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Excitation of induced coherent Smith–Purcell (SP) radiation by relativistic magnetized electron beam in the absence of the resonator is considered within the framework of the dispersion equation. We have found that the dispersion equation for the SP instability is a quadratic equation for frequency. The first-step approximation for solution of the dispersion equation, giving the SP-spectrum of frequency, corresponds to the mirror boundary case, when the electron beam propagates above a plane metal surface (mirror). It was found that the conditions for both the Thompson and the Raman regimes of excitation do not depend on beam current and depend on the height of the beam above the grating surface. The growth rate of the instability in both cases is proportional to the square root of the electron beam current. No feedback is needed to provide the coherent emission.

A Smith–Purcell (S–P) free electron laser (FEL) composed of a metallic diffraction flat grating, an open cylindrical mirror cavity and a relativistic sheet electron beam with moderate energy, is presented. The characteristics of this device are studied by theoretical analysis, experimental measurements and particle-in-cell (PIC) simulation method. Results indicate that coherent radiation with output peak power up to 50 MW at millimeter wavelengths can be generated by using relativistic electron beam of moderate energy.

The frequency-tunability for a Smith-Purcell free-electron laser oscillator in the millimeter wave region is enhanced with the aid of a quasi-periodic distributed Bragg reflector (DBR) made of metallic waveguide gratings with rectangular grooves. For a quasi-periodic DBR, the grating parameters are adjusted by means of genetic algorithms to get the desired reflection coefficient, thus compensating for the frequency dependence of the overall output characteristics. For a typical numerical example, flat output characteristics have been obtained over 10% bandwidth around the center frequency 121 GHz

Electrons from a source in a solenoidal magnetic field emerge from that field with a characteristic angular momentum. This behavior can be used to produce a flat ribbon-like electron beam with zero thickness (to first order). We show that this can be done using a quadrupole triplet and provide analytical expressions for the focal length of each lens. Solutions can be found over a wide range of practical values of the parameters.

A novel Smith–Purcell (SP) free-electron laser (FEL) with axial-symmetrical structure is proposed. The distribution of the high frequency field in the resonator is analyzed and the operating frequency and output power are also studied by the use of particle-in-cell (PIC) simulation method. Results indicate that coherent radiation with output peak power up to 58 MW at millimeter wavelengths can be generated by using relativistic electron beams of moderate energy.

The paper describes emission characteristics of semiconductor cold cathodes such as Si-field emitters and metal-oxide-semiconductor (MOS) electron tunneling emitters, and shows that their characteristics reflect the semiconductor property or the electron transport in an incorporated semiconductor device. The paper also describes Smith–Purcell radiation experiment as one of the device applications of semiconductor field emitters.

In this work we suggest as a source of terahertz radiation a waveguide – dielectric pipe with periodic internal radius and electrons moving through it. The resulting radiation is the sum of Cherenkov and Smith–Purcell ones. The intensities of radiation from the dielectric pipe with periodic internal radius and with the constant one are compared. It is shown that the radiation from periodic internal structure may be several times more intensive than that from usual pipe with the smooth internal surface. Also, the spectral–angular distribution of radiation is shown to oscillate with the radius of the waveguide, both for periodically changed and for straight internal channel.

A linearized field theory of a grating-coupled Smith-Purcell traveling-wave tube (TWT) is presented. The configuration describes the propagation of a magnetized, sheet electron beam through a parallel-plate waveguide in which two opposing faces of the waveguide consists of either 1) a pair of identical diffraction gratings (referred to as a double-sided configuration) or 2) a diffraction grating along one face and a flat plate along the opposing face (referred to as a single-sided configuration). This is a two-dimensional formulation since we assume the configuration is uniform in the direction parallel to the slots in the grating. For each of these configurations, we derive the linearized dispersion equations for the vacuum structures and the wave-particle interaction in both the infinitely strong magnetic field limit and for an arbitrary (solenoidal) magnetic field. A discussion of the extraction efficiency based on phase-trapping arguments is also presented. An example of a W-band Smith-Purcell TWT is discussed.

