Open Access. Powered by Scholars. Published by Universities.®

Physics Commons™

Open Access. Powered by Scholars. Published by Universities.®

Optics

Discipline
Institution
Publication Year
Publication
Publication Type

Articles 151 - 180 of 180

Full-Text Articles in Physics

Interpretational Difficulties In Quantum Field Theory, P Krekora, Q Su, Rainer Grobe Feb 2006

Interpretational Difficulties In Quantum Field Theory, P Krekora, Q Su, Rainer Grobe

Faculty publications – Physics

Based on space-time-resolved solutions to relativistic quantum field theory we illustrate interpretational difficulties in associating field-theoretical quantities with properties of particles. These difficulties are related to the fact that the definition of the spatial probability density of particles depends on the choice of the Hilbert subspace on which the field operator is projected. We illustrate these problems by analyzing pair-production probabilities and spatial densities for the electron-positron dynamics associated with a spatially localized subcritical potential that is turned on and off in time.

Go to article

Empirical Model For The Electron-Impact K-Shell-Ionization Cross Sections, A K. F Haque, M A. Uddin, A K. Basak, K R. Karim, B C. Saha Jan 2006

Empirical Model For The Electron-Impact K-Shell-Ionization Cross Sections, A K. F Haque, M A. Uddin, A K. Basak, K R. Karim, B C. Saha

Faculty publications – Physics

The total cross sections of electron-impact single-K-shell ionization of 14 atomic targets ranging from H to U (1 <= Z <= 92) are calculated using a modified version of the BELI formula [Bell , J. Phys. Chem. Ref. Data 12, 891 (1983)] by incorporating both ionic and relativistic corrections in it. The proposed modified Bell model with a single set of parameters is found to provide an excellent description of the experimental data in the reduced energy range 1 <= E/I-K <= 10(6) (E and I-K are, respectively, the incident energy and ionization potential) with a performance level at least as good as any of the existing methods and models.

Go to article

Dynamical Control Of Qubit Coherence: Random Versus Deterministic Schemes, Lea F. Santos, Lorenza Viola Dec 2005

Dynamical Control Of Qubit Coherence: Random Versus Deterministic Schemes, Lea F. Santos, Lorenza Viola

Dartmouth Scholarship

We reexamine the problem of switching off unwanted phase evolution and decoherence in a single two-state quantum system in the light of recent results on random dynamical decoupling methods [L. Viola and E. Knill, Phys. Rev. Lett. 94, 060502 (2005)]. A systematic comparison with standard cyclic decoupling is effected for a variety of dynamical regimes, including the case of both semiclassical and fully quantum decoherence models. In particular, exact analytical expressions are derived for randomized control of decoherence from a bosonic environment. We investigate quantitatively control protocols based on purely deterministic, purely random, as well as hybrid design, and …

Go to article

Klein Paradox With Spin-Resolved Electrons And Positrons, P Krekora, Q Su, Rainer Grobe Dec 2005

Klein Paradox With Spin-Resolved Electrons And Positrons, P Krekora, Q Su, Rainer Grobe

Faculty publications – Physics

Using numerical solutions to relativistic quantum field theory with space-time resolution, we illustrate how an incoming electron wave packet with a definite spin scatters off a supercritical potential step. We show that the production rate is reduced of only those electrons that have the same spin as the incoming electron is reduced. This spin-resolved result further clarifies the importance of the Pauli-exclusion principle for the Klein paradox.

Go to article

Electron-Impact Ionization Of Hydrogen And Lithiumlike Systems, M A. Uddin, Abul Kalam Fazlul Haque, A K. Basak, Khondkar R. Karim, B C. Saha Sep 2005

Electron-Impact Ionization Of Hydrogen And Lithiumlike Systems, M A. Uddin, Abul Kalam Fazlul Haque, A K. Basak, Khondkar R. Karim, B C. Saha

Faculty publications – Physics

The electron impact single ionization cross sections on a number of targets with atomic number Z=1-92 in the H and Li isoelectronic sequences are calculated using a modified version of the recently propounded relativisitic improved binary-encounter dipole (MRIBED) model [M. A. Uddin , Phys. Rev. A 70, 032706 (2004); 71, 032715 (2005)]. The modified RQIBED (MRIBED) model along with a Z-dependent factor in it is found remarkably successful in the applications to H- and Li-like systems and also valid for the ionization of a filled s orbit including the He-like targets.

