Production of Energetic Highly Ionized Plasma by Laser Irradiation of Lithium Hydride Pellets

Spherical LiH pellets have been utilized as targets for high-power, fast-rising, nanosecond laser pulses. Using different pulse lengths, τ, it has been shown that the pellets behave as a continuous source of energetic plasma during a time tl (called “interaction time”) depending on the pellet size and on the laser flux density. For pellets 50μ in diameter and flux densities of 1.5 × 1012W/cm2, tl is 20 nsec; the degree of ionization approaches 100% (about 1016 ions in the plasma) and the root-mean-square expansion velocity is 107 cm/sec; the total plasma energy is about 0.5 J with an energy transfer efficiency of 10%. The general behavior of the burning process agrees with the extension to small pellets of the theoretical model developed for the case of massive targets.