Experimental measurement of the wake field in a plasma filament created by a single-color ultrafast laser pulse.

Abstract

A laser plasma wake field in a single-color femtosecond laser filament determines the acceleration of ionized electrons, which affects the intensity and bandwidth of the emitted terahertz wave and is important for understanding the fundamental nonlinear process of THz generation. Since the THz wave generated by a laser wake field is extremely small and easily hidden by other THz generation mechanisms, no method exists to measure this wake field directly. In this paper, a simple and stable method for determining the amplitude of the laser plasma wake field is presented. Based on the cancellation of a positive laser plasma wake field and an external negative electric field, the "zero point" of the intensity of the generated THz wave at some frequency can be used to determine the exact amplitude of the corresponding laser plasma wake field. This finding opens an avenue toward the clarification of ultrafast electronic dynamic processes in laser-induced plasmas.