Electrodynamics of Media

Contains reports on one research project.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U. S. Air Force) under Contract DAAB07-71-C-0300U. S. Air Force Cambridge Research Laboratories Contract F19628-70-C-006

Electrodynamics of Media

Contains reports on two research projects.Joint Services Electronics Programs (U.S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E

Electrodynamics of Media

Contains research objectives and reports on one research project.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E

Solvable glassy system: static versus dynamical transition

A directed polymer is considered on a flat substrate with randomly located parallel ridges. It prefers to lie inside wide regions between the ridges. When the transversel width $W=\exp(\lambda L^{1/3})$ is exponential in the longitudinal length $L$, there can be a large number $\sim \exp L^{1/3}$ of available wide states. This ``complexity'' causes a phase transition from a high temperature phase where the polymer lies in the widest lane, to a glassy low temperature phase where it lies in one of many narrower lanes. Starting from a uniform initial distribution of independent polymers, equilibration up to some exponential time scale induces a sharp dynamical transition. When the temperature is slowly increased with time, this occurs at a tunable temperature. There is an asymmetry between cooling and heating. The structure of phase space in the low temperature non-equilibrium glassy phase is of a one-level tree.Comment: 4 pages revte

Efficient low-power terahertz generation via on-chip triply-resonant nonlinear frequency mixing

Achieving efficient terahertz (THz) generation using compact turn-key sources operating at room temperature and modest power levels represents one of the critical challeges that must be overcome to realize truly practical applications based on THz. Up to now, the most efficient approaches to THz generation at room temperature -- relying mainly on optical rectification schemes -- require intricate phase-matching set-ups and powerful lasers. Here we show how the unique light-confining properties of triply-resonant photonic resonators can be tailored to enable dramatic enhancements of the conversion efficiency of THz generation via nonlinear frequency down-conversion processes. We predict that this approach can be used to reduce up to three orders of magnitude the pump powers required to reach quantum-limited conversion efficiency of THz generation in nonlinear optical material systems. Furthermore, we propose a realistic design readily accesible experimentally, both for fabrication and demonstration of optimal THz conversion efficiency at sub-W power levels

Electrodynamics of Media

Contains research objectives, summary of research and reports on two research projects.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DAAB07-71-C-0300U. S. Army Research Office - Durham (Contract l)AHC04-72-C-0044)California Institute of Technology Contract 953524M.I.T. Sloan Fund for Basic Researc

Second Harmonic Generation for a Dilute Suspension of Coated Particles

We derive an expression for the effective second-harmonic coefficient of a dilute suspension of coated spherical particles. It is assumed that the coating material, but not the core or the host, has a nonlinear susceptibility for second-harmonic generation (SHG). The resulting compact expression shows the various factors affecting the effective SHG coefficient. The effective SHG per unit volume of nonlinear coating material is found to be greatly enhanced at certain frequencies, corresponding to the surface plasmon resonance of the coated particles. Similar expression is also derived for a dilute suspension of coated discs. For coating materials with third-harmonic (THG) coefficient, results for the effective THG coefficients are given for the cases of coated particles and coated discs.Comment: 11 pages, 3 figures; accepted for publication in Phys. Rev.

Locating the minimum : Approach to equilibrium in a disordered, symmetric zero range process

We consider the dynamics of the disordered, one-dimensional, symmetric zero range process in which a particle from an occupied site $k$ hops to its nearest neighbour with a quenched rate $w(k)$. These rates are chosen randomly from the probability distribution $f(w) \sim (w-c)^{n}$, where $c$ is the lower cutoff. For $n > 0$, this model is known to exhibit a phase transition in the steady state from a low density phase with a finite number of particles at each site to a high density aggregate phase in which the site with the lowest hopping rate supports an infinite number of particles. In the latter case, it is interesting to ask how the system locates the site with globally minimum rate. We use an argument based on local equilibrium, supported by Monte Carlo simulations, to describe the approach to the steady state. We find that at large enough time, the mass transport in the regions with a smooth density profile is described by a diffusion equation with site-dependent rates, while the isolated points where the mass distribution is singular act as the boundaries of these regions. Our argument implies that the relaxation time scales with the system size $L$ as $L^{z}$ with $z=2+1/(n+1)$ for $n > 1$ and suggests a different behaviour for $n < 1$.Comment: Revtex, 7 pages including 3 figures. Submitted to Pramana -- special issue on mesoscopic and disordered system