Development of a method for detecting γ-rays from high-energy laser plasma and test experiments

With advances in laser technology, the achievable laser intensity at focus is increasing every year. As a result, the energy of electrons emitted from the solid density plasma produced by laser irradiation has reached several tens of MeV of temperature.

Under these circumstances, nuclear reactions are considered to be taking place in the interaction between the intense laser pulse and the target material. In this study, we aimed to measure γ-rays generated by irradiating 5-μm thick Ag target with a high-intensity short-pulse laser called J-KAREN at the Kansai Institute for Photon Science. Laser plasmas emit a large number of high energy photons, which are difficult to measure with scintillators due to pile-up effect. The purpose of this study is to develop a new diagnostic technique that will serve as a basis for laser plasma physics.

Here, a detector called an emulsion (nuclear emulsion) is used to detect the electron-positron pairs produced via the pair production by γ-ray while visualizing them. Because emulsions have high spatial resolution of submicron, the angle, energy, and flux of the incident γ-rays can be reconstructed with high precision, it makes easy to determine whether the photons are from the direction of target or not.

The development status of γ-rays measurement technique using emulsions and the detail of the detection method with emulsions will be reported.