Laser-Generated Plasmas

Summary form only given. Hot plasmas can be generated by fast and intense laser pulses ablating solids placed in vacuum. A Nd:YAG laser, operating at fundamental and second harmonic, emitting 9 ns pulses with a maximum energy of 900 mJ, focused on metallic surfaces, produces high ablation yields, of the order of mug/pulse, and dense plasmas which expands adiabatically and at supersonic velocity along the normal to the target surface. Plasma emits neutral and charged particles. Charge states up to 10+ have been measured in heavy elements ablated with intensities of the order of 10¹⁰ W/cm². The ion temperature of the plasma has been measured through the ion energy distributions measured with a special ion energy analyser. The electron temperature is measured through Faraday cups placed at the end of long drift tubes by using time-of-flight technique. The neutral temperature is measured with a special mass quadrupole spectrometer placed along the normal to the target surface. The plasma temperature increases with the laser pulse intensity. The ion temperature reaches values of the order of 400 eV; the electron temperature is of the order of 0.1 eV and the neutral temperature is of the order of 200 eV. The experimental apparatus, the diagnostic techniques and the procedures for the plasma temperature characterization will be presented and discussed in detail