Interferometric study of laser-produced plasmas

Abstract

High‐quality interferograms of laser‐produced plasmas with spatial resolution of 15 μm are obtained using a relatively simple Jamin‐type interferometer and a precisely timed 30‐psec probing laser pulse from a mode‐locked Nd : YAG laser, frequency doubled to 532 nm. The spatial resolution attainable with the present arrangement is limited by the velocity of the expanding plasma and the finite duratiaon of the probing pulse. The plasmas are produced by focusing a Nd : glass Q‐switched laser pulse (0.5 GW, 10¹¹–10¹³ W cm⁻²) onto slab targets of Al, Mg, and (CH₂)_n. The electron density distribution, plasma dimension, and expansion velocity for both point and line foci are studied as a function of time delay between the mode‐locked and Q‐switched laser pulses. The results obtained with different durations of the heating (Q‐switched) pulse and with the various target material are compared.