Study of pico second movie of plasma interaction with optical vortex and particle acceleration

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1) Generation of ultra-short-pulse optical vortex using spiral phase shifter: A spiral phase shifter was fabricated by coating a 16-steppatterned SiO* onto a glass substrate. The phase distribution was in good agreement with that predicted by the computed hologram, and then an optical vortex (Laguerre-Gaussian beam with a topological charge of 1) was successfully obtained.2) Imaging with sub-ps time resolution: A 130-fs ultra-short Ti: sapphire laser pulse was frequency doubled. Then optical probe system was constructed using this UV pulse for measuring short-life plasmas by shadowgraphy and interferometer techniques. The propagation of ultra-short-pulse laser light and the dynamics of plasma formation were observed using this probing system, and their dependence on laser phase/polarization distributions was studied.3) Generation of longitudinal electric field from laser: A linearly polarized light was converted to axially symmetric polarization (radial polarization and azimuthal polarization) with an efficiency greater than 90% using a polarization distributed plate based on an optical rotatory of liquid crystal. A longitudinal electric field of 10*V/m was observed near a focal spot of 0.45-MW radially polarized Nd: YAG laser. Thus 0.1TV/m can be realized using a TW class high power laser.4) Particle acceleration with optical vortex and radial polarization: Ti: sapphire laser pulse of 0.5-1TW was focused onto a solid or gaseous target. The measured electron spectra suggest that these special laser modes can enhance the amount of forward accelerated electrons especially in high energy component.5) Particle simulation: A particle simulation code has been newly developed for the analysis of the effects caused by the phase/polarization distribution. This code showed that the substantial increase of high-energy electrons for combining the Laguerre-Gaussian beam with circular polarization.