Mitigation of laser imprinting with diamond ablator for direct-drive inertial confinement fusion targets

Diamond is very hard material, and uncompressible under its elastic limit ($\sim$ 180 GPa), which means that diamond has a very large effective specific heat ratio. Since the imprint efficiency is a function of the specific heat of the target material, diamond is a promising candidate for the ablator material. We carried out an experiment to measure the target imprinting on diamond foils. The thickness of the diamond foils were 8-15 $\mu $m. We also irradiated polystyrene foils as a reference in order to compare the imprint level. The intensity modulation was imposed for the foot pulse with the wavelength on the target of $\sim$ 100 $\mu $ m. The intensity of the foot pulse was $\sim$ 5 x 10$^{12}$ W/cm$^{2}$ followed by the main pulse ($\sim$ 1 x 10$^{14}$ W/cm$^{2})$ to accelerate the foil. Areal density perturbation was measured with face-on backlighting technique. The imprint amplitude was evaluated by measuring areal density perturbation which is amplified by Rayleigh-Taylor instability while the target is accelerated after the target imprinting with a foot pulse.