Experiments on Nike KrF Laser Advance Basic Understanding of Impulsively Shocked Matter at High Pressures
Two experiments on the Nike krypton fluoride laser explored the interactions of high pressure shocks with targets that had imposed sinusoidal ripples on their surface. Both experiments utilized laser beams to generate high pressure shocks and both utilized laser generated x rays to probe interactions of the shocks with the target.
Top: experimental (solid line) and simulated (dotted line) time histories of the areal mass modulation of 45 μm wavelength in a 125 μm thick target. Bottom: areal mass perturbations obtained from the streak image of an x-ray backlit target
a) Jet formation on rear surface with lower pressure shocks. (35-J 4-ns laser pulse) Image is 14 ns after application of shock. b) Transition from jet formation to feed-out oscillations (no jets) at intermediate pressure. (105 J 4-ns laser pulse). Jets still occur at the edges of the laser illumination. c) Feed-out oscillations developed by 1250 J laser pulse. Picture, taken with a double pulse x-ray backlighter to show temporal evolution.
Experiment with impulsively driven targets:
By utilizing short laser pulses, shocks were applied to the target where the applied pressure was shorter than the shock transit time. X-ray backlit images measured the evolution of the areal mass non-uniformity. The results are in good agreement with predictions by NRL’s FASTRAD3D radiation-hydrocode.
Experiment showing transition to jet formation:
Jets are observed in side-on images of targets where targets are shocked by Nike beams with reduced intensity.