Use of dynamical undulator mechanism to produce short wavelength radiation in volume FEL (VFEL)

VFEL lasing in a system with a dynamical undulator is described. In this system radiation of long wavelength creates the undulator for lasing at a shorter wavelength. Two diffraction gratings with different spatial periods form the VFEL resonator. The grating with longer period pumps the resonator with the long wavelength radiation to provide the necessary amplitude of the undulator field. The grating with the shorter period is used to select the mode for the short wavelength radiation. Lasing of such a system in the terahertz frequency range is discussed.