Characteristics of hard x-ray emission from laser-induced vacuum spark discharges

An experimental study of the characteristics of hard x-ray emission in laser-induced vacuum spark discharges has been carried out. The spark discharge is performed in a gap (10 mm) of pin electrodes using a Marx generator and a laser pulse to produce Au plasma on the tip of an anode. When spark discharge with charge voltage of 150 kV occurred simultaneously with the incidence of a laser pulse, an x-ray pulse made of a short (∼20 ns) x-ray spike pulse and a long (∼400 ns) pulse was emitted with high intensity (∼10 mR per shot). The two pulses appeared at the beginning and at the latter part of discharge. The effective photon energy was around 150 and 80 keV, respectively. The results show that the x-ray intensity strongly depends on the timing of the onset of the discharge with respect to the laser irradiation, the laser intensity, and the charge voltage. The mechanisms responsible for the x-ray emission are discussed in terms of the results observed