Cyclotron resonance gain in the presence of collisions

Abstract

The conditions needed for the amplication of radiation by an ensemble of

magnetized, relativistic electrons that are collisionally slowing down are investigated.

The current study is aimed at extending the work of other researchers in developing

solid-state sources of Terahertz radiation. The source type considered here is based

on gyrotron-like dynamics of graphene electrons, or it can alternately be viewed

as a solid state laser source that uses Landau levels as its band structure and is

thus similar to a quantum cascade laser. Such sources are appealing because they

oer the potential for a compact, tunable source of Terahertz radiation that could

have commercial applications in scanning, communication, or energy transfer. An

exploration is undertaken, using linear and nonlinear theories, of the conditions

under which such sources might be viable, assuming realistic parameters. Classical

physics is used, and the model involves electrons in monolayer graphene assumed to

be pumped by a laser, follow classical laws of motion with the dissipation represented

by a damping force term, and lose energy to the electromagnetic eld as well. The

graphene is assumed to be in a homogeneous magnetic eld, and is sandwiched

between two partially-transmissive mirrors so that the device acts as an oscillator.

This thesis incorporates the results of two approaches to the study of the

problem. In the rst approach, a linear model is derived semi-analytically, which is

relevant to the conditions under which there is gain in the device and thus stable

operation is possible, versus the regime in which there is no net gain. In the second

approach, a numerical simulation is employed to explore the nonlinear regime and

saturation behavior of the oscillator. The simulation and the linear model both

assume the same original equations of motion for the eld and particles that interact

self-consistently. The model used here is very simplied, but the aim here is to

elucidate the basic principles and scaling behavior of such devices, not necessarily to

calculate what the exact dynamics, outputs, and parameters of a fully commercially

realized device will be.