Observation of ultra-high energy density state in nanowire allay target with x-ray free electron laser SACLA

We have been developing to measure the heating process of nano-wire foils irradiated with ultra-high intensity laser. Experiments were performed at SACLA x-ray free electron laser facility. Ni Nano-wire alley foils (diameter ~ 0.2 μm, length ~ 10-20 μm, with Ni 20-μm-thickness substrate) were irradiated with Ti:Sappire laser at an intensity of around 10¹⁹ W/cm². The focal spot size and the pulse duration were around 20 μm and 25 fs, respectively. We measured shadowgraph images from side view with point source x-ray backlighting by SACLA at a photon energy around the K absorption edge of the Ni (~8.3 keV). The duration of the x-ray pulse was ~ 30 ps. We observed a temporal evolution of the heating region in the nano-wire region by changing the delay timing of the laser and the x-ray pulses.