Go to article

Computation Of Electron-Impact K-Shell Ionization Cross Sections Of Atoms, M A. Uddin, Abul Kalam Fazlul Haque, M Masum Billah, A K. Basak, Khondkar R. Karim, B C. Saha Mar 2005

Computation Of Electron-Impact K-Shell Ionization Cross Sections Of Atoms, M A. Uddin, Abul Kalam Fazlul Haque, M Masum Billah, A K. Basak, Khondkar R. Karim, B C. Saha

Faculty publications – Physics

The total cross sections of electron impact single K-shell ionization of atomic targets, with a wide range of atomic numbers from Z=6-50, are evaluated in the energy range up to about 10 MeV employing the recently proposed modified version of the improved binary-encounter dipole (RQIBED) model [Uddin , Phys. Rev. A 70, 032706 (2004)], which incorporates the ionic and relativistic effects. The experimental cross sections for all targets are reproduced satisfactorily even in the relativistic energies using fixed generic values of the two parameters in the RQIBED model. The relativistic effect is found to be significant in all targets except …

Go to article

Thorium-Based Thin Films As Highly Reflective Mirrors In The Euv, David D. Allred, William R. Evans, Jed E. Johnson, Richard L. Sandberg, R. Steven Turley Jan 2005

Thorium-Based Thin Films As Highly Reflective Mirrors In The Euv, David D. Allred, William R. Evans, Jed E. Johnson, Richard L. Sandberg, R. Steven Turley

Faculty Publications

As applications for extreme ultraviolet (EUV) radiation have been identified, the demand for better optics has also increased. Thorium and thorium oxide thin films (19 to 61 nm thick) were RF-sputtered and characterized using atomic force microscopy (AFM), spectroscopic ellipsometry, low-angle x-ray diffraction (LAXRD), x-ray photoelectron spectroscopy (XPS), and x-ray absorption near edge structure (XANES) in order to assess their capability as EUV reflectors. Their reflectance and absorption at different energies were also measured and analyzed at the Advanced Light Source in Berkeley. The reflectance of oxidized thorium is reported between 2 and 32 nm at 5, 10, and 15 …

Go to article

Optical Wave Propagation In Discrete Waveguide Arrays, Jared Hudock Jan 2005

Optical Wave Propagation In Discrete Waveguide Arrays, Jared Hudock

Electronic Theses and Dissertations

The propagation dynamics of light in optical waveguide arrays is characteristic of that encountered in discrete systems. As a result, it is possible to engineer the diffraction properties of such structures, which leads to the ability to control the flow of light in ways that are impossible in continuous media. In this work, a detailed theoretical investigation of both linear and nonlinear optical wave propagation in one- and two-dimensional waveguide lattices is presented. The ability to completely overcome the effects of discrete diffraction through the mutual trapping of two orthogonally polarized coherent beams interacting in Kerr nonlinear arrays of birefringent …

Go to article

Transitions Into The Negative-Energy Dirac Continuum, P Krekora, Q Su, Rainer Grobe Nov 2004

Transitions Into The Negative-Energy Dirac Continuum, P Krekora, Q Su, Rainer Grobe

Faculty publications – Physics

We compare the predictions of the single-particle Dirac equation with quantum field theory for an electron subjected to a space and time dependent field. We demonstrate analytically and numerically that a transition into the negative-energy subspace predicted by the single-particle Dirac equation is directly associated with the degree of suppression of pair-production as described by quantum field theory. We show that the portion of the mathematical wave function that populates the negative-energy states corresponds to the difference between the positron spatial density for systems with and without an electron initially present.

