Experimental Research on Ultra Intense Magnetic Field in plasma Produced by Circularly Polarized Laser Light

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On the laser-plasma interaction using the ultra-short pulse, intense laser, we have done the experiments relevant to the magnetic field generation depending on the laser polarization. The distinctive characteristics and performances are as follows;1) Development of liquid crystal wavelength plate for the laser polarization control :To achieve the laser-assisted alignment control of liquid crystal (LC), we adopted the photo-isomerization effect of azo dyes doped into the alignment layer of LC. The LC alignment was spatially controlled using the linearly polarized ultra violet light (UV : the third harmonic of Nd : YAG laser or a Hg lamp), then the arbitrary polarization/phase pattern was demonstrated by spatially changing the polarization direction of UV light.2) Experimental set up of laser-plasma interaction and ultra-short pulse laser probe :A laser used in this study was Ti : sapphire laser operated with the chirped pulse amplification/compression (wavelength 【approximately equal】 800 nm, pulse width 【approximately equal】 120 fs, output power 【approximately equal】 1 TW, irradiation intensity 【approximately equal】 4×10ィイD116ィエD1 W/cmィイD12ィエD1). A small part of this output was split out as a probe beam which was frequency doubled using a thin Type-I KDP crystal. The synchronization between the main laser pulse and the probe pulse is adjusted by use of Michelson interferometer technique (the first order cross correlation) with an accuracy of 〜 100 fs.3) Interaction experiments :In this term of project, although the polarization dependence on the magnetic field generation was not observed because of an insufficient plasma formation, following new phenomena were observed. a) The efficiency of forward acceleration of energetic ions (protons) was several times higher for the circular polarization compared with linear polarization. b) The self-focusing and beam break-up in the plasma was clearly observed by the ultra-short pulse shadowgraph.