帕维亚大学Scott博士和南洋理工大学YangjieLiu作学术报告

来自意大利帕维亚大学（University of Pavia, Italy）Scott James Robertson博士和新加坡南洋理工大学（Nanyang Technological University Singapore）Yangjie Liu在访问光及电磁波研究中心期间，于7月11日下午为分别全院师生作了题为《Quasi-normal mode description of the optical response》与《Time-varying emission of electrons and its relevant EM phenomenon》的学术报告。

报告信息如下：

Speaker: Dr. Scott James Robertson, University of Pavia, Italy

Title: Quasi-normal mode description of the optical response

Abstract: Many interesting features of the optical response of dielectric structures can be formulated in terms of resonances.  Remarkably, under quite general conditions, this resonance-based description is complete: the optical response of a system can be formulated entirely in terms of its quasi-normal modes, which are exact solutions of Maxwell's equations given outgoing boundary conditions.  These quasi-normal modes are analogous to quantum mechanical eigenstates -- in particular, they admit a perturbation theory under small deformations of the structure.  I will show how this description is accomplished, and how it can be used to describe observable properties such as reflection, transmission and absorption spectra for dielectric structures with a suitably small perturbation.

Speaker: Yangjie Liu, Nanyang Technological University Singapore

Title: TIME-VARYING EMISSION OF ELECTRONS AND ITS RELEVANT EM PHENOMENON

Abstract: We try to consider two aspects of electron emission scenario: one on increasing electron emission counts by injecting time-varying electron flow under short-pulse condition and the other on induced electromagnetic fields by electron flow within space.

(1). Time-varying profile of injection electron flow from cathode side offers possibilities to transcend conventional time-uniform space-charge limit under short- pulse condition, and monotonously increasing functions of time-profile could be such a case. A laser- excited emission mechanism is computationally introduced here, illustrating that for ultrahigh laser field space charge effect becomes notable and electric DC field can be an efficient parameter to tune the space-charge limit. Particle-In-Cell(PIC) simulation is also performed to demonstrate agreement with home-made calculation methods.

(2). Another phenomenon related to electron flow is that evanescent wave produced by mechanical motion of electron bunch can be accumulated under certain artificial circumstances, inhomogeneous or anisotropic space (realizable in metamaterial) such as Maxwell’s fisheye structure. Other than the former electrostatics problem, electrodynamics has to be formulated to derive solution in frequency domain from vector Helmholtz equation. Dyadic Green’s function and method of scattering superposition are chosen to give analytic electromagnetic field solution for transition radiation from Maxwell’s fisheye. This calculation may pave the way to investigate novel scheme of brand band light source, transferring energy from electron’s kinetic one to radiation.