Picosecond laser driven x-ray radiation enhanced by target normal sheath

Experimental results of x-ray radiation driven by picosecond laser on SGII-UP laser facility are presented. The PW laser beam which delivering 400J in 1 picosecond pulse was focused onto the foil target. The laser intensity on target is about 5-7×10¹⁸ W/cm². Different materials, from high atomic number Z material Tantalum, to middle Z material Copper, and low Z material plastic, were used as foil targets.  The target thickness is about 20 microns. The experimental results show that, x-ray radiation intensity of low Z plastic is a little lower than that of high Z Copper or Tantalum, but not that much as regular Bremsstrahlung expected. Also, x-ray radiation tends to be isotropic rather than along the laser direction. In which we believe target normal sheath field plays an important role.