Regensburg 2002 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 38: Poster 2

HL 38.28: Poster

Donnerstag, 14. März 2002, 16:30–19:00, Poster A

Angle-Integrated FROG for Characterisation of Ultrashort Laser Pulses — •Birger Seifert and Heinrich Stolz — FB Physik Universität Rostock, 18051 Rostock

Spectral interferometry has proven to be a powerful method for phase sensitive spectroscopy. The precondition is a full characterisation of the reference laser pulses as a complex electric field. For wide energy bandgap semiconductors like GaN excitation requires pulses in the ultraviolet spectral region. The characterisation of this pulses is nontrivial, as it is impossible to use standard SHG-FROG techniques due to the nonexistence of appropriate doubling crystals for fundamental wavelengths below 380 nm. Here we explore the possibility of a SFG-process using a thick BBO-crystal (100 µm). This crystal is too narrowband to cover the full bandwidth of the laser pulses, but has the advantage of increased signal strength. The angle of the nonlinear crystal is varied to increase the effective phase matching bandwidth. For this case we derive an exact expression for the SFG-FROG traces. This shows that the angle-summed signal which was proposed recently [1] as a good approximation to the true FROG trace (for crystals with zero length) is frequency shifted and a linewidth different from the exact FROG trace. The frequency shift turns out to be a good measure for the influence of wavevector-mismatch. We propose a new FROG-algorithm based on an iterative procedure, allowing to characterize both laser fields. [1] P. O’Shea, M. Kimmel, X. Gu, R. Trebino, Opt. Expr. 7, 342 (2000)