Radiative Losses of Plasma on Interaction of Ultrashort Laser Pulses with Matter

Radiative losses of plasma produced by ultrashort laser pulses near the surface of solid targets were studied by the methods of high‐resolution x‐ray spectroscopy and using the numerical simulation of gas‐dynamics and radiation processes. The experiments were carried out at the “NEODIM” laser facility in the Central Research Institute for Machine Building. The flux density was as high as 1017 W/cm2 when the radiation was focussed onto the surface of solid targets from Al and Cu. The time‐integrated discrete spectra of plasma of the multiply charged ions were recorded in the soft x‐ray band from 0.8 to 3.0 keV. The experimental spectra were compared with the results of numerical calculations within the framework of the model, which considered both hydrodynamic and radiation‐collisional processes. The association of the radiation dynamics of the individual groups of lines with the spatial and temporal dynamics of the laser torch was revealed. Such an association permits one to judge the nonstationary processes in the expanding plasma even by the spectra integrated over time. From comparison of the experimental results and model calculations, it follows that the line emission of a relatively narrow (in the charge number) group of ions constitutes the major portion of radiation losses.