Density profile of a line plasma generated by laser ablation for laser wakefield acceleration

Abstract

An elongated line plasma generated by a laser ablation of an aluminum target was investigated, which can be used in the laser wakefield acceleration (LWFA) by employing ultra-intense laser pulse through the longitudinal direction of the plasma. To generate a uniform and long plasma channel along the propagation of ultra-intense laser pulse (main pulse), a cylindrical lens combined with a biprism was used to shape the intensity of a ns Nd:YAG laser (pre-pulse) on the Al target. A uniformity of laser intensity can be manipulated by changing the distance between the biprism and the target. The density profile of the plasma generated by laser ablation was measured using two interferometers, indicating that a 3-mm long uniform line plasma with a density of 6 × 1017 cm−3 could be generated. The density with main pulse was also measured and the results indicated that the density would increase further due to additional ionization of the plasma by the main ultra-intense laser pulse. The resulting plasma density, which is a crucial parameter for the LWFA, can be controlled by the intensity of the pre-pulse, the time delay between the pre- and main pulse, and the distance of the main pulse from the target surface.