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Physics Conference Room, SB B326
Coffee starts at 12:00 PM and talk starts at 12:15 PM
Humeyra Caglayan - Wednesday, February 6, 2013
ABSTRACT: Bringing circuit functionalities into the optical domain requires the introduction of new conceptual paradigms and experimental methods, and would represent an important advance in nanoelectronics technology. In this seminar, I will introduce the lumped circuit elements in the near infrared regime by making use of plasmonic materials and simple geometries with subwavelength cross-sectional dimensions. The control of the functionality of these optical nanocircuits, completely consistent and analogous with the notion of radio-frequency circuits, and can be done by changing the impedances of the circuit elements. Such nanocircuits' elements function as building blocks for future plasmonic devices.
I will also present a novel structure that effectively behaves as an n=0 metastructure in the visible and near-infrared spectral range. This metal/dielectric optical waveguide structure operating at the cutoff of its TE mode behaving effectively as an Epsilon-Near-Zero (ENZ) metamaterial, exhibiting uniform phase distribution and essentially uniform amplitude, which enables opportunities for better control and enhancement of light propagation in waveguides, as well as development of nano-photonic devices. Finally, I will discuss the effect of the ENZ medium on the control of degree of coherence by comparing the field radiated by sources with varying degrees of randomness in a conventional medium to that in an ENZ medium.
Alexander Khanikaev - Monday, February 11, 2013
ABSTRACT: Metamaterials, the artificial electromagnetic media with properties beyond those found in natural materials, have been a subject of intensive studies for over a decade and as the field evolves, new avenues for their applications are emerging. In this talk, I will focus on the possible applications of Fano resonant metamaterials stemming from their ability of enhancing light-matter interaction due to strong confinement of electromagnetic field by subradiant modes. I will show how metamaterials can be endowed with new unique functionalities by combining them with other complex media, such as magnetic materials, biomolecules, and graphene. In particular, the nonreciprocity can be engineered and ultra-thin optical diodes can be created by combining metamaterials with magneto-optical materials. It will also be shown how the interaction of high-quality mid-IR modes of Fano-resonant metamaterials with the vibrational modes of biomolecules facilitates the detection of protein monolayers and their characterization to an unprecedented degree. Finally, I will present our recent theoretical and experimental results on light scattering in metamaterial/graphene heterostructures and propose how such hybrid photonic-electronic systems can be used to build tunable photonic devices.
Pai-Yen Chen - Wednesday, February 13, 2013
ABSTRACT: Plasmonics has opened the possibility to strongly enhance light-matter interaction at the nanoscale, opening new opportunities to manipulate and confine light at dimensions unthinkable only a few years ago. Plasmonic nanostructures can enhance weak optical responses and nonlinear optical effects, and can serve as information carriers for the next-generation of heavily integrated nanophotonic systems. Optical metamaterials formed by large arrays of subwavelength plasmonic nanostructures can open even more exciting scenarios, by exploiting the collective coupling interaction among many nanoinclusions to realize bulk optical properties that cannot be found in nature, such as a negative optical index of refraction. In my talk,I will describe our recent research efforts on optical nanoantenna arrays and optical metamaterials, studying their exciting physics and their practical use and application in highly-efficient thermoelectric and thermophotovoltaic solar cells, photothermal therapy and nanoscale nonlinear optical processes, including wave mixing, harmonic generation, phase conjugation and optical bistable effects. In addition, I will discuss how the extreme local field enhancement around nanoantennas can benefit ultrafast photon-assisted field emission processes, optical heterodyne terahertz (THz) generation and multiple-photon photoemission from nano-emitters, enabling compact, low-cost, low-power THz generation, free-electron lasers and X-ray sources. I will also discuss how the anti-phase polarization of a plasmonic coating may be used to realize invisibility and transparency effects. As an extreme case of light manipulation at the "atomic" scale, I will discuss the collective oscillation of massless Dirac fermions inside grapheme monolayers, in which surface plasmon polaritons may be controlled by the graphene's tunable surface conductivity using electrostatic gating. I will conclude my talk discussing active and tunable THz nanodevices and nanocircuits, and graphene-based THz metamaterials.
Boris Shapiro - Wednesday, February 20, 2013
ABSTRACT: A hot body radiates an electromagnetic flux according to Kirchhoff's law. However, close to the body surface there are strong fluctuating fields which do not contribute to the electromagnetic flux. These fields are evanescent and decay exponentially away from the surface. Some phenomena, related to those fields, will be discussed and the effect of stationary currents on the electromagnetic field fluctuations will be pointed out.
Hanwei Gao - Monday, March 4, 2013
ABSTRACT: Surface plasmons have been investigated intensively because of their unique properties for optical confinement and light manipulation on subwavelength scales. Research on both fundamentals and applications of surface plasmons are advanced by rapid development of nanoscale synthesis and fabrication techniques. By defining nanostructures in metals, these traditional electrical conductors are functionalized with plasmonic properties, which have led to exotic phenomena such as negative light refraction, surface enhanced Raman scattering, and subwavelength focusing. In this talk, I will discuss how surface plasmons in periodically patterned metals can be identified, characterized, and tuned using near-field and far-field optical methods. These periodic nanostructures, also known as plasmonic crystals, provide versatile platforms for discovering and screening new plasmonic materials. Rationally designed plasmonic crystals have also shown promises for applications from biochemical sensing to solar energy harvesting.
