On the Theory of Femtosecond Photon Echoes from Band-to-Band Transitions in Semiconductors

A theory of femtosecond photon echo pulse decay in semiconductors is developed. The echo is due to band-to-band transitions produced by two successive pulses of coherent light. We propose that the decay is a result of the unscreened carrier-carrier interaction that brings about dephasing of the electron-hole wave function. We come to the conclusion that the time of dephasing is proportional to n-1/3, where n is the carrier concentration.