Experimental Confirmation of Ponderomotive-Force Electrons Produced by an Ultrarelativistic Laser Pulse on a Solid Target

Abstract

First measurements of relativistic electrons produced by the interaction between a 400-fs, 1.06- $\mu \mathrm{m}$ ultrahigh-intensity laser pulse $(I>\mathrm{}{10}^{19}\mathrm{W}/{\mathrm{cm}}^2)$ and a solid target are presented. For electrons ejected along the laser propagation axis in the forward direction, the relation of the hot temperature $T_h$ versus the laser intensity $I$ is found to be in very good agreement with a $\mathbf{J}\times \mathbf{B}$ ponderomotive model described by S. C. Wilks et al. [Phys. Rev. Lett. 69, 1383 (1992)], where $T_h=({\gamma }_{\mathrm{osc}}-1\mathrm{}){\mathrm{mc}}^2$. Hot temperature of transverse electrons scales as $T_h\sim I^{1/3}$.