RESUMO
Pump and probe reflective imaging using a soft x-ray laser probe was applied to the observation of the early stage of femtosecond laser ablation process on platinum. In strongly excited area, drastic and fast reflectivity drop was observed. In moderately excited area, the decay of the reflectivity is slower than that in the strongly excited area, and the reflectivity reaches its minimum at t = 160 ps. In weakly excited area, laser-induced reflectivity change was not observed. In addition, the point where the reflectivity dip was observed at t = 10 ps and t = 40 ps, coincides with the position of the edge of reflectivity drop at t = 160 ps. These results give the critical information about the femtosecond laser ablation.
RESUMO
We demonstrate the temporal contrast enhancement in a petawatt-class Ti:sapphire chirped-pulse amplification (CPA) laser system. An extra saturable absorber, introduced downstream after a low-gain optical parametric chirped-pulse amplification (OPCPA) preamplifier, has improved the temporal contrast in the system to 1.4×10(12) on the subnanosecond time scale at 70 TW power level. We have achieved 28 J of uncompressed broadband output energy with this system, indicating the potential for reaching peak powers near 600 TW.
RESUMO
The results of Monte Carlo calculated dose distributions of proton treatment of ocular melanoma are presented. An efficient spot scanning method utilizing active energy modulation, which also minimizes the number of target spots was developed. We simulated various parameter values for the particle energy spread and the pencil beam diameter in order to determine values suitable for medical treatment. We found that a 2.5-mm-diameter proton beam with a 5% Gaussian energy spread was suitable for treatment of ocular melanoma while preserving vision for the typical case that we simulated. The energy spectra and the required proton current were also calculated and are reported. The results are intended to serve as a guideline for a new class of low-cost, compact accelerators.