Spontaneous and induced radiation by electrons/positrons in natural and photonic crystals. Volume free electron lasers (VFELs): From microwave and optical to X-ray range

Spontaneous and induced radiation produced by relativistic particles passing through natural and photonic crystals has enhanced capabilities for achieving the radiation sources operating in different wavelength ranges. Use of a non-one-dimensional distributed feedback, arising through Bragg diffraction in spatially periodic systems (natural and artificial (electromagnetic, photonic) crystals), establishes the foundation for the development of volume free electron lasers/masers (VFELs/VFEMs) as well as high-energy charged particle accelerators. The analysis of basic principles of VFEL theory demonstrates the promising potential of VFELs as the basis for the development of high-power microwave and optical sources.