Speed of Opening a Relativistic Transparent Channel in an Overdense Plasma by a Linearly Polarized Wave

Abstract

We investigated by theory and simulations how fast a relativistically transparent channel is opened by a linearly polarized relativistic laser pulse in an overdense plasma, which is classically opaque. The relativistic transparency has been well known: the dispersion relations were revealed for various steady states. However, as long as we understand, the answer to the question `how the relativistic channel is formed dynamically from an opaque plasma' has not been so clear. In this work, we focused on finding analytically the speed of such a channel opening. By employing the `channel-opening-time' concept, we could derive semi-analytically a simple formula, which showed excellent agreement with the one-dimensional PIC simulations. The theory was successfully applied in predicting the pulse shape after the interaction of an ultraintense linear polarized laser pulse and a thin foil both in one- and two-dimensional systems.