Generation of nonadiabatic laser pulse front from an overdense plasma

We suggest utilizing the interaction of an overdense plasma and an ultraintense laser pulse to generate extremely sharp (nonadiabatic) ramping-up of the pulse front. Due to the relativistic mass increase, the overdense plasma becomes partially transparent. As the boundary between the transparent and opaque region moves with a slow velocity, the laser pulse keeps being reflected by the boundary. After propagating through a couple of microns, the initial Gaussian pulse shape results in half-Gaussian shape. The different characteristics between the linear and circularly polarized pulse are discussed.