Alessandro Salandrino - Wednesday, March 6, 2013
ABSTRACT: Diffraction effects are ubiquitous in all phenomena involving the propagation of waves. As an example, in optics and photonics the so-called "diffraction limit" imposes a fundamental limit on the resolution that an optical instrument can achieve, or on the confinement that a beam can maintain during propagation. In this talk I will present novel strategies to manage or to completely counteract the effects of diffraction. The far reaching consequences of the proposed schemes include the possibility of achieving far-field sub-diffraction imaging, evanescent wave recovery and diffraction-free, self-healing plasmonic propagation.
Hebin Li - Monday, March 11, 2013
ABSTRACT: The concept of multi-dimensional Fourier transform spectroscopy originated in nuclear magnetic resonance (NMR) where it revolutionized NMR studies of molecular structure and dynamics and led to the Nobel Prize in Chemistry in 1991. In the past decade, the same concept has been implemented in the optical region with femtosecond lasers. In the experiment, the nonlinear response of a sample to multiple laser pulses is measured as a function of time delays. A multi-dimensional spectrum is constructed by taking a multi-dimensional Fourier transform of the signal with respect to multiple time delays.
In this presentation, I will introduce optical multi-dimensional Fourier transform spectroscopy and its applications to study a potassium (K) vapor and semiconductor nanostructures. The K vapor provides a simple test model to validate the method, while the obtained 2D spectra reveal the surprising collective resonance due to the dipole-dipole interaction in a dilute gas. By extending the technique into a third dimension, 3D spectra can unravel different pathways in a quantum process and provide complete and unambiguous information to construct the full Hamiltonian of the system. Besides atomic/molecular systems, optical multi-dimensional Fourier-transform spectroscopy is also a powerful tool for studying many-body dynamics and coupling in solid-state systems such as semiconductor nanostructures. I will present several applications in semiconductor quantum wells and self-assembled quantum dots, where unique information about the systems can be obtained from 2D spectra.
Ryan Thomas Glasser - Monday, March 18, 2013
ABSTRACT: Quantum states of light have been shown to provide improvements in a variety of systems, resulting in provably secure communication, sub-shot noise interferometry, and computation schemes that scale better with resources than when using classical means. A key aspect of these entangled and squeezed states of light is that they exhibit correlations that are stronger than allowed classically. Due to the important role entanglement plays in the field of quantum optics, numerous investigations into its fundamental behavior have taken place. For example, how entanglement evolves when propagating through a slow light medium, in which the group velocity of light is less than the speed of light in vacuum, c, have been conducted in the past. We seek to investigate how quantum correlations and entanglement behave when propagating through a medium exhibiting anomalous dispersion. In such a medium, optical pulses may propagate with group velocities that are larger than c, or even negative. In this talk I will show that by using a nondegenerate four-wave mixing (4WM) process in warm rubidium vapor, which may be used to generate squeezed and entangled states of light, it is possible to generate pulses with record negative group velocities. Additionally, I will discuss recent results involving the combination of fast light and quantum entanglement. Finally, I will present ongoing research involving secure quantum key distribution and phase-sensitive image amplification, and conclude with a discussion of future research directions involving the versatile 4WM system.
Ravindra Bhatt - Monday, April 8, 2013
David Grier - Monday, April 29, 2013
ABSTRACT: This talk focuses on the statistical mechanics of micrometer colloidal particles moving through landscapes of force and torque that are created with computer-generated holograms. These optical force fields can take the form of discrete optical tweezers that can trap and hold microscopic objects in three dimensions. They also can be far more exotic, and include the first experimental implementation of a knotted force field, and the first successful demonstration of a true tractor beam. In addition to the conservative forces that create traps, holographically structured light fields also exert non-conservative forces whose intriguing ramifications we observe with holographic video microscopy. These observations reveal a previously unrecognized category of stochastic heat engines.
