  Self-focusing of laser beam propagating through a dissipative suspension of
metallic nanoparticles is studied. Impact of imaginary part of nanoparticle
polarizability on the optical force and consequently on the particles
rearrangement in the presence of laser fields with an initial Gaussian profile
is considered. It is shown that considering absorption of wave, leads to the
creation of optical force along the wave travelling direction which can cause
longitudinal distribution of nanoparticles density. Considering fifth order
nonlinearity of wave amplitude that comes from simultaneous considering of
normal Kerr effect produced by the inhomogeneity of refractive index resulted
from ponderomotive force acting on electrons and artificial Kerr nonlinearity
caused by the polarization optical force acting on particles, set of
differential equations describing nonlinear steady-state evolution of laser
beam is derived by using a non-paraxial method. Evolution of laser spot size
for different frequencies is investigated and optimum frequency range for
improving focusing property is determined. It is shown that the artificial Kerr
effect causes concentration of particles near the propagation axis that can
reduce threshold power for occurring self-focusing.
