J. R. Sambles

Scattering matrix method for propagation of radiation in stratified media: attenuated total reflection studies of liquid crystals

We present a new scattering matrix formalism for the modeling of electromagnetic wave propagation in stratified media. It is computationally efficient and stable and is well suited to the layer geometry that is characteristic of stratified materials. It is applied successfully to the modeling of total attenuated reflection in nematic liquid crystals with beyond-critical-angle incidence when the conventional transfer matrix methods normally fail.

Scattering-matrix approach to multilayer diffraction

A new modeling system to determine the optical response function of a multilayer structure with imposed periodicity in the plane of the layers, a multilayer diffraction grating, is described. This new model has two essential ingredients. This model is based on the well-established coordinate transformation procedure developed by Chandezon et al. [ J. Opt. Soc. Am.72, 839– 846 ( 1982)] in which a periodically modulated surface is transformed into a frame in which it is flat, permitting simpler use of Maxwell’s boundary conditions. Then, instead of using the conventional transfer-matrix method, we developed a scattering-matrix technique that permits the modeling of very thick (of the order of 1 μm or greater) multilayer systems with many field components without numerical instability. Model programs have been developed based on this new scattering-matrix approach and tested by comparison with other models and experimental data.

Fabrication and investigation of asymmetric current‐voltage characteristics of a metal/Langmuir–Blodgett monolayer/metal structure

Metal/Langmuir–Blodgett monolayer/metal devices, where the monolayer consists of the dodecyloxyphenylcarbamate of 2‐bromo, 5(2’‐hydroxyethoxy) tetracyanoquinodimethan, a donor‐σ‐acceptor molecular system, have been constructed, and dc current‐voltage (I‐V) characteristics of these devices were recorded at room temperature. For biases of ±20 mV, the I‐V characteristics are linear, changing to a nonlinear form for higher voltages. This nonlinear characteristic exhibited a ln(I)∝V1/4 dependence for both positive and negative voltages up to ±1 V. For positive voltages >+2.0 V for as‐prepared devices and >+1.5 V for annealed devices, a ln(I)∝V3 dependence was observed, revealing a very large increase in current for small voltage changes. Such behavior was not observed for corresponding negative voltages, indicating rectification across a distance approximated by the length of an individual molecule.

Optical characterisation of gold using surface plasmon-polaritons

Measurements are presented of the optical constants of a thin gold film over primarily the visible region of the spectrum using the surface plasmon-polariton resonance condition in the attenuated total-reflection configuration. Using this technique precise results are obtained and these are compared with those found using other experimental methods and also with the classical free-electron model.

Polarisation Conversion through the Excitation of Surface Plasmons on a Metallic Grating

Abstract Surface plasmon-polaritons may be excited by photons at a metal-air boundary if a grating is used to provide the necessary extra momentum. Rotation of the grating so that the grooves are no longer perpendicular to the plane of incidence reduces the coupling efficiency while at the same time producing some s-polarised radiation in the reflected beam. When the grooves are at 45° to the plane of incidence maximum p-s conversion is obtained. Conversion efficiencies of up to 66% have been recorded for silver-coated gratings of appropriate depth. By scanning the angle of incidence and using a crossed polariser on the detector a strong resonance peak is observed. The application of this phenomenon to optical sensing is considered.

Photonic surfaces for surface-plasmon polaritons

We examine the propagation of surface-plasmon polaritons on textured surfaces. Specifically, we look at how a grating surface produces a band gap in the propagation of this mode and how the band gap depends on the propagation direction of the mode. This naturally leads to a discussion of a surface profile suitable for blocking surface mode propagation in all directions. By using a diffractive-optics-based theoretical modeling approach we examine the requirements for such a surface. We then confirm these expectations experimentally by producing a surface exhibiting a band gap for surface-plasmon polariton modes in all directions in the energy range 1.91–2.00 eV.

Determination of the optical permittivity and thickness of absorbing films using long range modes

Analytic theory and numerical modelling are presented for the prism coupling of light to long range surface modes supported by a thin absorbing film. If both transverse magnetic and transverse electric modes can be excited, then by comparing theory to angle dependent reflectivity data the optical permittivity and thickness of the film may be unambiguously established. An experimental confirmation is presented for thin films of indium tin oxide (ITO) on glass substrates. The environment of the ITO is made optically symmetric, to support the long range mode, by use of a fluid which is index matched to the glass substrate. Attenuated total reflection, with prism coupling through the matching fluid, gives, with suitable fluid thickness, sharp resonant modes in the angle dependent reflectivity. Comparison of such data with modelling theory yields the ITO parameters.

Guided modes and surface plasmon-polaritons observed with a nematic liquid crystal using attenuated total reflection

Abstract An aligned layer of nematic liquid crystal with suitable optical anisotropy and under the application of appropriate applied voltages, may support various guided modes of light. Here the attenuated total reflection technique is used to examine such guided modes allowing simultaneous observation of the surface plasmonpolariton (S.P.P.) at a metal/liquid crystal interface. We report observations of the interaction between the bulk guided modes and the S.P.P., an interaction made possible by the strong refractive index anisotropy of the chosen liquid crystal. The influence of applied voltage upon the guided modes, the S.P.P. and their interaction is studied. Detailed reflectivity results are compared with theory for layered uniaxial media.

Slow waves caused by cuts perpendicular to a single subwavelength slit in metal

Resonant transmission of microwaves through a subwavelength slit in a thick metal plate, into which subwavelength cuts have been made, is explored. Two orientations of the cuts, parallel and perpendicular to the long axis of the slit, are examined. The results show that the slits act as though filled with a medium with anisotropic effective relative permeability which at low mode numbers has the two values ~(1, 9.1), increasing to ~(1, 14.4) for higher mode numbers.

Selective transmission through very deep zero-order metallic gratings at microwave frequencies

Zero-order metal grating structures are found to give extraordinary selective transmission at microwave frequencies through the resonant excitation of coupled surface waves. The metal slat structures with dielectric spacings as small as 250 μm strongly transmit wavelengths of several millimeters. A simple interpretation of these novel results which treats the deep grating structures as “filled” Fabry–Perot cavity systems gives model transmissivities which agree very well with the experimental data.