Laser Plasma Interaction Experiments at Utsunomiya University

Summary form only given. At Utsunomiya University, the radiation generation experiments and the laser guiding experiments with capillary discharge plasma using a short and ultra high intense laser (1 TW/100 fs) have been carried out. When the laser is tightly focused in the neutral gas, we observe the strong radiation in the microwave regime. The radiation generated from the focal region is strongly polarized and emitted in the conical direction. The frequency of the radiation is 200 ps and its frequency is broad in the microwave region (~100 GHz). Diagnostics used are by the horn antenna, waveguide and a microwave detector and time-of-flight method for the frequency measurement. This radiation can be explained by the Cherenkov theory, assuming the propagation of the ionization front created by the laser is close to the speed of light in the media. On the other hand, the capillary discharge experiment is carried out using a pulsed discharge power supply (30 kV, 300 A, 10 Hz). When the high voltage pulse is applied to gas-filled capillary (1 mm dia./1 cm long), the surface discharge occurs and the plasma is created inside of the capillary. The working gas is argon. The plasma density is measured to be 10¹⁶-10¹⁷ cm^-3 by the interferometer technique and it depends on the gas density and the applied voltage. When the long pulse Nd-YAG laser (6 ns) is introduced to the capillary, the laser guiding is observed. The laser diameter is changed when the plasma density changed. The optimum plasma density for the guiding is observed