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.