ИСТИНА

Using two-dimensional numerical PIC simulations, generation of incoherent X-ray pulses in the pump-probe scheme including two super intense laser pulses and a plasma layer is considered. When a non-adiabatic laser pulse of relativistic intensity falls normally at a thin plasma layer, a simultaneous longitudinal (relative to the axis of the laser beam) displacement of all electrons can occur under the action of the longitudinal component of the Lorentz force. With a sufficiently large field amplitude, this force accelerates electrons to relativistic velocities. As a result, a relativistic electron mirror with a diameter of the order of several microns and with a thickness of several nanometers or less can be prepared by the pump or accelerating laser pulse from a plasma layer. After some time delay, another counter-propagating laser pulse, which can be called a probe pulse, scatters off this relativistic electron mirror, producing X-ray radiation. Both coherent and incoherent parts in the scattered radiation can be formed. For the coherent part of the radiation, the shape of the reflected pulse resembles that of the counter-propagating pulse. The reflected pulse frequency is proportional to the normalized energy of the electrons in the relativistic electron mirror. For the incoherent part, the scattered radiation frequency is proportional to the square of the normalized electrons energy and can be considerably larger than that for the coherent radiation. So an all-optically driven backscattered X-ray source is implemented in this scheme. The parameters of a relativistic electron mirror largely determine the characteristics of X-ray pulses. Such mirrors can be produced from different targets – nanofoils, gas jets, foamed materials with near-critical density, etc. It is shown that the main parameters of the generated radiation, i.e. frequency (or energy of the generated quanta), amplitude, duration, spectral properties, etc., can be easily controlled. The characteristics of the incoherent X-ray pulses produced in the pump-probe scheme for different parameter sets of the plasma layer, accelerating and probe laser pulses were investigated in details. The scaling of the generated X-ray quanta energy and their number with the amplitudes of the accelerating and probe pulses as well as with the plasma electron density was studied. It is shown that the brightness and directionality of the X-ray radiation can be very high.