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Free electrons passing along the surface of the grating produce a stimulated emission, referred to as the Smith-Purcell (SP) effect. Here we firstly report theoretically evidence of the inverse Smith-Purcell effect at about 300GHz (ISP) by loading the specially designed photonic crystals (PCs) with negative refractive on a slits structure, which could provide a new idea for coherent Smith-Purcell. The inverse Smith-Purcell effect reflect that with the observation moving from the front to the rear, the observation frequency change first from the intermediate frequency to the high frequency, and then from the low frequency to the intermediate frequency, which is different from the normal SP. The proposed ISP is of great significance for obtaining power enhanced, coherent and tunable terahertz radiation.

In this paper, we numerically investigate on a three dimensional Smith-Purcell (SP) based terahertz frequency multiplier. Frequency multiplication procedure is proposed via learning of spontaneous SP radiation. At low frequency regions, texturing the metallic surfaces would manipulate the spoof surface plasmons (SSPs). Due to electronically exciting of these SSPs in a one-dimensionally extended metallic grating, a strong electron-plasmon momentum coupling develops and electron bunches arise. The evanescent wave releases from both ends of the structure. At the frequency harmonics of these SSPs, an umklapp process redshifts the SSP momentum beyond the light zone and the SP radiation is generated in the span of 0.466–1.1 THz and detected with a maximum peak around 90° (with respect to the grating). The SP radiation center frequency is ~0.65 THz. Three dimensional particle-in-cell (PIC) simulations have been performed via finite integral method and the obtained results completely agree with analytic ones.

Smith-Purcell radiation is usually detected at the motion of an electron above a grating of metal strips. However, for high frequencies (exceeding the plasma frequency of the grating material) no substance can be considered a conductor, but instead should be considered a dielectric with plasma-type permeability. Therefore, new approaches are required to describe the Smith-Purcell radiation in the high frequency range. In this article a previously developed variant of eikonal approximation is applied for description of the radiation on a set of parallel semi-infinite plates. The derived equations describe the radiation generated both by the particles passing across the plates (usually referred to as “transition radiation”) and by the particles traveling above the grating formed by the edges of the plates (usually referred to as “diffraction radiation,” or, taking into account the periodicity of the grating, as the Smith-Purcell radiation).

Dielectric laser acceleration exploiting the large optical field strength of short laser pulses and the proximity of a dielectric structure can support high acceleration gradients may therefore lead to much smaller accelerators, with future potential application in table-top free electron lasers. We report a proof-of-concept experiment demonstrating dielectric laser acceleration of non-relativistic 28 keV electrons derived from a conventional scanning electron microscope column at a single fused-silica grating. The electrons pass the grating as closely as 50 nm and interact with the third spatial harmonic, which is excited by 110 fs long 800 nm laser pulses with a peak electric field of 2.85 GV/m. The observed maximum acceleration gradient of 25 MeV/m is already comparable to state-of-the-art radio-frequency structures. This work thus represents a demonstration of scalable laser acceleration and of the inverse Smith–Purcell effect in the optical regime. For relativistic electrons and otherwise identical conditions up to two orders of magnitude larger acceleration gradients are expected.

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

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.

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.

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.

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.

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.

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 (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.

An approach has been developed where the Smith-Purcell radiation (SPR), i.e. emission of electrons moving close to a periodic structure, is treated as the resonant diffraction radiation. Simple formulas have been designed for the SPR intensity for a grating having perfectly conducting strips spaced by a vacuum gap. The results have been compared with those obtained via other techniques. It has been shown that the intensity of radiation for the said gratings for a relativistic case sufficiently exceeds the SPR intensity for the grating made up by a periodically deformed continuous surface., 9 pages, LATEX, 3 Postscript figures, uses epsf.sty, submitted to Phys.Letters A

A beam of 3.6-MeV electrons has been used to study the generation of radiation in the far infrared (FIR) by the Smith-Purcell mechanism. The dependence of wavelength on angle of emission, over angles from 56\ifmmode^\circ\else\textdegree\fi{} to 150\ifmmode^\circ\else\textdegree\fi{} and wavelengths from 350 to 1860 \ensuremath{\mu}m, is in excellent agreement with the Smith-Purcell dispersion relation. Comparison of the yield with that from a 5000-K source suggests that the spontaneous Smith-Purcell effect offers an easily tunable alternative to the synchrotron as a coherent FIR source, and that it could also form the basis of an inexpensive, compact free-electron laser.

The theory of linear and stimulated free‐electron lasers using the Smith‐Purcell effect is presented. These lasers depend upon the resonant interaction of an electron beam with the longitudinal field of a surface‐harmonic wave on a diffraction grating. Detailed design criteria for the linear Smith‐Purcell‐effect laser are determined. Numerical estimates show that infrared lasers are feasible at beam currents smaller than 1 A and that single‐mode operation may be achieved. Saturation estimates determine the power output in the range 102 W. An expression for the gain of the stimulated Smith‐Purcell laser is derived. The frequency up‐conversion factor for the stimulated interaction may be very large. Its possible use as a soft x‐ray laser is limited by the available intensity of the pump wave.

We have observed for the first time the Smith-Purcell effect in GaAs-GaAlAs-heterostructures. A grating structure induces far infrared (FIR) emission from drifted carrier distributions, which is angle dependent and allows the determination of intrinsic carrier properties.

