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.

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Electromagnetic propagation in periodic stratified media. I. General theory

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.

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

An antenna system and an artificial magnetic conductor (300) include a
frequency selective surface having a frequency dependent permeability µ 1 z in a
direction normal to the frequency dependent surface, a conductive ground plane
(806), and a rodded media (808) disposed between the frequency selective surface
and the conductive ground plane.

Multi-resonant, high-impedance surfaces containing loaded-loop frequency selective surfaces

Vanadium dioxide single-crystal precipitates with controlled particle sizes were produced in an amorphous, fused SiO2 host by the stoichiometric coimplantation of vanadium and oxygen ions and subsequent thermal processing. The effects of the vanadium dioxide nanocrystal size, nanocrystal morphology, and particle/host interactions on the VO2 semiconductor-to-metal phase transition were characterized. VO2 nanoparticles embedded in amorphous SiO2 exhibit a sharp phase transition with a hysteresis that is up to 50 °C in width—one of the largest values ever reported for this transition. The relative decrease in the optical transmission in the near-infrared region in going from the semiconducting to the metallic phase of VO2 ranges from 20% to 35%. Both the hysteresis width and the transition temperature are correlated with the size of the precipitates. Doping the embedded VO2 particles with ions such as titanium alters the characteristics of the phase transition, pointing the way to control the hysteresis beha...

Synthesis and characterization of size-controlled vanadium dioxide nanocrystals in a fused silica matrix

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 >

A. B. Buckman

Papers

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

Position detection of multiple light beams using phase detection

Electroreflectance Changes in Dielectric Constants of Au and Ag by Modulated Ellipsometry

Modulated ellipsometry for band structure studies of solids and films

Ellipsometry for Modulated Reflection Studies of Surfaces