Temperature scaling of hot electrons produced by a tightly focused relativistic-intensity laser at 0.5 kHz repetition rate

The energy spectrum of hot electrons emitted from the interaction of a relativistically intense laser with an Al plasma is measured at a repetition rate of 0.5 kHz by accumulating ∼ 10 3 highly reproducible laser shots. In the 10 17 - 2 × 10 18 W / cm 2 range, the temperature of electrons escaping the plasma along the specular direction scales as ( I λ 2 ) 0.64 ± 0.05 for p -polarized pulses incident at 45°. This scaling is in good agreement with three-dimensional particle-in-cell simulations and a simple model that estimates the hot-electron temperature by considering the balance between the deposited laser intensity and the energy carried away by those electrons.