Go to article

Chemical Structure - Nonlinear Optical Property Relationships For A Series Of Two-Photon Absorbing Fluorene Molecules, Joel Mccajah Hales Jan 2004

Chemical Structure - Nonlinear Optical Property Relationships For A Series Of Two-Photon Absorbing Fluorene Molecules, Joel Mccajah Hales

Electronic Theses and Dissertations

This dissertation reports on the investigation of two-photon absorption (2PA) in a series of fluorenyl molecules. Several current and emerging technologies exploit this optical nonlinearity including two-photon fluorescence imaging, three-dimensional microfabrication, site-specific photodynamic cancer therapy and biological caging studies. The two key features of this nonlinearity which make it an ideal candidate for the above applications are its quadratic dependence on the incident irradiance and the improved penetration into absorbing media that it affords. As a consequence of the burgeoning field which exploits 2PA, it is a goal to find materials that exhibit strong two-photon absorbing capabilities. Organic materials are …

Go to article

A Test Of Bell’S Inequality For The Undergraduate Laboratory, Burton A. Betchart Jan 2004

A Test Of Bell’S Inequality For The Undergraduate Laboratory, Burton A. Betchart

Honors Papers

The thesis documents the work done over the year to initiate an undergraduate Advanced Laboratory experiment which tests Bell’s inequality. It provides reference theory for the experiment, including explanations of Bell inequalities, basics of nonlinear optics, type-I downconversion and entanglement, and polarization states of the entangled photons. A main result is the equipment and design proposal for the experiment, which will cost a total $19600, led in price by the $9000 of a four photodetector array and followed by the $5000 of a 405nm pump laser. Entangled photons are produced by pumping BBO in a two-crystal geometry. Although most of …

Go to article

Evaluation Of The Photo-Induced Structural Mechanisms In Chalcogenide, Cedric Lopez Jan 2004

Evaluation Of The Photo-Induced Structural Mechanisms In Chalcogenide, Cedric Lopez

Electronic Theses and Dissertations

Chalcogenide glasses and their use in a wide range of optical, electronic and memory applications, has created a need for a more thorough understanding of material property variation as a function of composition and in geometries representative of actual devices. This study evaluates compositional dependencies and photo-induced structural mechanisms in As-S-Se chalcogenide glasses. An effective fabrication method for the reproducible processing of bulk chalcogenide materials has been demonstrated and an array of tools developed, for the systematic characterization of the resulting material's physical and optical properties. The influence of compositional variation on the physical properties of 13 glasses within the …

Go to article

Polarimetric Characterization Of Random Electromagnetic Beams And Applications, Mircea Mujat Jan 2004

Polarimetric Characterization Of Random Electromagnetic Beams And Applications, Mircea Mujat

Electronic Theses and Dissertations

Polarimetry is one of the principal means of investigating the interaction of light with matter. Theoretical models and experimental techniques are presented in this dissertation for polarimetric characterization of random electromagnetic beams and of signatures of random media in different scattering regimes and configurations. The degree of polarization rather than the full description of the state of polarization is of interest in multiple scattering and free space propagation where the statistical nature and not the deterministic component of light bears the relevant information. A new interferometric technique for determining the degree of polarization by measuring the intensity fluctuations in a …

Go to article

Stable Spatial Solitons In Semiconductor Optical Amplifiers, Erdem Ultanir Jan 2004

Stable Spatial Solitons In Semiconductor Optical Amplifiers, Erdem Ultanir

Electronic Theses and Dissertations

A spatial soliton is a shape invariant self guided beam of light or a self induced waveguide. Spatial solitons appear as a result of the balance of diffraction and nonlinear focusing in a system. They have been observed in many different conservative media in the last couple of years. Solitons are ubiquitous, because of the probability of using their interactions in optical data processing, communications etc. Up to now due to the power required to generate the solitons, and the response times of the soliton supporting media, these special waves of nature could not penetrate the applications arena. Semiconductors, with …

Go to article

Dispersion-Managed Breathing-Mode Semiconductor Mode-Locked Ring Laser, Bojan Resan Jan 2004

