Soft x-ray spectra produced by subpicosecond laser-double-pulses

Abstract

Soft x-ray spectra generated on flat Al targets by a 500 fs KrF* laser pulse (intensity 5.3×1015 W/cm2), preceded by a prepulse of the same pulse duration, have been measured as a function of the pulse separation and the prepulse intensity. It was found that not only the total x-ray emission was much stronger when the prepulse was present but, in particular, lines in the shorter wavelength region had a higher intensity than without prepulse, and were strongly dependent on the time separation between the prepulse and the main pulse.

Angle-dependent x-ray emission and resonance absorption in a laser-produced plasma generated by a high intensity ultrashort pulse

“…[19], the plasma scale length L =n e /\n e (n e is the electron density in the vicinity of the critical density) and the plasma expansion velocity c s are estimated to L ^ 50 nm ^ 0.2A, and c s ~ 10 7 cm/s. These values are in good agreement with other experiments for similar laser and plasma conditions [7,8,20].…”

“…Several experimental investigations that study the interaction of laser radiation with such plasmas for intensities up to -10 16 Wcm ~2 have been reported [1][2][3]. The observation of x rays emitted from plasmas produced by ultrashort laser pulses has led to a number of very interesting results [4][5][6][7][8][9]. For example, the emission of spontaneous x rays up to energies exceeding 1 MeV has been observed [9].…”

“…The spectra of the emitted x rays were measured by a grazing incidence spectrometer in the wavelength range between 25 A ( -500 eV) and 250 A ( -50 eV) [8]. The spectrum was dominated by a broad continuum that extended beyond the short wavelength cutoff of the spectrometer.…”

Characterization of the spatiotemporal evolution of laser-generated plasmas

“…Those experiments probed medium density plasmas ͑10 18 / cm 3 ͒ using x-ray emission and optical Thomson scattering to characterize electron temperatures and showed qualitative, but limited quantitative, agreement with models. Novel double pulse techniques 11 have also used soft x-ray emission from laserablated metals to probe the spatiotemporal dynamics of such plasmas. 12 Such measurements are complicated by the self absorption of the soft x rays and have shown similarly limited quantitative agreement with theory.…”

Strongly enhanced soft x-ray emission at 8 nm from plasma on a neodymium-doped glass surface heated by femtosecond laser pulses

“…One possible way to increase absorption is the use of a prepulse which forms a gaseous plasma before the incidence of an intense main pulse. [3][4][5][6][7][8] We have observed an enhancement of 100 times in soft x-ray emission using this scheme. 6,8,9 The low-density plasma created by the prepulse not only increased the light absorption, but also broadened the pulse duration in the soft x-ray region to more than 100 ps.…”