MULTIFREQUENCY PHOTON-ECHO GENERATED BY EXTREMELY SHORT PULSES

A photon echo in a multilevel quantum medium excited by two extremely short pulses with durations of less than one period of oscillation of the light is investigated theoretically. It is shown that Q echo signa ls (Q is the number of allowed transitions) can form at each frequency of the allowed transitions, and the number of echo responses for all the allowed transitions equals Q(2). Of these, Q(Q-1) signals are sepa rated in both time and space. The other Q echo signals of all the allo wed frequencies all arise at the time 2 tau(21) (tau(21) is the time i nter val between application of the first and second pulses to the med ium) and are collinear with one another. (C) 1998 American institute o f Physics. [S0021-3640(98)01011-1].