Characteristics of lateral and axial transport in laser irradiations of layered-disk targets at 1.06 and 0.35 μm wavelengths

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Abstract
Results and analysis are presented for Be‐on‐Al disk target irradiations at 1.06 and 0.35 μm laser wavelengths with 600–700 psec pulses, 240 μm spot diameter, and 1×1014 W/cm2 absorbed intensity. Absorptions of 32%–39% (1.06 μm) and 90% (0.35 μm) are largely due to inverse bremsstrahlung. The hard x‐ray spectra indicate low hot‐electron fractions of 10−2 (1.06 μm) and 10−4 (0.35 μm). Backreflected light shows strong hot spots for 0.35 μm irradiations. Multiple absolute and relative x‐ray measurements are compared with one‐ and two‐dimensional computer hydrodynamics calculations. Only weak indications of lateral transport are found and limits are set from x‐ray imaging and spectral data from targets with and without a surrounding Ti shield. Axial transport appears strongly inhibited at 1.06 μm and mildly inhibited at 0.35 μm wavelength. Measured shock‐wave transit times and velocities imply ablation pressures of 7 Mbar (1.06 μm) and 11 Mbar (0.35 μm).