Enhanced focusing of relativistic lasers by plasma lens with exponentially increasing density profiles

Abstract

The self-focusing of ultraintense laser in plasma lenses with exponentially increasing density profiles is studied. And the robustness of this design is proved by theoretical estimates and 3D particle-in-cell simulations. Attributed to the density compensation for the increase of laser intensity during self-focusing, a modulated exponential density plasma lens can efficiently focus the laser to higher peak intensity and smaller spot than that by using optimized uniform plasma lens. In near critical density plasmas, laser focusing experiences two stages with different dominant mechanisms: self-focusing at earlier time and magnetic constraint in the plasma channel. And more enhanced effects are achieved by exponential density plasma in both stages. The focal position and the optimal density scalelength for this kind of plasma lens are also estimated through theoretical derivation. Our findings indicate the possibility for the preplasma to experimentally serve as a novel plasma lens to obtain relativistic lasers with high contrast, ultra-high intensities and micro focal spots.