Reflection of XeCl laser radiation from an aluminum target in the presence of an erosion plasma

An experimental investigation was made of the processes of interaction of radiation from an XeCl excimer laser (λ = 308 nm, τ = 20 ns) with aluminum. The threshold of formation of an erosion plasma in vacuum (q _* = 200 MW/cm²) was independent of the number N of the pulses. The threshold q _* in air depended strongly on N and could fall to 70 MW/cm², due to the formation of a strongly absorbing layer on the target surface. The depth of the layer removed by radiation of intensity q ≈ 1 GW/cm² could reach 1 μm per pulse. The average optical thickness of a plasma created by one pulse was of the order of 0.3 at λ = 308 nm. Evaporation by XeCl laser radiation increased the aluminum absorptivity by a factor of 3–5. The erosion plasma temperature did not exceed 2 eV for q ≈ 1 GW/cm². A general energy balance was determined for the laser radiation–target–plasma in vacuum.