Micro-optics for ultra-intense lasers

Abstract

Table-top, femtosecond lasers provide the highest light intensities capable of extreme excitation of matter. A key challenge, however, is the efficient coupling of light to matter, a goal addressed by target structuring and laser pulse-shaping. Nanostructured surfaces enhance coupling but require "high contrast"(e.g., for modern ultrahigh intensity lasers, the peak to picosecond pedestal intensity ratio >1012) pulses to preserve target integrity. Here, we demonstrate a foam target that can efficiently absorb a common, low contrast 105 (in picosecond) laser at an intensity of 5 × 1018 W/cm2, giving ∼20 times enhanced relativistic hot electron flux. In addition, such foam target induced "micro-optic"function is analogous to the miniature plasma-parabolic mirror. The simplicity of the target - basically a structure with voids having a diameter of the order of a light wavelength - and the efficacy of these micro-sized voids under low contrast illumination can boost the scope of high intensity lasers for basic science and for table-top sources of high energy particles and ignition of laser fusion targets.