The propagation of electromagnetic radiation in periodically stratified media is considered. Media of finite, semi-infinite, and infinite extent are treated. A diagonalization of the unit cell translation operator is used to obtain exact solutions for the Bloch waves, the dispersion relations, and the band structure of the medium. Some new phenomena with applications to integrated optics and laser technology are presented.

/pdf/electromagnetic-propagation-in-periodic-stratified-media-i-2kbs7o338q.pdf

Electromagnetic propagation in periodic stratified media. I. General theory

The application of ellipsometry of the study of the adsorption behavior of proteins and synthetic macromolecules at the air-water interface has been investigated. It is shown that for macromolecules the amount adsorbed per unit area, Γ, as determined by ellipsometry, only has a well-defined physical meaning if the refractive-index increment remains constant up to high concentrations present in the adsorbed layer. It has been found experimentally that this conditioned is fulfilled for proteins. The ellipsometric Γ values of some protein agree satisfactorily with those obtained by two independent techniques has been used to investigate the adsorption from solution of κ-casein, bovine serum albumin, and polyvinyl alcohol. For bovine serum albumin, Γ reaches a plateau value of 2.9 mg/m2 for concentrations ≥ 0.05 wt%. The thickness of the adsorbed molecules. For κ-casein, Γ steadily increases with increasing centration and multilayers are formed. The technique provides interesting information on conformational changes in adsorbed macromolecules, on the rate of the process, and on the conditions under which these occur.

Ellipsometry as a tool to study the adsorption behavior of synthetic and biopolymers at the air–water interface

The dispersion relations are solved for waves guided by a thin, lossy metal film surrounded by media of dielectric constant ${\ensuremath{\epsilon}}_{1}$ and ${\ensuremath{\epsilon}}_{3}$. For symmetric structures (${\ensuremath{\epsilon}}_{1}$=${\ensuremath{\epsilon}}_{3}$), there are the usual two Fano modes whose velocity and attenuation vary with film thickness. For very thin films, one of these modes can attain multicentimeter propagation distances when \ensuremath{\lambda}g1 \ensuremath{\mu}m. In addition, there are two leaky waves which correspond to waves localized at the ${\ensuremath{\epsilon}}_{1}$ (or ${\ensuremath{\epsilon}}_{3}$) dielectric-metal interface whose fields decay exponentially across the metal film and radiate an angular spectrum of plane waves into ${\ensuremath{\epsilon}}_{3}$ (or ${\ensuremath{\epsilon}}_{1}$, respectively). Both radiative waves can be interpreted as spatial transients, which could have physical significance near a transverse plane. When ${\ensuremath{\epsilon}}_{1}$\ensuremath{\ne}${\ensuremath{\epsilon}}_{3}$, there are still four distinct solutions for a given film thickness, two radiative and two nonradiative. For lossy films, there are always two nonradiative solutions for thick enough films. As the thickness goes to infinity, the four solutions reduce to two waves, each radiative and nonradiative pair becoming degenerate. The physical interpretation of these solutions and their dependence on dielectric constant and wavelength are discussed.

Surface-polariton-like waves guided by thin, lossy metal films.

A thin artificial magnetic conductor (AMC) structure is designed and breadboarded for radar cross-section (RCS) Reduction applications. The design presented in this paper shows the advantage of geometrical simplicity while simultaneously reducing the overall thickness (for the current design ). The design is very pragmatic and is based on a combination of AMC and perfect electric conductor (PEC) cells in a chessboard like configuration. An array of Sievenpiper's mushrooms constitutes the AMC part, while the PEC part is formed by full metallic patches. Around the operational frequency of the AMC-elements, the reflection of the AMC and PEC have opposite phase, so for any normal incident plane wave the reflections cancel out, thus reducing the RCS. The same applies to specular reflections for off-normal incidence angles. A simple basic model has been implemented in order to verify the behavior of this structure, while Ansoft-HFSS software has been used to provide a more thorough analysis. Both bistatic and monostatic measurements have been performed to validate the approach.

Thin AMC Structure for Radar Cross-Section Reduction

We have measured the subpicosecond optical response of a solid‐state, semiconductor‐to‐metal phase transition excited by femtosecond laser pulses. We have determined the dynamic response of the complex refractive index of VO2 thin films by making pump‐probe optical transmission and reflection measurements at 780 nm. The phase transition was found to be largely prompt with the optical properties of the high‐temperature metallic state being attained within 5 ps. The ultrafast change in complex refractive index enables ultrafast optical switching devices in VO2.

/pdf/femtosecond-laser-excitation-of-the-semiconductor-metal-28oq0b1xsz.pdf

Femtosecond laser excitation of the semiconductor‐metal phase transition in VO2

A model based on sinusoidal steady-state analysis is developed for the position-sensitive detector (PSD), which is approximated as a distributed RC transmission line. This model is used to study the output response of the lateral effect PSD (i) when only one pulse-modulated light beam is incident and (ii) when two light beams of different wavelengths, with one beam modulated at a frequency f and the other beam modulated at a frequency 2f, are incident at the same time. The simulation shows, and experiments confirm, that the transient response of the PSD consists of a position-dependent dead time (time for the output current to sense the change in the induced photocurrent) and a position-independent exponential rise decay time. For the application of resolving the positions of two or more pulsed-modulated light spots, it is shown that there is a position-dependent upper limit on the usable modulation frequency. With the per-unit-length values chosen for the sheet resistance as R=315 Omega /mm and the junction capacitance as C=330 pF/mm, the modulation frequency limit is determined to be 20 kHz. >

Position dependence of the transient response of a position-sensitive detector under periodic pulsed light modulation

Earlier work on lateral-effect position-sensitive detectors (PSD) has used an amplitude detection signal-processing scheme to determine the position of the centroid of the incident light beam on the PSD surface In this work we introduce a phase detection method of position measurement which is based on detecting the phase difference between the sinusoidal currents flowing through the metal electrodes A distributed transmission line model for the PSD and a one-pole model for the transimpedance preamplifier are used in the analysis of the sensor Experimental results are presented and are found to be in close agreement with simulation results It is seen that the spatial resolution is proportional to the modulation frequency With a light modulation frequency of 50 kHz and the introduction of frequency multiplication (/spl times/8) after the transimpedance preamplifier, a spatial resolution of 2 /spl mu/m is demonstrated For application in multi-degree-of-freedom position sensors, we demonstrate the simultaneous detection of centroids of multiple light beams using frequency division multiplexing Application of the phase method of position detection to a two dimensional PSD shows a maximum deviation from linearity of 1% over the working range of the PSD >

Position detection of multiple light beams using phase detection

Modulated ellipsometry for band structure studies of solids and films

Ellipsometry for Modulated Reflection Studies of Surfaces

If the negative-permittivity region in a layered structure is very thin (≲ 300 A for Ag at 6328 A excitation), the two surface plasmons at its interfaces couple in its interior to yield a coupled-surface-plasmon mode whose propagation constant increases with decreasing layer thickness. These modes were observed by measuring reflectance versus angle of incidence through a high-index prism for TM-polarized light. For very thin Ag films, the reflectance minimum diverges from the phase-matching condition, as determined from independently measured refractive indices and thicknesses. This divergence apparently arises from separation of the pole and the zero in the reflectance versus propagation vector as the Ag thickness is decreased.

Coupled surface plasmons in structures with thin metallic layers

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