Development of diffraction electronics in IRE NAS of Ukraine

S. Smith and E. Purcell where the first who observed optical radiation of electrons moving over diffraction grating [1]. Only in 10 years after that seminal experiment, the first theoretical work on the theory of the Smith-Purcell radiation, or Diffraction Radiation Effect was reported at the $3^{rd}$ All-Union Symposium on Wave Diffraction (Tbilisi, September 1963) [2]. In more detail, the obtained results were published one year later in the $7^{th}$ Issue of the "Radio Engineering and Electronics" journal in the paper "Radiation of electromagnetic waves by an electron beam moving over a diffraction grating" (O.A. Tretyakov, S.S. Tretyakova, and V.P. Shestopalov) [3]. The authors pointed to the possibility of using the diffraction radiation to produce EM waves either by modulated electron beam or by short bunches of electrons flying over the periodic structure. Though in this work the creation of a self-oscillator was not discussed, nevertheless, the authors already then thought about the implementation of this effect in the microwave range, proposing to obtain a modulated electron beam with the help of a photocathode irradiated by superposition of two lasers beams with different frequencies, which provided modulation of the photocurrent at the difference frequency. Further, as far as we know, professor Victor P. Shestopalov has made multiple attempts to attract experts in the field of microwave electronics to design a new millimeter-wave generator, based on the diffraction radiation. However, he had to arrange this research himself with essential support by Olexandr Usikov, Director of the IRE NASU, Kharkiv. As a result, a new research area in millimeter and sub-millimeter wave (THz) vacuum electronics was founded by Victor Shestopalov in IRE NASU, and it has been under intense research and development during the following 35 years under his leadership. In the Victor P. Shestopalov School, the very effect of diffraction radiation (Smith-Purcell radiation), i.e., the bulk radiation of a charge moving near the diffraction grating surface, was considered as the main physical effect necessary to create an oscillator on bulk wave feedback, but not on surface ones. The provision of feedback and the choice of an oscillatory system had to follow from the features and patterns of this radiation, from the electromagnetic laws and the excitation theory of OR. The next step might be a theory of related self-oscillatory system. That is why a new device was named as Diffraction Radiation Oscillator (DRO). The DRO study has been carried out theoretically, experimentally and technologically. The goals of the research were both in-depth understanding of the physical phenomena occurring in DRO and the developing of the devices which should meet requirements of various applications in millimeter and submillimeter wavelength ranges (35-500 GHz).