Study Of The Optical Properties Of Strongly Coupled Plasmas

Strongly coupled plasmas are subject of intense research. The continuous and even growing interest originates from fundamental theoretical problem that have to be solved for all many-particle systems with long-range Coulomb interaction and from diverse applications. In this work, the optical properties of strongly coupled plasmas are investigated including the linear response theory of plasma, X-ray Thomson scattering and free-free absorption of radiation.Dielectric function is the central aspect of linear response theory. The electron RPA dielectric function is calculated using our code for the whole wave vector and frequency space. The dependent on each variable is studied from which the dispersion relationship of plasmon is obtained at the zero of dielectric function. In addition, the impact of density and temperature effects on plasmon is also considered. The strength of collective excitation enhances with the increase of density and the decrease of temperature.The light scattering spectrum of plasma is determined by the dynamic structure factors which are calculated in the Born-Mermin approximation at different densities and temperatures up to the strongly coupled region for three sets of modeling scattering geometry. In the collective scattering regime, two asymmetry peaks appear on the curves mark the plasmon positions according to the dispersion relationship. Also the PRA results are given here as a comparison. Collisions turn out to broaden and give a redshift to the peaks. At the high densities, the effect of collision becomes weak due to Pauli blocking.The free-free absorption coefficients of plasmas at low photon energy are calculated from the dielectric function theory. By introducing a dynamical collision frequency, the effects of dynamical screening, collective excitation of electrons and correlation of ions are taken into account. The free-free absorption coefficients are investigated for aluminum plasmas at the temperature of 10000 K and densities of 0.025, 0.1, 0.3, 0.5, 1.0, and 2.0 g/cm3. At near solid density where the coupling is strong, our calculated results agree well with those of the quantum molecular dynamics reported in the literature. This shows the validity of our approach in dealing with the nonideal effects in warm dense plasmas. Comparisons are also made with the classical Kramers absorption coefficient and the results show that the latter one is approximately applicable only at the low densities.