Theory for laser simulation of hypervelocity impact

A theory is developed to determine the parameters for simulation of the hypervelocity impact of small particles on a surface by focusing a high power pulsed laser upon that surface. It is proposed that the early time history of hypervelocity impact effects can be simulated by requiring that the laser induced surface pressure equal the surface impact pressure, equating the laser pulse time to a particle/surface interaction time, and setting the focal spot diameter equal to the particle diameter. Calculations of impact pressure versus projectile velocity are performed using an idealized one dimensional model for shock wave propagation. A simplified theory for the interaction of a highly focused pulsed laser beam with a surface is developed to obtain the laser induced surface pressure. Results of a sample calculation for water droplets impacting a graphite surface between 3 and 6 km/sec indicate that laser intensities of 5×10¹⁰–5×10¹¹ W/cm² are required. The corresponding laser energies are strongly particle size and shape dependent and range from 0.01 J with a 5 nsec pulse time for 20 μ radius particles to 2 J with a 20 nsec pulse time for 80 μ radius particles. A qualitative comparison of data for high power laser produced craters and hypervelocity impact produced craters is also presented.