Measuring the electron density gradients of dense plasmas by deflectometry using short-wavelength probe

Abstract

A new and simple experimental technique for the measurement of electron density gradients in dense laser-produced plasmas using an electromagnetic wave probe is presented. The main advantage of this method is the low requirements on coherence of the probing beam. The method is based on measuring the deformation of the Talbot pattern of a two-dimensional grating that stems from the distortion of the probe beam wave-front caused by the gradients of the index of refraction. The compromise between spatial resolution and sensitivity for the given wavelength of the probe beam is set by the experimental design. The proposed technique was experimentally verified on plasmas that were created by either a point focus or a line focus of a laser interacting with various solid targets. In the experiments reported here, all plasmas were probed by a Ne-like Zn x-ray laser beam at 21.2 nm, but the technique is applicable for any wavelength of the probe.