  We consider the possibility of an experimental proof of vacuum e+e- pair
creation in the focus of two counter-propagating optical laser beams with an
intensity of the order of 10^20 - 10^22 W/cm^2. Our approach is based on the
collisionless kinetic equation for the distribution function of the e+e- pairs
with the source term for particle production. As a possible experimental signal
of vacuum pair production we consider the refraction of a high-frequency probe
laser beam by the produced e+e- plasma to be observed by an interference
filter. The generation of higher harmonics of the laser frequency in the
self-consistent electric field is also investigated.
