Superradiant parametric x-ray emission

We compute a spectrum of parametric x-ray radiation inside crystal from bunch electrons, which is periodically modulated in density. consider that the electrons exiting an free-electron laser (XFEL) channel. demonstrate case resonance between frequency and modulation electron bunch, sequence strong quasimonochromatic pulses formed---superradiant emission (SPXE) with frequencies are multiples frequency. The number photons pulse SPXE extremely asymmetric diffraction comparable photon XFEL. Moreover, directed under large angle to velocity every harmonic emitted its own angle.