Fountain effect of laser-driven relativistic electrons inside a solid dielectric

Abstract

Ultrafast interferometry with sub-ps resolution has been applied for the direct measurement of an electron density induced by a laser-driven relativistic electron beam inside a solid dielectric. The topology of the interference phase shift shows the signature of the “fountain effect,” a narrow electron beam that fans out from the propagation axis and heads back to the target surface. Two-dimensional particle-in-cell (PIC) computer simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields. The very low ionization, ∼0.1%, observed after the heating pulse suggests a fast recombination at the sub-ps time scale.