We report on two-photon detection based on nonlinear absorption between subbands in quantum wells. Resonantly enhanced nonlinear absorption, 6 orders of magnitude higher than that of typical bulk semiconductors, leads to a threshold power density for quadratic detection as low as 0.1 W/cm^2 and to femtosecond time resolution. The approach facilitates dynamic characterization of the optical light field of infrared emitters with unprecedented sensitivity. We also present a new method for determining the intersubband and intrasubband scattering times by means of autocorrelation measurements.
© 2005 Optical Society of America
(040.4200) Detectors : Multiple quantum well
(190.5970) Nonlinear optics : Semiconductor nonlinear optics including MQW
(320.7080) Ultrafast optics : Ultrafast devices
(320.7130) Ultrafast optics : Ultrafast processes in condensed matter, including semiconductors
Harald Schneider, Thomas Maier, H. C. Liu, Martin Walther, and Peter Koidl, "Ultrasensitive femtosecond two-photon detector with resonantly enhanced nonlinear absorption," Opt. Lett. 30, 287-289 (2005)