Dispersion-Managed Breathing-Mode Semiconductor Mode-Locked Ring Laser, Bojan Resan

Electronic Theses and Dissertations

A novel dispersion-managed breathing-mode semiconductor mode-locked ring laser is developed. The "breathing-mode" designation derives from the fact that intracavity pulses are alternately stretched and compressed as they circulate around the ring resonator. The pulses are stretched before entering the semiconductor gain medium to minimize the detrimental strong integrating self-phase modulation and to enable efficient pulse amplification. Subsequently compressed pulses facilitate bleaching the semiconductor saturable absorber. The intracavity pulse compression ratio is higher than 50. Down chirping when compared to up chirping allows broader mode-locked spectra and shorter pulse generation owing to temporal and spectral semiconductor gain dynamics. Pulses as short …

Go to article

Dephasing Model For Spatially Extended Atomic States In Cyclotronlike Resonances, R E. Wagner, S Radovich, J Gillespie, Q Su, Rainer Grobe Oct 2002

Dephasing Model For Spatially Extended Atomic States In Cyclotronlike Resonances, R E. Wagner, S Radovich, J Gillespie, Q Su, Rainer Grobe

Faculty publications – Physics

In recent work, the formation of ring-shaped electron distributions for hydrogen atoms in resonant static magnetic-laser fields has exclusively been associated with the impact of relativity. In this note we will generalize this statement and show that the nonlinearity associated with the nuclear binding force can trigger similarly shaped steady-state charge clouds in atoms under suitable conditions. The dephasing model, based on modeling the quantum-mechanical state by a classical ensemble of quasiparticles evolving with slightly different cyclotron periods, can recover features, in the two lowest-order resonances as well as the Coulomb-field-induced charge distributions.

Go to article

Electric-Field-Induced Relativistic Larmor-Frequency Reduction, P Krekora, Q Su, Rainer Grobe Jul 2002

Electric-Field-Induced Relativistic Larmor-Frequency Reduction, P Krekora, Q Su, Rainer Grobe

Faculty publications – Physics

Using the numerical solution to the time-dependent Dirac equation we show that the effect of relativity on the usual Larmor period for an electron in a magnetic field can be enhanced drastically if a suitably scaled and aligned static electric field is added to the interaction. This electric field does not change the electron's speed but leads to an elliptical spin precession due to relativity. This spin precession is accompanied by a position-dependent spin distribution.

Go to article

Critique Of The Wigner Tunneling Speed And A Proposed Alternative, P Krekora, Q Su, Rainer Grobe Aug 2001

Critique Of The Wigner Tunneling Speed And A Proposed Alternative, P Krekora, Q Su, Rainer Grobe

Faculty publications – Physics

In the context of superluminal propagation of wave packets through potential barriers, the tunneling speed is usually characterized by the Wigner velocity. We propose an alternative speed that takes into account the interference between the incoming and the reflected waves and leads to a better estimation of arrival time for a wave packet entering the tunneling region. This arrival time is derived by an extrapolation from inside the barrier. The analytical theory is based on the stationary phase approximation whose validity is justified by a comparison with the numerical solution of the time-dependent Dirac equation.

Go to article

The Vacuum Excitation And Squeezing Properties Of Two Quantum Oscillators With Delta-Kicked Interactions, J Y. Ji, David Peak Apr 2001

The Vacuum Excitation And Squeezing Properties Of Two Quantum Oscillators With Delta-Kicked Interactions, J Y. Ji, David Peak

All Physics Faculty Publications

The vacuum excitation and squeezing of two harmonic oscillators with delta-kicked interactions for four types of elementary coupling are studied. The exact quantum motion for the Heisenberg operators and the explicit form of squeezing operators are found. The variances are calculated to study the squeezing properties for position, momentum and generalized quadrature operators.

