GENERATION OF X-RAY-RADIATION IN ATOMS SU BJECTED TO AN ULTRAHIGH-INTENSITY LASER FIELD

A semiclassical approach is used to describe the generation of high op tical harmonics in atoms subjected to an ultrahigh-intensity laser fie ld. Account is taken of the influence of the Coulomb potential and of the relativistic effects on the motion of an electron in a continuum, of the spreading of a wave packet of an electron in a continuum, and a lso of the depletion of atomic states. This approach leads to a predic tion of a new effect: nonmonotonic behaviour of the intensities of the individual harmonics in a certain range of intensities of the pump fi eld in the form of extremely short laser pulses. It is shown that effi cient generation of harmonics with the orders as high as 1000 is feasi ble.