Proton Generation by Ultra-Short High-Power Laser and the Dependence on Laser Intensity and Pulse Duration

Abstract

Energetic protons (∼ 1.2 MeV) were generated by irradiation of ultra-short high-power laser pulses onto a 5 μm thick copper tape target and the dependence of the proton energies on the laser intensity and pulse duration were investigated. The laser intensity was varied between 8.5×10¹⁷ W/cm² and 6.6×10¹⁸ W/cm², and the pulse duration was varied from 55 fs to 400 fs. The maximum proton energy E_{p_max} and proton temperature were proportional to laser intensity, and they increased with the pulse duration when the laser intensity was kept constant. Thus far, E_{p_max} has been usually scaled as a function of laser intensity, but E_{p_max} depends not only on the laser intensity, but also on the pulse duration in an ultra-short pulse regime such as several tens of femto-seconds.