THz emission spectra from a grating-coupled two-dimensional plasmon system driven by DC current are calculated in a self-consistent manner. The emission peaks show strong resonant enhancement due to Smith–Purcell effect.

A novel Smith-Purcell tunable radiation source with relativistic electron beam of middle energy and a quasi-optical resonator composed of diffraction grating and three-mirror reflector is reported. Theoretical analyses and numerical simulation results indicate that coherent radiation with peak power of a few MW order can be achieved from this experimental model. The typical curve of PIC simulation and cool testing experiment is also given.

The design considerations and the experimental steps for the realisation of a miniaturised free-electron laser, which uses the Smith–Purcell effect to generate THz-radiation, are presented. As an electron source a miniaturised field emitter cathode with integrated extractor and focusing optics is employed. Due to the very high brightness of this source an intensive portable and tuneable source for the near- and far-infrared is expected. Electron-beam-induced deposition and computer control is used to build the field electron emitter with an extractor and focusing lens on a prefabricated wiring pattern incorporating a metal line grating. This is a novel fabrication technique and allows us to build an extremely powerful miniaturised source. The field electron source with one single emitter delivers an emission current as high as 1 mA at 70 V extraction voltage and carries a current density of 20 MA/cm2 in the wire without being destroyed.

Smith-Purcell radiation from a charge running near a photonic crystal is calculated for a slab system of a periodic array of dielectric spheres, with the photonic band effect taken into account exactly. The radiation spectrum has a series of resonantly enhanced structures, which are shown to arise accompanying the excitation of the photonic bands. It is also shown that the overall intensity of the emission band does not depend very strongly on the slab thickness but the height of the resonant peaks increases progressively with thickness due to the enhanced Q value of excited photonic bands.

New results on field electron emitters built with electron beam induced deposition and a new application for such electron sources are presented. Electron beam induced deposition offers the possibility of building three-dimensional structures with very high resolution, thus allowing design of all kinds of electrical and optical micro- and nano-devices. Field electron emission experiments with emitters built with Pt and Au precursor materials were conducted. It could be shown that field emitters of this kind need less than 100 V for an emission current of more than 1 mA. The results are compared to those of former experiments which could be confirmed by this piece of work. As a new topic for the application of high power electron field emitters the concept of a miniaturised free electron laser is presented.

The Smith-Purcell radiation spectrum is calculated for the trajectory of a running charge parallel to the surface of a photonic crystal of dielectric spheres. Analysis is given for the dependence of the spectrum on the velocity of the running charge, the distance of the trajectory from the photonic crystal, and on the light absorption of the photonic crystal. It is shown that all the characteristic features of the radiation spectrum are satisfactorily explained by treating a direct light emitted by the charge as an incident light on the photonic crystal.

An experiment on a novel Smith–Purcell free electron laser (FEL) is described in this paper. The FEL is driven by a relativistic sheet electron beam of middle energy. The high frequency system of the device is a quasi-optical resonator composed of a diffraction grating and a three-mirror reflector. Coherent radiation with a peak power of tens of kW at the 3 mm waveband is sucessfully detected from an experimental facility. The main experimental parameters are: sheet beam energy from 400 kV to 500 kV; pulse length of voltage 70 ns; pulse beam current 0.2 kA; synchronous guide magnetic field up to 1.2 T with 10 ms pulse length; and grating period 2.2 mm.

The diffraction radiation (DR) has been considered at small emission angle in the optical and infrared region when a particle moves parallel and close to a conducting target consisting of the number of strips spaced by vacuum gaps. The maximum values of spectral–angular intensity distribution of DR is concentrated in the angular range comparable to γ −1 . The evolution of the spectral–angular distribution of DR intensity depending on the strip width and number of strips has been considered. The theoretical model to calculate the intensity of this radiation has been developed. On the basis of this model the spectra of resonant diffraction radiation (RDR) have been calculated for the Smith–Purcell geometry. The principal possibility of Smith–Purcell effect (SPE) experimental investigation in optical region has been shown. The comparison with undulator radiation (UR) has been carried out.

