  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.
