On e^+e^- pair production by a focused laser pulse in vacuum
  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. 
S. S. Bulanov (ITEP), N.B. Narozhny (MEPhI), V.D. Mur (MEPhI), and   V.S. Popov (ITEP)