Coupling of pulsed 0.35-μm laser radiation to aluminum alloys

Abstract

Experiments and theoretical analysis have been performed to investigate the thermal and mechanical coupling of pulsed 0.35-μm laser radiation (τp≊10−6 s) to aluminum targets irradiated in vacuum. Thermal coupling coefficients measured for Al 2024 (as-received and polished) and pure aluminum, and impulse coupling data for polished Al 2024 are presented. We find low fluence (≲5.0 J/cm2) thermal coupling coefficients of 0.4 for as-received Al 2024, 0.2 for polished or laser-cleaned Al 2024, and 0.1 for pure aluminum. Neglecting initial surface layer effects, impulse coupling is shown to result from bulk target vaporization for pulse fluences greater than 10 J/cm2. Measurements are also presented for the plasma formation threshold above aluminum targets irradiated in vacuum at 0.35 μm. An intensity threshold of 6×107 W/cm2 is indicated for a pulse duration of 0.5 μs. The impulse coupling and plasma ignition threshold data are shown to be in good agreement with theoretical model predictions.