Frequency multiplication in the Smith-Purcell free electron laser (FEL) as a way to obtain powerful millimeter/ sub-millimeter stimulated radiation from a high-current, moderately relativistic electron beam is studied. It is shown that the main mechanism that provided the multiplication is mutual scattering of low-frequency and high-frequency waves on the electron beam. The use of this mechanism can provide the power level of tens of megawatts and the possibility of a relatively broadband (few percent) frequency tuning.

Realization of an effective single-mode oscillator based on the stimulated emission of radiation by relativistic electrons moving along a periodically corrugated waveguide, is theoretically shown to be possible in the regime, when the corrugation period is much larger than the operating wavelength.

A relativistic electron beam with velocity /spl nu//sub b/z passing over a metallic grating, with deep periodic depressions of wavenumber k/sub 0/z, excites a slow wave (/spl omega/, k/sub z/) via Cerenkov interaction, /spl omega/=(k/sub z/+k/sub 0/)/spl nu//sub b/. The beam bunches induce currents in the fins of the grating that act as a phased radiating dipole array, thereby generating coherent radiation at a wavelength /spl lambda/=(2/spl pi//k/sub 0/l)(c//spl nu//sub b/-sin/spl theta/) where l is an integer and /spl theta/ is the angle of emission measured from the normal of the grating. The current threshold for the instability and radiation power scaling with beam current are discussed.

The radiation of ultrarelativistic charged particle passing near a grating (Smith–Purcell radiation (SPR)) has been considered on the basis of a simple physical model, where SPR is treated as the resonant diffraction radiation (RDR). The apparent analogy between RDR and a well known resonant transition radiation has been used. The results have been compared with those obtained via other approaches. For an ultrarelativistic case it has been shown that the SPR intensity for a grating designed from strips separated by vacuum gaps sufficiently exceeds the one for traditional grating made up by a periodically deformed continuous surface.

A diffraction grating mounted in the electron beam focal region of a scanning electron microscope has been used to produce superradiant emission over the 300--900 $\ensuremath{\mu}\mathrm{m}$ wavelength range. Feedback is provided by the grating itself and the electron beam is focused and positioned over the grating by the microscope's electron optical system. Extensions of this technique promise a new tunable, coherent, cw source for the difficult to access far infrared (30--1000 $\ensuremath{\mu}\mathrm{m}$) range of the spectrum.

Smith-Purcell radiation is produced when a charged particle moves close and parallel to a diffraction grating. Calculation of Smith-Purcell spectra is therefore linked to a special grating problem, involving incident evanescent waves describing the field of the moving electron. For large period gratings, radiation in the far-infrared and millimetric range is produced, in a spectral range where metallic gratings can often be considered as infinitely conducting. In that case, conservation laws and a reciprocity theorem are derived for Smith-Purcell radiation by applying techniques from electromagnetic grating theory.

Absorption of a photon by an electron moving parallel to a rough surface is studied.In the weak scattering regime we have evaluated the absorption probability of absorption of a single photon. It is shown the absorption probability with diffusional contribution becomes large by a lin/l factor compared to the analogous result with the single scattering contribution. The maximum of probability takes place for the infrared wavelengths and strongly depends on the particle energy. We also discuss the case of two-dimensional periodical surface profile and indicate optimal conditions for maximal absorption probability. The results can be used in electron energy gain spectroscopy and in laser-driven acceleration., 5 pages,2 figures

The interaction processes of an electron beam with an external microwave field are studied in a quasioptical electronic device with distributed interaction using the Smith-Parcell effect. A distinctive feature of this device is an electrodynamic feedback loop in the form of an unstable two-mirror open resonator (OR) and two autonomous elements of microwave power input and output. Amplification modes are examined for different power levels of the external signal. It is shown that scenarios of electron beam dynamic parameter variation can be observed when the phase of the incident electromagnetic wave is changed. The measurements are carried out over a frequency range of 68 to 73 GHz.

In this paper, linear theory and 3 dimension numerical calculations (R.DRO) are reported, the operation complex frequency equation is given. The test is carried out on a dynamical model, theoretical and test results of R.DRO have been analysed.

