Optical and Transport Properties in Dense Plasmas Collision Frequency From Bulk to Cluster

Abstract

The dielectric function of dense plasmas is treated within a many-particle linear response theory beyond the RPA. In the long-wavelength limit, the dynamical collision frequency can be introduced which is expressed in terms of momentum and force auto-correlation functions (ACF). Analytical expressions for the collision frequency are considered for bulk plasmas, and reasonable agreement with MD simulations is found. Different applications such as Thomson scattering, reflectivity, electric and magnetic transport properties are discussed. In particular, experimental results for the static conductivity of inert gas plasmas are now well described.The transition from bulk properties to finite cluster properties is of particular interest. Within semiclassical MD simulations, single-time characteristics as well as two-time correlation functions are evaluated and analyzed. In particular, the Laplace transform of current and force ACFs show typical structures which are interpreted as collective modes of the microplasma. The damping rates of these modes are size dependent. They increase for the transition from small clusters to bulk plasmas.

Laser Excited Expanding Small Clusters: Single Time Distribution Functions

“…In bulk plasmas, extensive investigations of the dielectric function have been performed using the force autocorrelation function, see the review paper [40] and further references given there. For excited clusters, first preliminary considerations have been given in [33,36]. A static collision frequency was calculated from the damping rate of the momentum auto-correlation function and compared with larger rare gas clusters [41].…”

“…The Debye length λ D = [ε 0 k B T e /(e 2 n e )] 1/2 gives the screening length of the electron cloud around a charged particle. First calculations of optical properties for finite systems were presented in [32,33]. Results for optical response taking MD calculations of laser excited sodium clusters of different sizes were compared with each other and with bulk systems.…”

Relaxation and collective excitations of cluster nano-plasmas

“…where T is an instantaneous temperature. The previous simulation results [25,26] show that the typical time between electron emissions is much greater than the time for the local equilibrium build up in the electron subsystem.…”

“…Using this method in Refs. [25][26][27][28] the time evolution of the electron subsystem has been computed in dependence on the above mentioned parameter values R i , n i , and T .…”

Spatially resolved collective excitations of nano-plasmas via molecular dynamics simulations and fluid dynamics

“…In the case of clusters, the correlation functions were analyzed using spherical harmonics. In order to bridge from finite systems to bulk plasmas, first results with respect to size effects have been reported in [9,14]. In particular, we are interested in the dynamical structure factor and the response function for such finite nano-plasmas, which are related specifically to correlation functions of the spatially resolved electron density fluctuations.…”