A comparative study of the inner-shell and the ionic line radiation from ultra-short laser-produced magnesium plasma

Abstract

The inner-shell radiation (K-α) and the ionic line radiation (He-α) from magnesium plasma, generated by the interaction of a 3 TW, 45 fs laser, have been studied simultaneously using an x-ray crystal spectrograph. The effect of the variation of the laser intensity and its offset from the best focus position has been studied. He-α and K-α x-ray yields are found to scale with the laser intensity as IL1.5 and IL0.6 respectively. The K-α x-ray conversion shows a maximum at the best focus and reduces symmetrically on either side of the best focus position, whereas the He-α conversion peaks when the target is placed before the focused laser beam. The angular distribution for the He-α as well as the K-α emissions shows a maximum in the forward direction and the intensity reduces with the increase in angle θ with respect to the target normal as cosα θ. The value of α is 0.7 and 3 for He-α and K-α respectively. The experimentally observed variation of the He-α line conversion for different laser parameters has been explained by considering the change in preformed plasma conditions, and the variation in the K-α emission has been explained by considering hot electron generation and their propagation in the bulk solid target. The plasma conditions prevalent during the emission of the x-ray spectrum were identified by comparing the experimental spectra with the synthetic spectra generated using the spectroscopic analysis code PrismSPECT. The results will be useful in designing laser-produced plasma x-ray line radiation sources of photon energy in the range of 1–2 keV, for its potential use as a probe pulse in x-ray backlighting, or time-resolved x-ray diffraction studies.

Emerging trends in X-ray spectroscopic studies of plasma produced by intense laser beams

“…A fit for ionic line emission with temperature T = 130 eV, and e 20 ×10 cm , T = 50 keV and the hot e hot electron fraction = 0.01 was obtained. A spatially and temporally averaged value of the electron temperature of ~100 -200 eV and a hot electron fraction of ~ 0.01 is expected in our experimental conditions[12]. The electron density value which fits the spectra is close to the turning point 20 -3 o density (~ 7.8 ×10 cm ) for a 45 obliquely incident 800 nm Ti:sapphire laser beam.…”

“…X-ray spectroscopy of dense plasma produced by high intensity ultra-short laser provides information for the basic research and optimization of plasma parameters for controlling x-ray source properties for applications. We studied the keV x-ray emission spectrum ( Figure T pulses, focussed at an intensity of 4 x 10 W cm [12]. It has well defined ionic x-ray line features corresponding to high temperature plasma, as well as characteristic K-á emission from cold atom and lower charge ions.…”