Rayleigh scattering of a Gaussian laser beam from expanding clusters

Abstract

Rayleigh scattering of an intense laser with Gaussian temporal and radial profiles from clustered gases is examined. The laser quickly converts the clusters into plasma balls with electron cloud of each ball executing large excursions about the ion sphere. The laser also heats the electrons. As the clusters expand under hydrodynamic pressure, plasma frequency of the cluster electrons ωpe decreases. The temporal rate of decrease in ωpe is maximum on laser axis and falls off with r. As the electron density of a cluster approaches plasma resonance, ωpe=ω3 (where ω is the frequency of the laser) the oscillatory electron cloud of the cluster produces resonantly enhanced Rayleigh scattering. This resonant enhancement first occurs in clusters on laser axis and afterward in farther clusters. The diffraction divergence of the laser limits the length of the cluster plasma, hence the Rayleigh scattering.