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 10 12 ) pulses to preserve target integrity. Here, we demonstrate a foam target that can efficiently absorb a common, low contrast 10 5 (in picosecond) laser at an intensity of 5 × 10 18 W/cm 2 , 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.
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