We propose a novel room-temperature semiconductor source of narrowband coherent THz radiation that radiates via the Smith-Purcell effect and uses the Gunn effect to increase the radiated power (Figure 1). The radiation frequency of the device depends only on the grating period and the velocity of the Gunn domain, reaching low THz range with submicron grating. The Smith-Purcell effect is well-known in vacuum electronics and accelerator physics: a DC electron beam focused parallel to a metallic grating generates weak, incoherent electromagnetic radiation called spontaneous Smith-Purcell radiation (SPR). A bunched electron beam instead generates coherent stimulated SPR, with radiated power many orders of magnitude stronger than spontaneous SPR. Spontaneous SPR has been observed in semiconductors, but only at low temperature. The Gunn effect naturally provides space-charge bunching in semiconductors, and Gunn domains generate stimulated SPR at room temperature in the proposed devices. We develop a simple analytic model to describe the radiation which agrees well with device simulations. The small size of the radiative portion of the device suggests the use of an integrated antenna which significantly boosts the power of simulated devices. Our results indicate that the effect should be observable from a InP device, with power density of 30nW/μm of device width at 0.27 THz and 6nW/μm at 0.44THz. Results based on InN parameters look very promising for this approach with calculated power densities of 3.5μW/μm at 0.25THz, 20nW/μm at 1.0THz, and 3nW/μm at 2.0THz. We conclude that experimental investigation is warranted.

The Smith-Purcell radiation is usually measured when an electron passes over the grating of metallic stripes. However, for high frequencies (exceeding the plasma frequency of the grating material) none material could be treated as a conductor, but ought to be considered as a dielectric with plasma-like permittivity. So for describing Smith-Purcell radiation in the range of high frequencies new theoretical approaches are needed. In the present paper we apply the simple variant of eikonal approximation developed earlier to the case of radiation on the set of parallel semi-infinite dielectric plates. The formulae obtained describe the radiation generated by the particles both passing through the plates (traditionally referred as "transition radiation") and moving in vacuum over the grating formed by the edges of the plates (traditionally referred as "diffraction radiation", and, taking into account the periodicity of the plates arrangement, as Smith-Purcell radiation)., Submitted to Journal of Physics: Conference Series

Smith-Purcell (S-P) radiation is produced when electrons graze the surface of a grating. Calculations based on the theory of diffraction radiation show that, given severe restrictions on ${\mathit{e}}^{\mathrm{\ensuremath{-}}}$-beam quality, S-P radiation is highly efficient. Efficient S-P x-ray generation requires relativistic ${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ beams having a transverse momentum and dimension whose product approaches the Heisenberg uncertainty limit.

A few years ago, a new theory for producing coherent Smith-Purcell radiation from an initially continuous electron beam was proposed. It was 2-D, and it has been supported by particle-in-cell code simulations, although no experiments have, until now, provided confirmation. In fact, all experiments used a round beam, for which the 2-D theory may not be valid. We report here on a two-pronged attack on this problem. A 3-D simulation in the microwave domain indicates that coherent radiation, at a frequency near that of the 2-D simulation, should be produced. We are also preparing a demonstration experiment using an intense finite-width sheet beam to confirm the theory and simulations.

The Smith-Purcell radiation theory is created taking into account the electron beam self-modulation on the harmonics of the BWO mode at the self-consistent problem definition. The diffraction radiation field amplitudes for different rf current harmonics are retrieved depending on task parameters.

In a Smith–Purcell amplifier, the guiding magnetic field couples the TE and TM modes. However, for an incident TM wave it is shown that the scattered TM waves can be determined with the induced TE waves neglected, the latter being treated within a first‐order approximation. The response function of the amplifier for the TM waves is derived, and the dependence of its poles on the intensity of the guiding magnetic field is investigated. It is found that there are five poles, two of them complex, irrespective of the guiding field intensity and related to the ‘‘pure’’ slow‐wave‐structure poles; two other poles may be complex only if the cyclotron frequency is below a ‘‘cutoff’’ (determined explicitly) and resemble ‘‘gyrotron’’ poles. The cutoff is shown to be proportional to the shift (due to collective effects) in the radiation wave vector. The first pair of poles emerges from the longitudinal electronic oscillation, while the second pair corresponds to the transverse oscillation. The real pole into which the gyrotronlike poles degenerate is precisely the third pole, which occurs in slow‐wave structures under strong magnetic fields. By a suitable choice of the magnetic field a 10% increase is obtainable in the gain of the amplifier; this optimal field is determined and shown, within the relevant range of parameters, to be linear with the device length.

