PHOTON-ECHOES AND BERRYS PHASE

We prove a theorem linking the phase associated with the ballistic evo lution of a coherent state of a harmonic oscillator about a jumping ve rtex to that associated with its adiabatic migration along straight li nes connecting the initial and the final points of each ballistic are to the vertex on which the are is centered. This equivalence allows on e to determine the ballistic phase by Berry's prescription. The method facilitates both the visualization and the calculation of modulation effects (quantum beats) in photon-echo experiments.