Abstract

We show experimentally that two-photon absorption (TPA) in semiconductors is maximized by the shortest possible, bandwidth-limited laser pulse, unperturbed by non-trivial phase effects. Such effects have been observed in atomic systems, in which the TPA probability for certain non-bandwidth-limited pulses can be as high¹ or even higher² than for bandwith-limited ones. For semiconductors, these effects cannot easily be ruled out on theoretical grounds. Our experimental work demonstrates that TPA signals from semiconductors yield a reliable merit function for adaptive pulse compression^3,4 since TPA is maximized by the shortest possible pulse. Reliable and accurate adaptive compression of broadband laser pulses has been achieved in photoluminescence experiments on CdS thin films and in photocurrent experiments on a GaAsP photodiode. For broadband pulses, TPA is an easy-to-imple- ment alternative to second harmonic generation (SHG), which is routinely used for adaptive compression.^3,4 In particular, TPA offers the advantage that it does not require phase-matching, which is difficult to achieve over a large bandwidth in SHG experiments. Moreover, using TPA in photodiodes, a very compact set-up is obtained.

© 2002 Optical Society of America