Focusing the beam of a compact, repetitively pulsed x-ray laser to study the interaction of radiation with metallic targets and x-ray reflectometry

The interaction of focused soft x-ray laser radiation with metallic targets was studied experimentally. The radiation of a capillary-discharge Ne-like Ar ion laser (λ=46.9 nm) with a repetition rate of 1 Hz was focused on the surface of metallic samples by using a spherical Si/Sc multilayer mirror. The radiation intensity at the target surface was far greater than the threshold for laser ablation of the materials in use — aluminium, brass, and stainless steel. A study of the shape of laser craters in relation to the position of the caustic of the focusing mirror, combined with computer ray-tracing simulations, made it possible to determine the radiation intensity distribution in the focal region of the mirror. The radiation energy density in the 2-μm central domain of the focal spot was 10² J/cm^-2, and the corresponding intensity was 10¹¹ W/cm^-2. The reflectivity of a Si/Sc multilayer mirror was measured as a function of the angle of incidence of the radiation.