Smith–Purcell frequency multiplier with synchronization of radiation from a wide electron beam

Abstract

An orotronlike feedback can provide a significant increase in the selectivity and power of frequency-multiplied Smith–Purcell radiation of the electron bunches formed in the course of self-excitation of a grating surface eigenmode. This method looks promising for efficient terahertz generation from both weakly and mildly relativistic electron beams.

Smith-Purcell Based Terahertz Frequency Multiplier: Three Dimensional Analysis

“…However when the beam size comes to be far larger than the wavelength of the surface mode, different transverse parts of the beam would be capable of excitement of different transverse surface modes. Hence their frequencies and phases are marginally altered and the optical beam diffuses [7]. This is already mentioned for SP backward wave oscillators (BWOs) that they will not operate with an infinitely wide grating [22].…”

“…This device is abstractly shown in Fig. 9.1 and is frequently studied in electron-beam driven frequency multiplication processes [17] and certainly it is a promising candidate for producing terahertz radiation [7,[18][19][20]. As discussed in the most of theoretical studies [19] and in experimental ones [21], SPR power is still very low which its origin seems to be from its spontaneous nature.…”

“…Smith-Purcell radiation (SPR) [6] mechanism is based on excitation of "surface eigenwaves" [7,8] above a metallic gratings. This phenomenon is considered to be one of the most interesting methods of generating sub-millimetre waves mainly in THz realm [9][10][11][12][13][14][15][16].…”

“…Yet it is able to play the role of a compact THz radiation source in a diverse range of uses such as spectroscopy and diagnostics of different media. [7] The metallic structures are assumed to be made of perfect conductor and unlike the experimental cases [21] in which pencil-like electron beams are used, a sheet electron beam is implemented as electron source. Through enhancing the interaction of electron beam and surface wave, the operating current and output power will increase.…”

Experimental demonstration of Smith–Purcell radiation enhancement by frequency multiplication in open cavity

“…In contrast to the numerous papers [9][10][11][12][13][14][15][16][17][18] where the open grating itself is considered as an electrodynamic system of such multipliers, we propose to use for such a device a two-mirror open cavity similar to the orotron one, which provides effective feedback for a definite frequency harmonic. 8,19,20 In the proposed regime ͓Fig. 1͑a͔͒, the orotron periodic structure serves simultaneously as a cavity for low-frequency surface ͑evanescent͒ waves.…”