Plasma x-ray emission produced by ruby lasers at 1012 W/cm2

Abstract

Q‐switched 20‐nsec ruby‐laser pulses (∼0.5 GW) were focused to about 10¹² W/cm² on targets containing elements in the range 6⩽Z⩽68. Time‐ and space‐integrated x‐ray emission from plasmas 200 μm in diameter with lifetimes near 12 nsec was measured with four active detectors at energies between 0.1 and 5 keV. Maxima in x‐ray intensity measured by each detector occurred when binding energies of core electrons in target atoms were 20–30 times the electron plasma temperature. Calculated detector response functions together with coronal‐model plasma emission computations were used to analyze the atomic‐number dependence of the detector signals. A plasma electron temperature of 70 eV and an electron density of about 4×10²⁰ cm⁻³ gave the best fit to the ratios of signals. Computed spectra for this temperature showed that the peaks in the low‐energy detector (an x‐ray diode most sensitive near 0.15 keV) were due in part to line radiation. Peaks in the three detectors sensitive above 1 keV (two silicon PIN diodes and an ionization chamber) were primarily due to recombination radiation. The results of this work augment an earlier similar, but limited, study at 10¹² W/cm².