Berlin 2001 – wissenschaftliches Programm

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P: Plasmaphysik

P 3: Dense Plasmas

P 3.6: Vortrag

Dienstag, 3. April 2001, 17:55–18:10, 2053

High Order Harmonics from Solid Surfaces: Role of Plasma Mirror Distortions — •Alexander Tarasevitch, Clemens Dietrich, and Dietrich von der Linde — Institut für Laser und Plasmaphysik, Universität Essen, 45117 Essen, Germany

The generation of high order harmonics from solid surfaces can be explained as a result of reflection from the effective No-dqplasma mirrorNo-dq oscillating in the strong field of the incident wave. The use of femtosecond laser pulses naturally leads to the formation of such a mirror because on this time scale the steep gradient of the plasma density is maintained. However, laser pulses with high contrast ratio and steep leading edges are essential. Moreover, possible distortions of the plasma mirror under high-intensity pumping should be also taken into account.

With the pump intensities up to 10¹⁸ W/cm² we observe nearly diffraction limited high order harmonic emission from solid targets. Pulses with the duration of 120 fs and the contrast ratio of 10⁵ at 1 ps are used. Conversion efficiencies up to 10⁻⁶ (tenth harmonic) are achieved. With the help of a new interferometer schematic we observe a spatially resolved structure of the plasma mirror and its evolution. A controllable prepulse is used to generate plasma in order to establish a plasma scale length of the desired value. The plasma surface distortions grow and the efficiency of harmonic generation rapidly drops with increasing of the plasma scale length.