title: Ultrasensitive femtosecond two-photon detector with resonantly enhanced nonlinear absorption.
abstract: 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/cm2 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.
authors.affiliation: Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastrasse 21, D-79108 Freiburg, Germany. harald.schneider@iaf.fhg.de
authors.forename: Harald
authors.initials: H
authors.lastname: Schneider
authors.forename: Thomas
authors.initials: T
authors.lastname: Maier
authors.forename: H C
authors.initials: HC
authors.lastname: Liu
authors.forename: Martin
authors.initials: M
authors.lastname: Walther
authors.forename: Peter
authors.initials: P
authors.lastname: Koidl