Dynamics of thin metal foils irradiated by moderate-contrast high-intensity laser beams

Laser contrast is a crucial parameter in experiments with high-intensity high-energy pulses. For relativistic intensities of the main pulse greater than or similar to 10(19) W/cm(2), even high-contrast beams can produce plasma on the target surface due to a long nanosecond prepulse action which results in an undesirable early smearing of the target. In particular, dynamics of thin foils under the prepulse action is especially important for the laser ion acceleration technique and x-rays generation. To avoid the influence of the long laser prepulse, a thin foil can be arranged in front of the target. The analysis of the multi-stage foil dynamics is performed using a wide-range two-temperature hydrodynamic model, which correctly describes the foil expansion starting from the normal solid density at room temperature. Simulations show that varying the foil thickness, one can diminish the prepulse transmission through the foil material in many orders of magnitude and at the same time provide the total transparency of the foil plasma by the moment of the main high-intensity ultra-short pulse arrival. Modeling of shielded and unshielded target dynamics demonstrates the effectiveness of this technique. However, the prepulse energy re-emission by the shielding foil plasma can be sizable producing an undesirable early heating of the target placed behind the foil. (C) 2012 American Institute of Physics. [doi:10.1063/1.3683687]