| Popis: |
This thesis presents measurements of the production of hot electrons during laser interactions in the irradiance range 10^{16} -10^{20} W cm^{−2}. This intensity regime is accessible with modest ultra-short lasers at ∼ 10^{16} Wcm^{−2} where resonance absorption dominates the electron acceleration. At the higher irradiances (10^{18} -10^{20} W cm^{−2}), petawatt class lasers are required where J × B electron accelera- tion occurs. Fast electron generation using the VULCAN Petawatt laser (irradiances ∼ 10^{20} W cm^{−2}) and the LASERIX facility (irradiances ∼ 10^{16} W cm^{−2}) have been investigated. Using the Vulcan Petawatt laser, with pulse duration of 1 - 2 ps at intensities greater than 10^{20} W cm^{−2}, electron energies up to 120 MeV with temperatures 20 - 30 MeV have been observed. A pre pulse was used to create an expanding plasma in which the high irradiance pulse was incident and the scale length of the pre pulse produced plasma was measured using optical probing. It was found that the number of hot electrons produced at 10^{20} W cm^{−2} linearly increases with the measured pre pulse plasma scale length indicating that the electron acceleration is dependent on the pre-pulse plasma volume. 2D PIC simulations are in agreement with experimentally measured temperatures, while 1D PIC simulations only agree for shorter scale length plasmas (L≤ 7.5 μm). Plasma channels are formed with longer scale length plasmas, but these channels do not result in greater acceleration of electrons as they are not sufficiently nar- row. The role of hot electrons in heating solid targets is experimentally examined and it is found that radiation effects on target heating when a pre pulse is present dominate over hot electron heating. |
