Simulations of a photopumped X-ray laser using the H-like Cl-Li-like Se scheme

Calculations of the modal photon densities and gain in a photopumped Cl XVII-Se XXXII X-ray laser are presented. In this paper we undertake a realistic simulation of the generation of both Cl and Se plasmas, using a high-power optical laser, which includes radiation from both Ly-α fine-structure components of H-like Cl pumping the 2p3/2-5d5/2 transition in Li-like Se. The calculations are performed in two dimensions in a realistic geometry taking into account plasma gradients. This gives information about the spatial extent and time evolution of X-ray lasing gain on the 5-4 transitions (39.5 Å) in Li-like Se. We find that gain (about 200 cm-1) is expected only when the optical laser includes a pre-pulse. Calculations show that the absorption of pumping radiation in the pumped plasma can reduce the gain by 20%. Time-dependent calculations have shown that the gain is reduced by 30% in comparison to the steady-state calculations. The effect of the spectral profile and self-radiation of 5d5/2-2p3/2 transition in Li-like Se reduces the gain by about 2%. © 2003 Elsevier Ltd. All rights reserved

K-shell spectroscopy of an independently diagnosed uniaxially expanding laser-produced aluminum plasma

We present detailed spectroscopic analysis of the primary K-shell emission lines from a uniaxially expanding laser-produced hydrogenic and heliumlike aluminum plasma. The spectroscopic measurements are found to be consistent with time-dependent hydrodynamic properties of the plasma, measured using Thomson scattering and shadowgraphy. The K-shell population kinetics code FLY with the measured hydrodynamic parameters is used to generate spectra that are compared to the experimental spectra. Excellent agreement is found between the measured and calculated spectra for a variety of experimental target widths employed to produce plasmas with different optical depths. The peak emission from the hydrogenic Lyman series is determined to be from a temporal and spatial region where the hydrodynamic parameters are essentially constant. This allows a single steady-state solution of FLY to be used to deduce the electron temperature and density, from the measured line ratios and linewidths, for comparison with the Thomson and shadowgraphy data. These measurements are found to agree well with time-dependent calculations, and provide further validation for the FLY calculations of the ionization and excitation balance for a K-shell aluminum plasma. We also discuss the possible application of this data as a benchmark for hydrodynamic simulations and ionization/excitation balance calculations

Measurements of the XUV mass absorption coefficient of an overdense liquid metal

The increase in the XUV mass absorption coefficient of liquid aluminium, produced by high-power-laser shock-compression, is measured using XUV laser radiography. At a photon energy of 63 eV a change in the mass absorption coefficient by up to a factor of ∼2.2 is determined at densities close to twice that of solid and electron temperatures of the order of 1 eV. Comparison with hydrodynamic simulations indicate that the absorption coefficient scales with density as ρ1.3±0.2

Gain dynamics in a soft-X-ray laser amplifier perturbed by a strong injected X-ray field

International audienceSeeding soft-X-ray plasma amplifiers with high harmonics has been demonstrated to generate high-brightness soft-X-ray laser pulses with full spatial and temporal coherence. The interaction between the injected coherent field and the swept-gain medium has been modelled. However, no experiment has been conducted to probe the gain dynamics when perturbed by a strong external seed field. Here, we report the first X-ray pump–X-ray probe measurement of the nonlinear response of a plasma amplifier perturbed by a strong soft-X-ray ultra-short pulse. We injected a sequence of two time-delayed high-harmonic pulses (λ = 18.9 nm) into a collisionally excited nickel-like molybdenum plasma to measure with femtosecond resolution the gain depletion induced by the saturated amplification of the high-harmonic pump and its subsequent recovery. The measured fast gain recovery in 1.5–1.75 ps confirms the possibility to generate ultra-intense, fully phase-coherent soft-X-ray lasers by chirped pulse amplification in plasma amplifiers