Scaling relativistic laser-solid interaction using 30fs laser pulses*

There has been growing interest in relativistic laser-solid interaction as a compact source of relativistic electron beams and hard x-rays. Femtosecond hard x-ray pulses have important applications such as probing time-resolved x-ray absorption and diffraction. Relativistic electrons from solid targets have superior properties in beam charge and divergence than those from wakefield acceleration in underdense plasmas, and can find applications in warm dense matter creation, electron radiography, seed of wakefield accelerators and fast ignition researches. In this work, the 30fs laser pulses are focused down to near diffraction-limit spot size to achieve relativistic intensity (a\textunderscore 0\textgreater 1) and ablate into a thick (\textasciitilde mm) glass target. We investigate the scaling laws of this interaction in terms of laser wavelength (0.8\textmu m, 1.3\textmu m and 2\textmu m), laser energy (millijoule to joule level), angle of incidence (grazing, 45\textdegree and normal) and preplasma scale length (0.1$\lambda $ to 5$\lambda )$. Particle-In-Cell simulation (PIC) and particle tracking shows that the incident half and reflected half of the laser pulse form a standing wave to accelerate electrons to relativistic (MeV) energy.