frequency modulati on techniques. First results are the properties of a coherent populati on trapping (CPT) scheme realized in a cesium atomic beam. The measure d linewidth of the CPT-resonance is similar or equal to 300 kHz (FWHM) with a residual absorption of less than 2 x 10(-3) cm(-1) and the dis persion is equivalent to a group velocity of upsilon(s) approximate to c/5000.