Dresden 2011 – scientific programme

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A: Fachverband Atomphysik

A 28: Attosecond physics II

A 28.3: Talk

Wednesday, March 16, 2011, 11:15–11:30, BAR 205

Time-resolved phase matching and macroscopic gating in few-cycle high-harmonic generation: Simulation and experimental results — •Michael Schönwald, Christian Ott, Philipp Raith, and Thomas Pfeifer — Max-Planck-Institut für Kernphysik, Heidelberg, Deutschland

High-harmonic generation (HHG) is a key technology for the direct exploration of atomic and molecular electron dynamics. This process is based on a macroscopically coherent response of a medium, i.e. the radiation produced by multiple atoms has to be phase matched. A time-domain simulation of phase matching will be presented, showing how phase matching can act as a temporal gate and thus allow HHG only during the leading edge of the driving laser pulse. The behaviour of the leading-edge gating mechanism will be analysed for different experimental conditions, such as peak intensity of the driving laser pulse, density of the gaseous generation medium and the distance between focus and generation medium. In our experiments, the leading-edge gate is observed by carrier-envelope phase (CEP) dependent measurements of HHG, including analysis of the half-cycle cut-off (HCO) emission. Experiments are carried out for various pressures and compared to the simulation. The HCO photon energy allows to extract the field strength of an individual half cycle of the driving laser pulse. In addition, the pressure-dependent total harmonic yield measured in the experiment is compared to the simulation for the leading-edge regime and yields a qualitative agreement, further confirming our understanding of the process that allows to generate isolated attosecond pulses.