Go to article

Effects Of Relativity On The Time-Resolved Tunneling Of Electron Wave Packets, P Krekora, Q Su, Rainer Grobe Mar 2001

Effects Of Relativity On The Time-Resolved Tunneling Of Electron Wave Packets, P Krekora, Q Su, Rainer Grobe

Faculty publications – Physics

We solve numerically the time-dependent Dirac equation for a quantum wave packet tunneling through a potential barrier. We analyze the spatial probability distribution of the transmitted wave packet in the context of the possibility of effectively superluminal peak and front velocities of the electron during tunneling. Both the Dirac and Schrodinger theories predict superluminal tunneling speeds. However, in contrast to the Dirac theory the Schrodinger equation allows a possible violation of causality. Based on an analysis of the tunneling process in full temporal and spatial resolution, we introduce an instantaneous tunneling speed that can be computed inside the potential barrier.

Go to article

Numerical Study Of Optical Delay In Semiconductor Multilayer Distributed Bragg Reflector And Tunable Microcavity Structures, Michael I. K. Etan Mar 2001

Numerical Study Of Optical Delay In Semiconductor Multilayer Distributed Bragg Reflector And Tunable Microcavity Structures, Michael I. K. Etan

Theses and Dissertations

The Air Force has a growing need for the greater bandwidth, speed, and flexibility offered by optical communication links. Future space systems and airborne platforms will most likely use optical signals for efficient power transmission and to minimize the possibility of spoofing and eavesdropping. Tunable optical delays play an important role in the implementation of free space optical communication links. The primary challenge in implementing these systems is the active maintenance of coherent wave fronts across the system's optical aperture. For space applications, this aperture may he hundreds of meters in diameter. Spatial segmentation of a large aperture into smaller …

Go to article

Dirac Theory Of Ring-Shaped Electron Distributions In Atoms, P Krekora, R E. Wagner, Q Su, Rainer Grobe Feb 2001

Dirac Theory Of Ring-Shaped Electron Distributions In Atoms, P Krekora, R E. Wagner, Q Su, Rainer Grobe

Faculty publications – Physics

The time-dependent Dirac equation is solved numerically on a space-time grid for an atom in a strong static magnetic field and a laser field. The resonantly induced relativistic motion of the atomic electron leads to a ringlike spatial probability density similar to the features that have been recently predicted [Wagner, Su, and Grobe, Phys. Rev. Lett. 84, 3282 (2000)] based on a phase-space method. We further demonstrate that spin-orbit coupling for a fast-moving electron in such an atom becomes significant and the time dependence of the spin can dephase even if initially aligned parallel to the direction of the static …

Go to article

Classical Versus Quantum Dynamics For A Driven Relativistic Oscillator, Rainer Grobe, Qichang Su, P J. Peverly, R E. Wagner Mar 2000

Classical Versus Quantum Dynamics For A Driven Relativistic Oscillator, Rainer Grobe, Qichang Su, P J. Peverly, R E. Wagner

Faculty publications – Physics

We compare the time evolution of the quantum-mechanical spatial probability density obtained by solving the time-dependent Dirac equation with its classical counterpart obtained from the relativistic Liouville equation for the phase-space density in a regime in which the dynamics is essentially relativistic. For a resonantly driven one-dimensional harmonic oscillator, the simplest nontrivial model system to perform this comparison, we find that, despite the nonlinearity induced by relativity, the classical ensemble description matches the quantum evolution remarkably well.

Go to article

Basic Astronomy Labs, Terry L. Smith, Michael D. Reynolds, Jay S. Huebner Jan 1996

Basic Astronomy Labs, Terry L. Smith, Michael D. Reynolds, Jay S. Huebner

Physics Faculty Research and Scholarship

Providing the tools and know-how to apply the principles of astronomy first-hand, these 43 laboratory exercises each contain an introduction that clearly shows budding astronomers why the particular topic of that lab is of interest and relevant to astronomy. About one-third of the exercises are devoted solely to observation, and no mathematics is required beyond simple high school algebra and trigonometry.Organizes exercises into six major topics—sky, optics and spectroscopy, celestial mechanics, solar system, stellar properties, and exploration and other topics—providing clear outlines of what is involved in the exercise, its purpose, and what procedures and apparatus are to be used. …

