Diagnosis of laser-induced relativistic plasma by positron imaging technique

Energetic deuterons emitted from laser-induced relativistic plasma are measured with a spatial resolution using a plate activated by them. Laser pulses of 33 TW in peak power and 34 fs in duration generate a plasma on a solid target, which is a microporous polytetrafluoroethylene film loaded with deuterated polystyrene, to accelerate deuterons. The deuterons are incident on a melamine plate, causing nuclear reactions of (12)C(d,n)(13)N and (14)N(d,n)(15)O. The spatial distributions of (13)N and (15)O created in the plate are visualized by a diagnosis using two-dimensional positron-emission tomography. The obtained images are further converted to temperature distribution of the emitted deuterons. The results show that the temperature of deuterons varies depending on the direction of deuteron emission. The present study provides knowledge of thermal equilibrium in laser-induced relativistic plasma in an ultrashort period of time.