Efficiency Enhancement for Kα X-Ray Yields from Laser-Driven Relativistic Electrons in Solids

High-irradiance short-pulse lasers incident on solid density thin foils provide high-energy, picosecond-duration, and monochromatic Kα x-ray sources, but with limited conversion efficiency ε of laser energy into Kα x-ray energy. A novel two-stage target concept is proposed that utilizes ultrahigh-contrast laser interactions with primary ultrathin foils in order to efficiently generate and transport in large quantities only the most effective Kα-producing high-energy electrons into secondary x-ray converter foils. Benchmarked simulations with no free numerical parameters indicate an ε enhancement greater than tenfold over conventional single targets may be possible.