Go to article

Interview: Brenda Laurel, Jason Challas Jul 1995

Interview: Brenda Laurel, Jason Challas

SWITCH

This interview with Brenda Laurel, Virtual Reality (VR) author and thinker, discusses the applications and challenges of VR. Creating an emphatic experience using VR technology is possible, but the challenge lies in designing an environment that models the senses to stimulate emotions. VR enables experiences of different genders, but physiological differences between the sexes exist and are important to understand. However, technology used to create the environment and simulation of physical objects in VR is only in the developmental stage. Laurel believes in the importance of keeping the mind grounded in the physical body, in order to strengthen the appreciation …

Go to article

Optical Properties Of Human Uterus At 630 Nm, Steen J. Madsen, Bruce J. Tromberg, Yona Tadir, Pius Wyss, Lars O. Svaasand, Richard C. Haskell Jan 1994

Optical Properties Of Human Uterus At 630 Nm, Steen J. Madsen, Bruce J. Tromberg, Yona Tadir, Pius Wyss, Lars O. Svaasand, Richard C. Haskell

All HMC Faculty Publications and Research

The optical properties of normal and fibriotic human uteri were determined using frequency-domain and steady-state techniques .

Go to article

Actino- And Thermo- Response Of Molybdenite In Vacuo With Various Colored Lights, John H. Fulton Jul 1931

Actino- And Thermo- Response Of Molybdenite In Vacuo With Various Colored Lights, John H. Fulton

Master's Theses or Doctor of Nursing Practice

The purposes of this investigation are to study the reaction of molybdenite cells to light of various colors while in vacuo and at various temperatures. The samples of molybdenite were also subjected to radiant heat in the last part of the experiment, which was undertaken to determine to some extent the amount of thermos-electric effect which was due to thermal radiation in the first part of the investigation.

Go to article

An Investigation Of The Thermo- And Actino- Electric Properties Of Molybdenite, William Otis Johnson May 1931

An Investigation Of The Thermo- And Actino- Electric Properties Of Molybdenite, William Otis Johnson

Master's Theses or Doctor of Nursing Practice

Considerable work has been done on various mineral substances and chemical compounds within recent years to ascertain, if possible, whether the substance possessed any degree of photo- or thermos-sensitivity; and, to determine the characteristics of these responses. Among the most prominent substances which have been tested are selenium, bismuth, antimony, hematite, stibnite, and molybdenite. It was the purpose of this investigation to summarize the phenomena that have occurred within samples of molybdenite under a variety of conditions involving heat, light, and e.m.f.

Go to article

The Three-Point Gap As A Means Of Control In Instantaneous Photography, Elgin Albert Denio Jan 1931

The Three-Point Gap As A Means Of Control In Instantaneous Photography, Elgin Albert Denio

Master's Theses or Doctor of Nursing Practice

In 1926, Wynn Williams investigated the theory of the three-point gap, which phenomenon had been known and utilized for some time but until his investigation was not understood theoretically. This investigation has been divided into two distinct parts: First, when the energy was generated by a large Toepler-Holtz station machine; and second when the energy was generated by a one-kilowatt, 25,000 volt transformer.

Go to article

A Study Of The Striated Spark By The Method Of Instantaneous Photography, Laurence L. Cruise May 1930

A Study Of The Striated Spark By The Method Of Instantaneous Photography, Laurence L. Cruise

Master's Theses or Doctor of Nursing Practice

In 1867 Toepler found the existence of a pulse spreading from the region around the spark immediately after it had passed. Since the density of the air in the pulse differs from that of the surrounding gas, the pulse is optically different from the rest of the field and so can be made visible by the “Shadowgraph Method.” Topeler’s work was the first of its kind where an instantaneous view, say of the order of several millionths of a second, of the electric spark was obtained. IN 1926 Dr. Zinszer, while studying the life history of the electric spark by …

Go to article

First Prev