Picosecond time-resolved X-ray holography

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We faced a problem of insufficiency of laser plasma X-ray intensity at the start of this study for X-ray holography. Then, making a change in our plan, we aimed time-resolved imaging of a laser ablation process with 10 ps time resolution and tried to take X-ray absorption images of metallic materials and organic materials. It was found possible that sufficient image contrast would be achievable in 10 shots for metallic samples and 100 shots for organic materials. Thus, X-ray enhancement to the extent of 10 〜 100 times was necessary in order to make a single-shot imaging. The yield of the laser plasma X-ray is strongly dependent on the pre-plasma distribution. We investigated the condition of the pre-plasma with numerical simulations and found that the amount of X-rays would be increased 10 times by suppression of the pre-plasma expansion. Several experiments were carried out to improve the laser contrast. Those methods, however, were not applied to actual an X-ray generation experiment at this time. The number of photons of CuKa generated from a laser plasma was estimated experimentally as 4.4 x 10^9 [photons/shot/4 π sr]. Laser contrast was improved about one order ( ASE intensity 〜 10^12 W/cm^2). The efforts to improve the laser contrast such as phase transition in a semiconductor crystal, relativistic self-focus in a gas-jet, and metal-coated targets are continued. X-ray yield is going to increase more than ten times by pre-pulse control. We expect further increase of X-rays because of the laser upgrade to be done in the near future.