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Proceedings Paper

Autocorrelation measurements of the FELBE free-electron laser and photocurrent saturation study in two-photon QWIPs
Author(s): H. Schneider; O. Drachenko; S. Winnerl; M. Helm; M. Walther
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Paper Abstract

The two-photon QWIP approach involves three equidistant subbands, two of which are bound in the quantum well, and the third state is located in the continuum. The intermediate subband induces a resonantly enhanced optical nonlinearity, which is about six orders of magnitude stronger than in usual semiconductors. 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 pulse diagnostics of pulsed midinfrared lasers. We have performed autocorrelation measurements of ps optical pulses from the free-electron laser (FEL) facility FELBE at the Forschungszentrum Dresden 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 technique for 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.

Paper Details

Date Published: 8 February 2007
PDF: 9 pages
Proc. SPIE 6471, Ultrafast Phenomena in Semiconductors and Nanostructure Materials XI and Semiconductor Photodetectors IV, 64710T (8 February 2007); doi: 10.1117/12.701895
Show Author Affiliations
H. Schneider, Forschungszentrum Dresden Rossendorf (Germany)
O. Drachenko, Forschungszentrum Dresden Rossendorf (Germany)
S. Winnerl, Forschungszentrum Dresden Rossendorf (Germany)
M. Helm, Forschungszentrum Dresden Rossendorf (Germany)
M. Walther, Fraunhofer-Institute for Applied Solid State Physics (Germany)


Published in SPIE Proceedings Vol. 6471:
Ultrafast Phenomena in Semiconductors and Nanostructure Materials XI and Semiconductor Photodetectors IV
Marshall J. Cohen; Kong-Thon Tsen; Joseph P. Estrera; Jin-Joo Song, Editor(s)

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