Production of hot electrons by two-plasmon decay instability in uv laser plasmas

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Abstract
Hot electron emission from a uv laser produced plasma with incident intensities 8×1013–2×1015 W/cm2 was measured by means of an electron spectrometer. Because of the small hot electron population, the self-consistent target potential due to escaped electrons may be considered for the first time in the data reduction. The total energy in hot electrons of temperature 50 keV is shown to be ≲10−3 of the incident laser energy. The target potential ≲80 kV. The hot electron temperature is essentially independent of intensity, the angular distribution of electron emission shows a weak polarization asymmetry, and the intensity threshold of hot electron production is 5×1013 W/cm2, all consistent with the two-plasmon decay instability being responsible for heating the electrons. The predicted spectrum of plasma waves is such that the accelerated electrons should be directed into the plasma almost parallel to the laser axis. Because only a small fraction of these electrons are reflected backwards to the detector, the x-ray yield is a factor of 20 higher than the escaped electrons would indicate.