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The idea and principles of volume free electron lasers were proposed in [1-4]. It was shown there that volume distributed feedback (VDFB) can essentially reduce the threshold current of generation and provide the possibility of smooth frequency tuning. The present work considers an undulator VFEL with multiwave VDFB. It is shown that dependence of threshold current on the interaction length changes in the point of roots degeneration. This leads to the sharp decrease of start current if condition of dynamical diffraction is fulfilled. The dependence of amplification coefficient changes, too. So the interaction length for generation appears shorter. The proposed scheme can be used for generation in wide spectral range from microwaves to X-rays. The operating features of undulator VFEL is considered., Comment: Latex, 6 pages with 2 Postscript figures

Volume Free Electron Laser (VFEL) was proposed in [1-4]. It can operate in the wide spectral range from microwaves to X-rays. To simulate the processes which take place in VFEL the superradiance from a short electron pulse moving in a volume diffraction grating is studied in wavelength range ~4 mm. It is supposed that Bragg condition for emitted photons is fulfilled and dynamical diffraction takes place. The spectral-angular distributions for transmitted and diffracted waves are derived. It is shown that the optimal geometry of diffraction exists and is determined by the energy and transverse size of electron beam., Comment: Latex, 5 pages with 1 Postscript figure

Effect of guiding magnetic field on evolution of stimulated emission is considered. It is shown that the transverse dynamics of electrons contributes to generation process and that contribution decreases with the magnetic field grows. The equation of generation for stimulated radiation of electron beam passing over periodic medium in magnetic field of arbitrary value is derived. The critical value of guiding field for which the transverse dynamics of electron don't contribute to emission is determined. It is shown, that transverse dynamics of electron modifies the boundary conditions. It follows from the derived generation equation that transverse dynamics yields to ~25% increase of the increment magnitude in high gain regime. In the limit of small signal the generation gain twice increases when transverse dynamics evolves. Obtained results are valid for every FEL system, which use the mechanism of waves slowing in the slow-wave structures for generation., Comment: Latex, 14 pages with 4 Postscript figure