Near-complete absorption of intense, ultrashort laser light by sub-λ gratings

We demonstrate near-100% light absorption and increased x-ray emission from dense plasmas created on solid surfaces with a periodic sub-λ structure. The efficacy of the structure-induced surface plasmon resonance, responsible for enhanced absorption, is directly tested at the highest intensities to date (3×1015W cm-2) via systematic, correlated measurements of absorption and x-ray emission. An analytical grating model as well as 2D particle-in-cell simulations conclusively explain our observations. Our study offers a definite, quantitative way forward for optimizing and understanding the absorption process