Abstract

Summary form only given. Intense laser ablation induced shocks have been found use in the field of high pressure and high energy density physics studies viz. equation of state (EOS) measurements, phase transformations, understanding astrophysical high density plasma phenomena etc. Several megabars of pressures can now be generated, under laboratory conditions using modest laser intensities. To achieve higher shock pressure one must use short laser wavelength and higher intensity. However, at higher laser intensities, collective laser absorption processes dominate and consequently generate hot electrons and hard X-rays, leading to the preheat of the target material. This causes difficulty in generation of high target compression. To overcome this unwanted phenomenon we propose use of multilayered targets (two or more layers). From the laser irradiation side, the shock impedances of the layers are kept in an ascending order. Shock impedance mismatch at the interface of the layers cause a shock pressure jump, when an ablation shock is launched at the low impedance layer by a laser, reaches the interface. The pressure increase depends on the shock impedance mismatch of the layered materials. Our 1-D radiation hydro code simulations show that using a low density plastic layer on gold or aluminum substrate produce a shock pressure enhancement of 3 and 1.6 respectively at the interface. This data also has been corroborated by experiments in our laboratory. In this paper we propose to present our simulations and experimental data and show that in absence of the low impedance layer the laser intensity requirements are much higher. In addition, plastic being a low atomic number material generates very low X-ray yield and thus provides better ablation efficiency. We shall also present our simulation results using three layer targets. We believe that these results are very useful for studying materials in 20 to 40 megabar pressure range using very modest laser intensities

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