Characterization of x- and gamma- radiation in relativistically intense laser-solid interactions

Using a high resolution ($\lambda $/$\Delta \lambda $\textgreater 100) high purity germanium detector, the angular and material dependence, and the intensity scaling, of bremsstrahlung gamma radiation from relativistically intense (I\textgreater 10$^{\mathrm{18}}$ W/cm$^{\mathrm{2}})$ laser-solid interactions have been characterized at energies between 0.1 and 1 MeV with the high-repetition rate (500 Hz) Lambda-Cubed laser facility. The bremsstrahlung spectra of SiO$_{\mathrm{2}}$, Mo, and Eu$_{\mathrm{2}}$O$_{\mathrm{3}}$ were observed to have two-temperature energy distributions, corresponding to two different groups of electrons and depending on both laser intensity and observation angle. The spectra and source sizes of hard x-radiation under 0.1 MeV are also studied. These x-ray sources are being developed for phase-contrast imaging.