Recent work on laser produced plasmas is presented focusing on the theoretical studies of four topics which have been carried out at the Institute of Laser Engineering (ILE), Osaka University, after a brief explanation of the six physics issues to be studied for plasma physics related to the laser fusion. The importance of integrated code development is emphasized and it is shown that the growth of the Rayleigh-Taylor instability at the ablation front is reduced partly due to non-local electron transport. Non-uniformity of implosion dynamics is studied by comparing a two-dimensional simulation with a spectroscopic post-processing package. It is concluded that all the available experimental data are consistently explained. The fast-ignition with ultra-high power laser is studied. The ignition criteria are clarified with a two-dimensional burning wave simulation. The possibility to study astrophysics by designing model experiments with intense lasers is introduced. The computational design of models of the ejecta-ring collision of SN1987A is shown by comparing with the event in the space.

An off-centre ignition model has been used to study the ignition conditions for laser targets related to the fast ignition scheme. A 2-D hydrodynamic code has been used, including alpha particle heating. The main goal of the study is the possibility of obtaining a high gain ICF target with fast ignition. In order to determine the ignition conditions, samples with various compressed core densities having different spark density-radius product (i.e. areal density) values were selected. The study was carried out in the presence of an external heating source, with a constant heating rate. A dependence of the ignition conditions on the heating rate of the external pulse is demonstrated. For a given set of ignition conditions, our simulation showed that an 11 ps pulse with 17 kJ of injected energy into the spark area was required to achieve ignition for a compressed core with a density of 200 g/cm3 and 0.5 g/cm2 spark areal density. It is shown that the ignition conditions are highly dependent on the heating rate of the external pulse.

The mutual interactions of two copropagating laser beams at a relative phase are studied using a two-dimensional fluid code. The interactions are investigated in underdense plasma at selected beam configurations and beam parameters for two separate nonlinearities, i.e., the ponderomotive and the relativistic nonlinearity. The selected beam configurations are introduced by different initial transverse spot size perturbations ͑finite and infinite͒ and different initial transversal intensity distributions ͑nonuniform and uniform͒ over those spot sizes and the selected beam parameters are given by different initial beam intensities relevant to each nonlinearity. In the ponderomotive nonlinearity, simulation results show that no mutual interactions are demonstrated between the copropagating beams regardless of the initial beam configurations and parameters. In nonlinear relativistic simulations, the mutual interactions between the beams are clearly observed, a mutual repulsion is formed in the presence of initial intensities that are nonuniformly distributed over finite spot sizes, and an effective strongly modulated mutual attraction takes places in the presence of initial intensities that are uniformly distributed over infinite spot sizes. Moreover, it is found in these simulations that increasing the initial beam intensities improves the attraction properties between the copropagationg beams.

We apply a Fourier pseudospectral algorithm to solve a 2D nonlinear paraxial envelope-equation of laser interactions in plasmas. In this algorithm, we first use the second order Strang time-splitting method to split the envelope-equation into a number of equations, next we spatially discrete the filed quantity and its spatial derivatives in these equations in term of Fourier interpolation polynomials (FFT), finally we sequentially integrate the resultant equations by means of a discrete integration method in order to obtain the solution of the envelope-equation. We carry out several numerical tests to illustrate the efficiency and to determine accuracy of the algorithm. In addition, we conduct a number of numerical experiments to examine its performance. The numerical results have shown that the algorithm is highly efficient and sufficiently accurate to solve the 2D envelope-equation, furthermore, it yields an optimal performance in simulating fundamental phenomena in laser interactions in plasmas.

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