Optical emission from a high-refractive-index waveguide excited by a traveling electron beam

Abstract

An optical emission scheme was demonstrated, in which a high-refractive-index waveguide is excited by a traveling electron beam in a vacuum environment. The waveguide was made of Si-SiO 2 layers. The velocity of light propagating in the waveguide was slowed down to 1/3 of that in free space due to the high refractive index of Si. The light penetrated partly into the vacuum in the form of a surface wave. The electron beam was emitted from an electron gun and propagated along the surface of the waveguide. When the velocity of the electron coincided with that of the light, optical emission was observed. This emission is a type of Cherenkov radiation and is not conventional cathode luminescence from the waveguide materials because Si and SiO 2 are transparent to light at the emitted wavelength. This type of emission was observed in an optical wavelength range from 1.2 to 1.6 m with an electron acceleration voltage of 32-42 kV. The characteristics of the emitted light, such as the polarization direction and the relation between the acceleration voltage of the electron beam and the optical wavelength, coincided well with the theoretical results. The coherent length of an electron wave in the vacuum was confirmed to be equal to the electron spacing, as found by measuring the spectral profile of the emitted light.

Criterion of applicable models for planar type Cherenkov laser based on quantum mechanical treatments

“…In these analyses [16,17], the electron is represented to be spatially spreading wave, and experimentally observed the optical emission with the electron acceleration voltage of around 40 kV [18]. We also estimated the spreading length of an electron wave in our experiment to be 20 to 40 m μ by comparing the experimentally obtained emission profile with theoretical analysis [18,19].…”

“…We also estimated the spreading length of an electron wave in our experiment to be 20 to 40 m μ by comparing the experimentally obtained emission profile with theoretical analysis [18,19].…”

Analysis of saturation phenomena in Cerenkov free-electron lasers with a planar waveguide

“…It is worth to note that the saturation effect is even included in the linear gain coefficient g 1 , whereas the relative electron phase XðzÞ varies spatially due to the variation of the average velocity given by Eq. (20).…”

“…[16][17][18][19][20][21] In the CFEL, an electron beam moves along a surface of a dielectric medium by which the propagating velocity of an electromagnetic wave (EM-wave) is slowed down. The electron beam can transfer its energy to the EM wave when the electron beam velocity matches with the phase velocity of the EM wave.…”

Unified analysis for calculating the amplification gain of Cerenkov laser in the single-particle and collective regimes

“…5 It is assumed that the EM wave can interact only with the space-charge wave when the phase velocities of these waves become equal, and the EM wave satisfies the dispersion relation for the waveguide. 5 On the basis of classical 9,10 and quantum [11][12][13] approaches, the authors have shown that due to the asymmetric separations between electrons accompanied with the beam bunching, the asymmetric Coulomb forces exerted on an electron by the neighboring electrons work to recover its initial position. Therefore, the unbalanced Coulomb forces work to weaken (relax) the bunching mechanism.…”