Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Two-photon quantum well infrared photodetectors (QWIPs) are based on three equidistant subbands, two of which are bound in the quantum well, and the third one in the continuum. This configuration leads to a resonantly enhanced optical nonlinearity, which is by six orders of magnitude stronger than in bulk semiconductors [1]. This device is useful 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). In quadratic autocorrelation experiments, temporal resolution of two-photon QWIPs is only limited by the sub-ps intrinsic time constants of the intersubband transitions, namely the intersubband relaxation time and the phase relaxation time.
We will report on autocorrelation measurements at various wavelengths from the mid-infrared to the Terahertz regimes using ps optical pulses from the FEL at the Forschungszentrum Dresden Rossendorf. In particular, quadratic detection at wavelengths around 5.5 µm is still possible at room temperature [2], which is crucial for applications in practical systems. Two-photon detection beyond the Reststrahlen band will also be addressed.
[1] H. Schneider, T. Maier, H. C. Liu, M. Walther, and P. Koidl, Optics Lett. 30, 287 (2005).
[2] H. Schneider, H. C. Liu, S. Winnerl, O. Drachenko, M. Helm, J. Faist, App. Phys. Lett. 93, 101114 (2008).