Coulomb drag in the mesoscopic regime

We present a theory for Coulomb drag between two mesoscopic systems which expresses the drag in terms of scattering matrices and wave functions. The formalism can be applied to both ballistic and disordered systems and the consequences can be studied either by numerical simulations or analytic means such as perturbation theory or random matrix theory. The physics of Coulomb drag in the mesoscopic regime is very different from Coulomb drag between extended electron systems. In the mesoscopic regime we in general find fluctuations of the drag comparable to the mean value. Examples are the vanishing average drag for chaotic 2D-systems and the dominating fluctuations of drag between quasi-ballistic wires with almost ideal transmission.Comment: 4 pages including 2 figures. Proceedings of 19NSM, to apear in Phys. Script

Comment on "Pinched Flow Fractionation: Continuous Size Separation of Particles Utilizing a Laminar Flow Profile in a Pinched Microchannel"

[First paragraph] In a recent paper Yamada et al. propose the novel concept of "pinched flow fractionation" (PFF) for the continuous size separation and analysis of particles in microfabricated lab-on-a-chip devices. In their description of the basic principle they claim that especially the width of the pinched and broadened segments will affect theseparation performance. In the following we comment on the physics behind this statement.Comment: Comment on paper by Yamada et al. [Anal. Chem. 76(18), 5465 - 5471 (2004)]. Accepted for Anal. Che

Calculation of optical-waveguide grating characteristics using Green's functions and the Dyson's equation

We present a method for calculating the transmission spectra, dispersion, and time delay characteristics of optical-waveguide gratings based on Green's functions and Dyson's equation. Starting from the wave equation for transverse electric modes we show that the method can solve exactly both the problems of coupling of counter-propagating waves (Bragg gratings) and co-propagating waves (long-period gratings). In both cases the method applies for gratings with arbitrary dielectric modulation, including all kinds of chirp and apodisation and possibly also imperfections in the dielectric modulation profile of the grating. Numerically, the method scales as O(N) where N is the number of points used to discretize the grating along the propagation axis. We consider optical fiber gratings although the method applies to all 1D optical waveguide gratings including high-index contrast gratings and 1D photonic crystals.Comment: 16 pages including 16 figure

Stimulated plasmon polariton scattering

The plasmon and phonon polaritons of two-dimensional (2d) and van-der-Waals materials have recently gained substantial interest. Unfortunately, they are notoriously hard to observe in linear response because of their strong confinement, low frequency and longitudinal mode symmetry. Here, we propose a fundamentally new approach of harnessing nonlinear resonant scattering that we call stimulated plasmon polariton scattering (SPPS) in analogy to the opto-acoustic stimulated Brillouin scattering (SBS). We show that SPS allows to excite, amplify and detect 2d plasmon and phonon polaritons all across the THz-range while requiring only optical components in the near-IR or visible range. We present a coupled-mode theory framework for SPS and based on this find that SPS power gains exceed the very top gains observed in on-chip SBS by at least an order of magnitude. This opens exciting new possibilities to fundamental studies of 2d materials and will help closing the THz gap in spectrocopy and information technology.Comment: 7 pages, 3 figure

Proposal of highly sensitive optofluidic sensors based on dispersive photonic crystal waveguides

Optofluidic sensors based on highly dispersive two-dimensional photonic crystal waveguides are theoretically studied. Results show that these structures are strongly sensitive to the refractive index of the infiltrated liquid (nl), which is used to tune dispersion of the photonic crystal waveguide. Waveguide mode-gap edge shifts about 1.2 nm for dnl=0.002. The shifts can be explained well by band structure theory combined with first-order perturbation theory. These devices are potentially interesting for chemical sensing applications.Comment: 8 pages including 3 figures. Accepted for proceedings of Nanometa to appear in J. Opt. A: Pure Appl. Op

Hollow-core infrared fiber incorporating metal-wire metamaterial

Infrared (IR) light is considered important for short-range wireless communication, thermal sensing, spectroscopy, material processing, medical surgery, astronomy etc. However, IR light is in general much harder to transport than optical light or microwave radiation. Existing hollow-core IR waveguides usually use a layer of metallic coating on the inner wall of the waveguide. Such a metallic layer, though reflective, still absorbs guided light significantly due to its finite Ohmic loss, especially for transverse-magnetic (TM) light. In this paper, we show that metal-wire based metamaterials may serve as an efficient TM reflector, reducing propagation loss of the TM mode by two orders of magnitude. By further imposing a conventional metal cladding layer, which reflects specifically transverse-electric (TE) light, we can potentially obtain a low-loss hollow-core fiber. Simulations confirm that loss values for several low-order modes are comparable to the best results reported so far.Comment: REVTeX, just over 9 page

Photonic crystal fiber design based on the V-parameter

Based on a recent formulation of the V-parameter of a photonic crystal fiber we provide numerically based empirical expressions for this quantity only dependent on the two structural parameters - the air hole diameter and the hole-to-hole center spacing. Based on the unique relation between the V-parameter and the equivalent mode field radius we identify how the parameter space for these fibers is restricted in order for the fibers to remain single mode while still having a guided mode confined to the core region.Comment: 6 pages including 5 figures. Accepted for Optics Expres

Plasmonics for emerging quantum technologies

Expanding the frontiers of information processing technologies and, in particular, computing with ever increasing speed and capacity has long been recognized an important societal challenge, calling for the development of the next generation of quantum technologies. With its potential to exponentially increase computing power, quantum computing opens up possibilities to carry out calculations that ordinary computers could not finish in the lifetime of the Universe, while optical communications based on quantum cryptography become completely secure. At the same time, the emergence of Big Data and the ever increasing demands of miniaturization and energy saving technologies bring about additional fundamental problems and technological challenges to be addressed in scientific disciplines dealing with light-matter interactions. In this context, quantum plasmonics represents one of the most promising and fundamental research directions and, indeed, the only one that enables ultimate miniaturization of photonic components for quantum optics when being taken to extreme limits in light-matter interactions.Comment: To appear in Nanophotonic

How nonlocal damping reduces plasmon-enhanced fluorescence in ultranarrow gaps

The nonclassical modification of plasmon-assisted fluorescence enhancement is theoretically explored by placing two-level dipole emitters at the narrow gaps encountered in canonical plasmonic architectures, namely dimers and trimers of different metallic nanoparticles. Through detailed simulations, in comparison with appropriate analytical modelling, it is shown that within classical electrodynamics, and for the reduced separations explored here, fluorescence enhancement factors of the order of $10^{5}$ can be achieved, with a divergent behaviour as the particle touching regime is approached. This remarkable prediction is mainly governed by the dramatic increase in excitation rate triggered by the corresponding field enhancement inside the gaps. Nevertheless, once nonclassical corrections are included, the amplification factors decrease by up to two orders of magnitude and a saturation regime for narrower gaps is reached. These nonclassical limitations are demonstrated by simulations based on the generalised nonlocal optical response theory, which accounts in an efficient way not only for nonlocal screening, but also for the enhanced Landau damping near the metal surface. A simple strategy to introduce nonlocal corrections to the analytic solutions is also proposed. It is therefore shown that the nonlocal optical response of the metal imposes more realistic, finite upper bounds to the enhancement feasible with ultrasmall plasmonic cavities, thus providing a theoretical description closer to state of the art experiments