ABSTRACT
The harmonic emission from thin solid carbon and aluminum foils, irradiated by 150 fs long frequency-doubled Ti:sapphire laser pulses at lambda=395 nm and peak intensities of a few 10(18) W/cm(2), has been studied. In addition to the harmonics emitted from the front side in the specular direction, we observe harmonics up to the 10th order, including the fundamental from the rear side in the direction of the incident beam, while the foil is still strongly overdense. The experimental observations are well reproduced by particle-in-cell simulations. They reveal that strong coupling between the laser-irradiated side and the rear side occurs via the nonlocal electron current driven by the laser light.
ABSTRACT
Absorption of L-M and L-N transitions of nickel has been measured using point projection spectroscopy. The x-ray radiation from laser-irradiated gold cavities was used to heat volumetrically nickel foils "tamped with carbon" up to 20 eV. Experimental spectra have been analyzed with calculations based on the spin-orbit split arrays statistical approach and performed for each ionic species Ni5+ to Ni11+. Using a least-squares fit, this method provides an ion distribution broader than at local thermodynamic equilibrium, which is explained by spatial and temporal temperature gradients. A major improvement in the simulation of the absolute value of transmission is obtained with a resolved transition array statistical calculation that reproduces the experimental spectrum with the nominal areal mass density by taking into account the saturation of narrow lines.
ABSTRACT
We present time-resolved x-ray spectra of C, F, Na, and Al, generated by focusing ultrashort frequency doubled Ti:sapphire laser pulses on solid plane targets. Using a high resolution x-ray streak camera in combination with a laser triggered accumulation system, we achieved a time resolution of 1.7 ps when adding the x-ray signal of many thousands of laser shots. K-shell resonance line emission with a duration in the range of 2-4 ps is observed. Ly alpha emission is generally observed to be faster than He alpha emission and the x-ray pulse duration is observed to decrease with increasing atomic number. A hydrodynamic code in combination with an atomic kinetics code is applied for simulation of time-resolved plasma emission, showing good agreement with experimental data.