Dresden 2011 – scientific programme

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MO: Fachverband Molekülphysik

MO 18: Experimental Techniques and Various Topics

MO 18.1: Talk

Wednesday, March 16, 2011, 16:30–16:45, MER 02

Two-photon absorption as convenient method for the online autocorrelation measurement of sub 20-fs pulses in the deep UV — •Nils Krebs, Christian Homann, Peter Lang, and Eberhard Riedle — Lehrstuhl für BioMolekulare Optik, LMU München

We show that two-photon absorption (TPA) in thin crystals and glas disks is a convenient and easy to handle method for the characterization of ultrashort pulses in the UV. We create two replicas of the pulse by reflection off an uncoated fused silica cover slip and chirp compensation by a second cover slip and focus them in e.g., a BBO crystal chosen for its high TPA coefficient. At temporal overlap, the probe pulse is depleted by the strong pump pulse through TPA to create the autocorrelation signal. In contrast to the widely used intensity autocorrelation by frequency doubling, TPA is not hampered by the need for phasematching and can therefore be used down to the deep UV. With the proper choice of material we can cover a wavelength range from 200 nm up to the visible. By referencing to the laser fluctuations we achieve an excellent signal to noise ratio that allows for the online measurement of pulses with energies down to a few nJ at 1 kHz repetition rate. The frequency doubled output of a noncollinear optical parametric amplifier is measured down to pulse durations well below 20 fs and crosscorrelations of UV pulses as short as 35 fs are demonstrated. Due to the compact design the autocorrelator can easily be incorporated in exisiting pump-probe setups and be used for the online optimization of the pulse duration at the sample position.