Quadratic detection and autocorrelation measurements with two-photon quantum well infrared photodetectors


Quadratic detection and autocorrelation measurements with two-photon quantum well infrared photodetectors

Schneider, H.; Winnerl, S.; Liu, H. C.; Drachenko, O.; Helm, M.; Walther, M.; Faist, J.

The two-photon quantum well infrared photodetector (QWIP) comprises three equidistant subbands, two of which are bound in the quantum well, and the third state in the continuum. This results in a resonantly enhanced optical nonlinearity, which is by six orders of magnitude stronger than in usual semiconductors. In addition, temporal resolution is only limited by the sub-ps intrinsic time constants of the quantum wells, namely the intersubband relaxation time and the dephasing time of the intersubband polarization. Both properties make this device very promising for quadratic autocorrelation measurements of pulsed mid-infrared sources, including modelocked quantum cascade lasers, radiation obtained by nonlinear optical frequency conversion, and free-electron lasers (FEL).
We have performed autocorrelation measurements of ps optical pulses from the free-electron laser (FEL) facility FELBE at the Forschungszentrum Rossendorf. Using a rapid-scan autocorrelation scheme at a scan frequency of 20 Hz, high-quality quadratic autocorrelation traces are obtained, yielding ratios close to the theoretically expected value of 8:1 between zero delay and large delay for interferometric autocorrelation, and 3:1 for intensity autocorrelation. Thus, two-photon QWIPs provide an excellent new approach to online pulse monitoring of the FEL. In addition, we have investigated the saturation mechanism of the photocurrent signal, which is due to internal space charges generated in the detector. We will also report on room temperature operation of two-photon QWIPs.

Keywords: quantum well infrared photodetector; two-photon absorption; intersubband transition; quadratic autocorrelation; GaAs/AlGaAs

  • Lecture (Conference)
    9th International Conference on Mid-Infrared Optoelectronics: Materials and Devices (MIOMD-IX), 07.-11.09.2008, Freiburg, Deutschland

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Publ.-Id: 11702