Efficiency and scaling of an ultrashort-pulse high-repetition-rate laser-driven X-ray source

Technical issues and performance of a high-repetition-rate ultrafast-laser-based X-ray source have been studied experimentally in the context of developing a dedicated laboratory-based tool for combustion diagnostics. X-ray emission from numerous elemental materials have been investigated to compare with analytical based expectations for yield and efficiency, as well as to evaluate advantages of some materials for operational issues such as debris production and degree of efficiency enhancement utilizing various illumination configurations. A weak inverse scaling of conversion efficiency with atomic number was observed. Broadband energy conversion efficiency of approximately 10(-5) and yield greater than 10(10) photons/s have been measured with numerous target elements. Application of a pre-pulse significantly enhances conversion efficiency, and the enhancement factor depends on material. Thus, previous optimizations must be performed in the atomic number variation as well. Additionally, the efficiency enhancement associated with p-polarization incidence (relative to s-polarization) is observed to depend on base material reflectivity.