It is shown that energy can be injected into only one negative transmitted spectral order when the incident angle of the impinging light beam and the refractive indices of the lossless dielectric bounding media satisfy the condition of total reflection. This signifies that non-redundant scanning of Smith-Purcell radiation generated on one side of a periodic structure can be obtained by varying the velocity of the electron beam on the other side of the structure.

A rigorous solution is derived for the problem of radiation of the Smith–Purcell type (Smith and Purcell 1953) extracted from a radio-frequency bunched electric-current sheath, above a plane exhibiting a periodically varying surface reactance. The plane is regarded as a model of an optical reflection grating. The solution indicates that the presence of the grating will give rise to electromagnetic resonance effects which are closely related to the so-called Wood anomalies (Wood 1935; Twersky 1956; Hessel 1960; Hessel and Oliner 1962; Stewart and Gallaway 1962), encountered in optical-grating spectroscopy. Utilization of these resonances may be advantageous in the generation of millimeter waves.

We study here the gain of an amplifier based on the Smith–Purcell effect. The grating is characterized by a reflection matrix and the gain, in the exponential region, is calculated as a function of the beam height and thickness.

Interest in the development of laser-driven linacs has been stimu-lated recently by the advent of the high-power lasers. The use of a laser to accelerate charged particles was first proposed by K. Shimoda in 19621. He noticed that high values of acceleration per metre (acceleration gradient) could be obtained with an intense electric field in the output of a high-power laser. The inverse Smith–Purcell (ISP) effect proposed by us2 is a candidate for laser-driven linacs with a metallic grating as an interaction circuit. In 1953 Smith and Purcell demonstrated that light is emitted when a high-voltage electron beam moves parallel and close to a metallic optical diffraction grating in a direction perpendicular to the grating rulings3. The dispersion relationship is a synchronous condition between the electrons and the wave on the grating. Therefore, the inverse Smith-Purcell effect (ISP), or the extended interaction between electrons and an incident light wave should occur when the same relation is satisfied between the electrons and the incident wave (Fig. 1)2. Lawson pointed out4 that this effect would fail to accelerate relativistic particles. This difficulty was solved by Palmer5, who showed that acceleration is possible either if the particles travel skew to the grating lines, or if the radiation is falling at a skew angle onto the grating. Several authors have described possibilities for producing a grating linac (ISP effect) with accelerating field of a few GeV m−1 in the infrared or optical wave region6. Here we report the first observational evidence for this effect using a submillimetre-wave laser as a driving source. The experimental results give good agreement with theoretical predictions.

The inverse Smith-Purcell effect, which is one of the candidates for laser-driven linacs with a metallic grating as an interaction circuit to produce acceleration gradient of a few GeV/m, has first been demonstrated since its proposal in 1975. In this paper, we describe the theoretical analyses on this effect and also its first experimental evidence by using a submillimeter-wave laser as a driving source. The experimental results give good agreement with the theoretical predictions.

The orotron [1], ledatron [2], and diffraction radiation generator [3] are electron-tube devices that generate millimeter and submillimeter wave radiation by means of the Smith-Purcell effect. We have shown [4] that these devices are special cases of a general class of Smith-Purcell free-electron lasers considered by Wachtel [5]. The essential difference between these Smith-Purcell lasers and other free-electron lasers [6] is that in the former the electrons are bunched by a longitudinal rf electric field but in the latter they are bunched by a transverse magnetic field.

We have observed the inverse Smith-Purcell (ISP) effect for the first time by using a submillimeter wave laser as a driving source. The ISP effect is one of the candidates for laser-driven linacs with a metallic grating as an interaction circuit to produce acceleration gradient of a few GeV/m. In this paper, we describe our experimental apparatus including newly developed CO 2 laser and the first experimental evidence of this effect.

In this paper, we present a three dimensional numerical study on a terahertz frequency multiplier. The process of frequency multiplication is proposed via study of spontaneous Smith-Purcell (SP) radiation. Through introducing a single electron bunch perturbation which is passing over above a metallic grating, and due to interaction of electron bunch with surface wave, the evanescent wave radiates from the ends of the grating and the SP radiation is generated in the span of 0.466∼1.1 THz. We found that the maximum of SP radiation amplitude is distributed around 90° with the centre frequency 0f ∼0.65 THz. Simulations on the generation of SP radiation at THz frequencies have been performed with the help of the 3D particle-in-cell (PIC) finite integral method and results agree very well with analytic ones.

The inverse Smith-Purcell effect was observed to verify the theoretical predictions for the dependence of the size of the interaction space on the laser wavelength. Two submillimeter wave lasers with wavelengths of 184.6 mu m and 496 mu m were used as the driving lasers. It was found that the interaction strength for the driving laser with shorter wavelength decays more rapidly than that for the longer wavelength driving laser, as is predicted by theory. Measured decay constants of the field intensity have shown good agreement with theoretical values. >

The inverse Smith-Purcell effect is theoretically investigated in the submillimeter wave region for planning experiments. The effect in which coherent light waves interact with charged particles resonantly through a diffraction grating is one of the candidates for laser-driven linacs. The optimum grating dimensions with a rectangular groove profile are designed by analyzing the fields just in front of the grating surface. The energy spreads of the electrons resulting from interactions with the laser field were evaluated by computer simulations. It can be seen from the simulations that a laser power of 1 W can produce ∼ 30 eV increase in the electron energy spectrum.