  The probability of electron-positron pair creation by a focused laser pulse
is calculated. For description of the focused laser pulse we use a
3-dimensional model of the electromagnetic field which is based on an exact
solution of Maxwell equations. There exists two types of focused waves: e- and
h-polarized waves with only either electric, or magnetic vector being
transverse respectively. It is shown that pair production is possible only in
$e$-polarized electromagnetic wave. The dependence of the pair production
probability on the intensity of the laser pulse is obtained. It is argued that
there exists a natural physical limit for attainable focused laser pulse
intensities. This limit is posed by the pulse energy loss due to the effect of
pair creation.
