Direct measurements of compressive and tensile strain during shock breakout by use of subnanosecond x-ray diffraction

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Abstract
Shock waves of order 100 kbar were launched into 50‐μm‐thick single crystals of silicon (111) by irradiation with nanosecond pulses of 1.05‐μm laser light at irradiances in the region of 2×1010 W cm−2. A separate laser beam, synchronous but delayed with respect to the shock‐driving beam, and containing approximately 25 J of 0.53‐μm laser light in a pulse of 1 ns (FWHM), was focused to a tight (<100 μm) spot on a separate titanium target to produce a plasma which was a prolific source of He‐like Ti x rays. The x rays were Bragg diffracted from the rear surface of the shocked crystal and the spectrum recorded on an x‐ray streak camera. Changes in interatomic spacings in a region within several microns of the surface were thus deduced from the resultant shift in Bragg angle with a temporal resolution of 50 ps. Shock waves with compressions of order 6% were observed. We observed the crystal in a state of dynamic tension as the two rarefaction waves met. The results are in good agreement with hydrocode simulations in conjunction with x‐ray diffraction calculations.