  From Vlasov kinetic equation for collisionless plasmas distribution function
in square-law approximation on size of electromagnetic field is received.
Formulas for calculation electric current at any temperature (any degree of
degeneration of electronic gas) are deduced. The case of small values of the
wave numbers is considered. It is shown, that the nonlinearity account leads to
occurrence the longitudinal electric current directed along a wave vector. This
longitudinal current orthogonal to known transversal classical current,
received at the linear analysis. From the kinetic equation with Wigner integral
for collisionless quantum plasma distribution function is received in
square-law on vector potential approximation. Formulas for calculation electric
current at any temperature are deduced. The case of small values of wave number
is considered. It is shown, that size of a longitudinal current at small values
of wave number and for classical plasma and for quantum plasma coincide.
Graphic comparison of dimensionless size of a current quantum and classical
plasma is made.
