Abstract

We report on experiments carried out at high intensities with a table top terawatt laser system which employs the chirped pulse amplification technique [1]. High efficiency frequency doubling (85% conversion from 1 pm to 0.53 pm wavelength) is used to generate high contrast pulses. The green beam (1 J in 300 fs pulse with no prepulse) is focused to intensities up to 5 × 10¹⁸ W/cm². At these intensities relativistic effects and ponderomotive pressure [2] are important issues for the interaction. The interaction of a very clean pulse with solid matter allows the production of hot solid density plasmas which offers a unique way to address experimentally, in the laboratory, some problems of great astrophysical interest [3] and of importance for atomic physics. In order to get fully ionized solid density emitting matter, a careful optimisation of the interaction regime is required [4]. On one hand laser intensity must be high enough to overcome, with radiation pressure, the thermal and hydrodynamic mechanisms tending to spread the plasma at low intensity. On the other hand the intensity must be kept below some limit above which we enter the regime of cratering and hole boring problems associated with ultra-high radiation pressures [5], We present and discuss such an optimisation study for the generation of Li-like solid density plasmas. The plasma density and temperature are deduced from line broadening [6] and line ratio calculations (using TRANSPEC code). We observe an optimum at a laser intensity of 10¹⁸ W/cm² for the generation of Al plasmas radiating Li-like emission at solid density. We will discuss the physics of the various interaction regimes for laser intensities between 10¹⁷ W/cm² and 10¹⁹ W/cm² and for various Z material. The implications of these results for the design of an ultra-fast X-ray sources [7] will be outlined.

© 1994 Optical Society of America