Upgrade of the nhelix laser system at GSI

The first high energy laser system that became operational at GSI is the ”nanosecond high energy laser for heavy ion experiments” (nhelix). This system has recently been improved significantly. Due to major changes in the system layout, the quality in terms of temporal and spatial beam homogeneity was improved, while at the same time the output energy was raised up to 120 J. This could be achieved with the available number of amplifiers, which significantly brought down the cost for the upgrade. Moreover, a second front-end with shorter pulse length was integrated into the laser amplifier chain. Therefore the nhelix system is now capable of delivering one beam with 120 J in 14 ns (ns-beam), while the second beam line is still under construction and is supposed to provide 5 J in 0.5 ns (sub ns-beam). While the power level of these two beams is of the same order of magnitude, their application at the plasma physics experiments is different. The high energy pulse with rather long pulse duration is primarily used to generate a high density plasma from thin solid state targets, while the second beam with short pulse length in comparison to the heating pulse and the timescale on which the hydrodynamic expansion of the plasma takes place, serves as a diagnostic tool. This more complex and versatile setup enables a great variety of experiments in the field of plasma physics, especially in combination with the PHELIX laser (Petawatt High Energy Laser for heavy Ion eXperiments), which is expected to deliver first light on the kJ level to the experimental area by the end of 2005 [1]. The actual laser configuration is one of the MOPA type (master oscillator-pulsed amplifier). A master oscillator (Nd:YAG) generates a low energy pulse for amplification, that is followed by rod amplifiers (silicate-glass), whose diameter increase stepwise up to 64 mm for the last amplifier. As the laser light fluence is well below the saturation level, the same amplifier can be used multiple times to increase the energy of a beam, e.g. in a double pass configuration, or one can even use the same amplifier to gain energy for pulses coming from different oscillators. The latter configuration has been realized with the first two amplifiers; see