Benchmark of FEM, Waveguide and FDTD Algorithms for Rigorous Mask Simulation

An extremely fast time-harmonic finite element solver developed for the transmission analysis of photonic crystals was applied to mask simulation problems. The applicability was proven by examining a set of typical problems and by a benchmarking against two established methods (FDTD and a differential method) and an analytical example. The new finite element approach was up to 100 times faster than the competing approaches for moderate target accuracies, and it was the only method which allowed to reach high target accuracies.Comment: 12 pages, 8 figures (see original publication for images with a better resolution

Plasma instability and amplification of electromagnetic waves in low-dimensional electron systems

A general electrodynamic theory of a grating coupled two dimensional electron system (2DES) is developed. The 2DES is treated quantum mechanically, the grating is considered as a periodic system of thin metal strips or as an array of quantum wires, and the interaction of collective (plasma) excitations in the system with electromagnetic field is treated within the classical electrodynamics. It is assumed that a dc current flows in the 2DES. We consider a propagation of an electromagnetic wave through the structure, and obtain analytic dependencies of the transmission, reflection, absorption and emission coefficients on the frequency of light, drift velocity of 2D electrons, and other physical and geometrical parameters of the system. If the drift velocity of 2D electrons exceeds a threshold value, a current-driven plasma instability is developed in the system, and an incident far infrared radiation is amplified. We show that in the structure with a quantum wire grating the threshold velocity of the amplification can be essentially reduced, as compared to the commonly employed metal grating, down to experimentally achievable values. Physically this is due to a considerable enhancement of the grating coupler efficiency because of the resonant interaction of plasma modes in the 2DES and in the grating. We show that tunable far infrared emitters, amplifiers and generators can thus be created at realistic parameters of modern semiconductor heterostructures.Comment: 28 pages, 15 figures, submitted to Phys. Rev.

Driven Diffusive Systems: An Introduction and Recent Developments

Nonequilibrium steady states in driven diffusive systems exhibit many features which are surprising or counterintuitive, given our experience with equilibrium systems. We introduce the prototype model and review its unusual behavior in different temperature regimes, from both a simulational and analytic view point. We then present some recent work, focusing on the phase diagrams of driven bi-layer systems and two-species lattice gases. Several unresolved puzzles are posed.Comment: 25 pages, 5 figures, to appear in Physics Reports vol. 299, June 199

Fast start of oscillations in a short-pulse relativistic magnetron driven by a transparent cathode.

The magnetron has been a major component of radar systems since its introduction in World War II. The newer radar techniques require high peak power (GW) and short microwave pulses (few ns). To serve as a microwave source for short-pulse applications it is imperative that the magnetron needs to have both fast start and fast rate of build-up of oscillations. Both of these factors are contingent on the cathode geometry. The transparent cathode was invented at the University of New Mexico in an endeavor to improve the start time and increase the rate of build-up of oscillations in short-pulse relativistic magnetrons. The construction of the transparent cathode involves the removal of longitudinal strips of material from a hollow cathode. The resultant geometry has manifold advantages the first and the foremost of which is that it makes the cathode transparent to E_theta, thereby greatly increasing its amplitude where electrons are emitted. Hence one would expect faster rate of build-up of oscillations. Secondly, this geometry simultaneously gives rise to several different forms of priming: cathode priming, electrostatic priming and magnetic priming. The number of cathode strips is chosen so that it would excite a particular mode of interest (e.g. 6 strips would favor the formation of 6 spokes). The cathode strips may be oriented azimuthally in a manner that the electron bunches from the cathode strips would be released into the favorable phase of the mode of interest where efficient exchange of energy between the electrons and the RF fields could take place. The highlights of this dissertation are proof-of-concept computer simulations demonstrating the benefits of the transparent cathode in an A6 magnetron driven by a transparent cathode that have validated the simulations

One-point functions in massive integrable QFT with boundaries

We consider the expectation value of a local operator on a strip with non-trivial boundaries in 1+1 dimensional massive integrable QFT. Using finite volume regularisation in the crossed channel and extending the boundary state formalism to the finite volume case we give a series expansion for the one-point function in terms of the exact form factors of the theory. The truncated series is compared with the numerical results of the truncated conformal space approach in the scaling Lee-Yang model. We discuss the relevance of our results to quantum quench problems.Comment: 43 pages, 20 figures, v2: typos correcte