Reflection of ultra-intense picosecond light pulse from metal target.

The dependence of specular reflectivity of a picosecond ligh pulse from a metal (Cu) target - placed perpendicularly to direction of incident light -on the light intensity in the intensity range 3x10 14 - 3x10 16 W/cm is investigated experimentally. It has been found that , contrary to the experiments with high-contrast femtosecond pulses, the reflectivity decreases as light intensity increases to the value ~7x10 15 W/cm2, and above this intensity the value of the reflectivity is provided, assuming that the interaction of the main picosecond pulse with the target is modifield by a short-lasting (<1 ns) prepulse producing an expanding preplasma on the target surface.