Observation of a highly directional γ-ray beam from ultrashort, ultraintense laser pulse interactions with solids

Novel measurements of electromagnetic radiation above 10 MeV are presented for ultra intense laser pulse interactions with solids. A bright, highly directional source of γ rays was observed directly behind the target. The γ rays were produced by bremsstrahlung radiation from energetic electrons generated during the interaction. They were measured using the photoneutron reaction ${[}^{63}\mathrm{Cu}{\mathrm{(\gamma ,n)}}^{62}\mathrm{Cu}]$ in copper. The resulting activity was measured by coincidence counting the positron annihilation γ rays which were produced from the decay of ${}^{\mathrm{62}}\mathrm{Cu}.$ New measurements of the bremsstrahlung radiation at ${10}^{19} {\mathrm{W cm}}^{\mathrm{-2}}$ are also presented.