This paper reports the experimental results of the Smith–Purcell free-electron maser (orotron) developed at University of Electronic Science and Technology of China (UESTC). The output powers from this FEM are 200 and 1200 mw, respectively, at 3 and 4 mm wavelengths.

Smith-Purcell (SP) effect has been widely used for the generation of the millimeter to infrared wave radiation. The theoretical study and computer simulation on the SP radiation in a special kind of 3-mirror cavity with a grating on the inner surface, a cylindrical mirror, are given in the paper. The results show that it might be a good promising THz radiation source with kW CW power at room temperature.

A tunable terahertz source (TTS) based on a Smith-Purcell emitter will be described. The tunable THz source is analogous to low frequency electron beam devices such as magnetrons, backward wave oscillators and traveling wave tubes. The device offers continuous tunability, compactness, and robust operation. Examples of THz spectroscopy will be given.

We report the observation of enhanced coherent Smith-Purcell radiation (SPR) at terahertz (THz) frequencies from a train of picosecond bunches of 15 MeV electrons passing above a grating. SPR is more intense than other sources, such as transition radiation, by a factor of Ng, the number of grating periods. For electron bunches that are short compared with the radiation wavelength, coherent emission occurs, enhanced by a factor of Ne, the number of electrons in the bunch. The electron beam consists of a train of Nb bunches, giving an energy density spectrum restricted to harmonics of the 17 GHz bunch train frequency, with an increased energy density at these frequencies by a factor of Nb. We report the first observation of SPR displaying all three of these enhancements, NgNeNb. This powerful SPR THz radiation can be detected with a high signal to noise ratio by a heterodyne receiver.

In the present work in-self-consistent setting of the potentiality of electromagnetic oscillation excitation in a distributed semiconductor structure on Smith-Purcell (diffraction radiation) effect is considered. Thus the electrodynamic analysis of interaction of charge carriers in semiconductor drifting flow with field of periodic wave leading structure on Smith-Purcell effect is studied. The electrodynamic model of distributed semiconductor structure is the wave guide that consists of infinite conducted shields, one of which is diffraction grating.

The inverse Smith–Purcell effect is a candidate for laser‐driven linacs utilizing the interaction between laser light and an electron beam traveling just in front of a metallic grating. We have performed experiments to study electron energy spread as a function of electron beam position above the grating. A submillimeter wave laser (CH3F, 496 μm) is used as a driving source. It is found that the energy spread characteristics show exponential decay of the interaction strength (field intensity) in the direction perpendicular to the grating surface, as a classical theory on the effect predicts.

This paper presents the efficiency of Smith-Purcell (SP) radiation generation for lamellar and triangular metal gratings(MG) in H-polarization. The efficiency was calculated by the modal expansion method for lamellar MG and the improvedpoint matching method for thangular MG, respectively. Most important MG parameters involved in the calculation were:the space period, the total number of grooves, the profile and the shape of the groove, and the geometry of the reflectingsurface. Calculations were performed for relativistic electron beams (REB) with energies in 1 — 50 MeV domains. Theemission angle of coherent SP radiation depending on MG and REB parameters is also presented.Keywords: Metal grating efficiency, Smith-Purcell radiation 1. INTRODUCTION An electron moving near a metal grating emits Smith-Purcell radiation. The relation below gives the wavelength of the SPphoton: =1.[isinJ. (1) in which 3 = v I c is the ratio of the velocity v of electrons to the light velocity c in vacuum, 2g

Electrons moving above a metal grating emit evanescent waves as well as Smith–Purcell radiation. We used a mode-expansion method for analyzing evanescent modes in the optical region. The results calculated in the mode-expansion method were compared to those simulated by a finite-difference time-domain numerical method. Good agreement between the two methods was obtained.