influence of a laser profile in impedance mismatch techniques applied to carbon eos measurement

AbstractWe present a recent numerical analysis of impedance mismatch technique applied to carbon equation of state measurements. We consider high-power laser pulses with a Gaussian temporal profile of different durations. We show that for the laser intensity (${\approx }1{0}^{14} ~\mathrm{W} / {\mathrm{cm} }^{2}$) and the target design considered in this paper we need to have laser pulses with rise-time less than 150 ps

Investigating off-Hugoniot states using multi-layer ring-up targets

Laser compression has long been used as a method to study solids at high pressure. This is commonly achieved by sandwiching a sample between two diamond anvils and using a ramped laser pulse to slowly compress the sample, while keeping it cool enough to stay below the melt curve. We demonstrate a different approach, using a multilayer ‘ring up’ target whereby laser-ablation pressure compresses Pb up to 150 GPa while keeping it solid, over two times as high in pressure than where it would shock melt on the Hugoniot. We find that the efficiency of this approach compares favourably with the commonly used diamond sandwich technique and could be important for new facilities located at XFELs and synchrotrons which often have higher repetition rate, lower energy lasers which limits the achievable pressures that can be reached

Carbon equation of state at high pressure: the role of the radiative transport in the impedance mismatch diagnostics

A series of numerical simulation was performed on the application of the impedance mismatch technique to the experimental study of the equation of state (EOS) of porous carbon. Our conclusion is that this technique is useful for such a study up to laser intensities of the order of 1014 W/cm2 (in second or third harmonic of the Nd-laser). However, the inclusion of the radiation transport is important for the correct description of the shock propagation and can affect the results

Hydrodynamics of laser-produced plasma corona measured by optical interferometry

International audienceWe present the results of an experimental investigation of the temporal evolution of plasmas produced by high power laser irradiation of various types of target materials. We obtained 'high-quality' interferometric data on the evolution of the plasma electronic profile, which can be directly compared with analytical models and numerical simulations. For aluminium and plastic targets, the agreement with 1D simulations performed with the hydrocode MULTI is excellent, at least for large times (t ≥ 400 ps). In this case, simulations also show that the effect of radiation transport is negligible. The situation is quite different for gold targets for which, in order to get a fair enough agreement, we must take radiation transport into account

Modeling of freezing processes by an one-dimensional thermal conductivity equation with fractional differentiation operators

We have studied the Stefan problem with Caputo fractional order time derivatives. The difference scheme is built. The algorithm and the program for a numerical solution of the Stefan problem with fractional differentiation operator are created. For the given entry conditions and freezing ground parameters we have obtained the space-time temperature dependences for different values of parameter α. The functional dependences of the interface motion for the generalized Stefan conditions depending on the value of α are estimated. Finally we have found that the freezing process is slowed down during the transition to fractional derivatives