Characterization of Optical Emission Mechanism Utilizing Traveling Electron Beam on a Waveguide

The mechanism of optical emission from a high-refractive-index waveguide excited by a traveling electron beam was quantitatively investigated. The wavelength of optical emission was 1.5$\ \mu$m at an electron acceleration voltage of approximately 40$~$kV. This optical emission is understood to be a type of Cherenkov radiation. However, the dynamics of each electron were analyzed on the basis of quantum mechanical treatment, where an electron is expressed as a spatially spreading wave not as a spatially localized point particle. In this analytical model, several key parameters have been introduced such as coefficient to include the spontaneous emission, a coupling coefficient between the electron beam and the optical field, the coherent length of the electron wave, and the relaxation time of the electron wave. Numerical values of these parameters were evaluated systematically by comparing the results of theoretical analyses with experimentally measured data of the optical power, the optical spectrum, and the spatial distribution of electron density.