Zhou Shi - Monday, September 16, 2013
Eric Cramer - Monday, September 23, 2013
ABSTRACT: Although lightning is one of the most commonly known and destructive natural phenomena on Earth, it remains poorly understood in terms of the most basic physics. Questions such as how it is created inside thunderstorms and how it manages to travel many tens of kilometers are still being worked out today. Benjamin Franklin is considered to be the pioneer of this research field, propelled by his famous kite experiment that showed lightning to be an electrical discharge. Since that time, lightning experiments have been relatively difficult to achieve due to its seemingly random occurrence, unpredictability and short duration. However, over the last decade, the research groups at Florida Institute of Technology and the University of Florida have made detailed measurements of the lightning discharge using a rocket triggering technique at the International Center for Lightning Research and Testing (ICLRT). A consequence of this study has been the discovery that lightning emits x-rays and gamma-rays as it travels through the atmosphere and down to Earth's surface. In 1994, NASA satellite data from the Compton Gamma-Ray Observatory, originally designed to measure gamma-ray bursts from distant galaxies, discovered intense glows of radiation being emitted from the Earth. These discharges were so bright (up to 40 MeV), that they saturated all the high energy detectors onboard the spacecraft. After many similar events were observed, these phenomena, known as Terrestrial Gamma-Ray Flashes (TGFs), were shown to originate from within the thunderstorm region. Most recently, the potential radiation doses that airline passengers would experience inside the core of a TGF have been calculated. It has also been determined, with remote radio measurements and theoretical modeling, that a new type of electrical discharge, called "dark lightning", is responsible for these high energy events. However, its relationship to a normal lightning discharge still remains a mystery. Many other exotic phenomena have also been observed as a result of thunderstorms including halos, elves, sprites and blue jets. The fact that these lightning related events can affect the upper atmosphere and lower ionosphere has reshaped the scientific field to the study of high energy atmospheric physics. The research done on lightning has thus fused many areas of physics including plasma physics, atmospheric physics, and quantum electrodynamics. The rapidly expanding field has opened many opportunities for both theoretical and experimental studies. Mathematical modeling, including Monte Carlo simulations, has given us a better understanding about the nature of particle acceleration inside the high field regions of thunderstorms. Likewise, instrumentation including photomultiplier tubes, high speed video cameras, and electric field antennas, has helped us gain a better insight into the lightning discharge near the ground. In this talk, we review the history of lightning research, show many of its recent developments, and lay out the questions that are being addressed today by many physicists, meteorologists and engineers around the world. We also hope to expand the importance of lightning safety and the awareness of exciting research opportunities for many young scientists.
Neepa Maitra - Monday, September 30, 2013
Seppe Kuehn - Tuesday, October 15, 2013
Emil Prodan - Monday, October 21, 2013
ABSTRACT: Topological Insulators and Superconductors are novel materials with non-trivial energy-band topology. This non-triviallity has important physical consequences, such as the emergence of chiral edge or surface bands at the boundary of the samples, or quantized electric and magneto-electric responses. Depending on their generic symmetries, the topological materials fall in several distinct classes. An ongoing effort is understanding what are the physical properties that remain robust in the presence of strong disorder. Some fundamental questions, which apply to all these distinct classes of topological materials, are: Do the edge and surface modes localize? Are there extended states in the bulk (as in the IQHE)? Does the Magneto-Electric response remain quantized in the presence of strong disorder? In this talk, I will give a brief historical account of the field and bring up-front some of the present challenges and new research directions. In the second part I will introduce a non-commutative geometry program for topological insulators, which enabled us to make analytical and computational progress in the field of strongly disordered topological materials.
Dmitri Vainchtein - Monday, October 28, 2013
ABSTRACT: In my talk I discuss several aspects of transport phenomena in the near-integrable multiscale dynamical system. Multi-scale systems naturally arise when a small perturbation is added to an integrable base (or unperturbed) subsystem. Not only are such systems common in various applications, this is the only class of dynamical systems that generically affords a quantitative analytical treatment. Direct brute-force numerical simulation of such systems are possible, but usually are very challenging precisely due to a big separation of time scales. Approximate analytical tools represent an important alternative for studying such systems. An approach that greatly simplifies the description of the mixing dynamics in multi-scale systems is based on the method of averaging: in order to study long-time dynamics, the equations of motion for phase points are averaged over the fast time scale(s). In the present talk I illustrate the glory and the fall of the method of averaging by considering two examples: one from microfluidics and one from plasma physics. In the first part of the talk I consider mixing via resonances-induced chaotic advection in microdroplets. I show that proper characterization of the mixing quality requires introduction of two different metrics. The first metric determines the relative volumes of the domain of chaotic streamlines and the domain of regular streamlines. The second metric describes the time for homogenization inside the chaotic domain. In the second part of my talk, I describe the resonant interaction between monochromatic electromagnetic waves and magnetized electrons in configurations with magnetic field reversals (e.g. in the earth magnetotail). I discuss in two resonant phenomena occurring during slow passages of a particle through a resonance: capture into resonance and scattering on resonance. These processes result in destruction of adiabatic invariant, chaotization and almost free acceleration of particles. We calculate the characteristic times of mixing due to resonant effects and the rates of the acceleration.
Barry P. Rand - Monday, November 11, 2013
ABSTRACT: In this seminar, we will focus on two aspects of our work that look at materials which have been studied for quite some time, but try to utilize them in new and interesting ways. In the first part, we will look at metals, specifically Au and Ag. It turns out that metals, like semiconductors, can be quantized for diameters <2 nm. At such sizes in fact, even relatively efficient quantum yields of emission have been demonstrated. Here, we look at thin films of metal nanoclusters (MNCs), and demonstrate a thin film LED with either Au or Ag MNCs as the emitting element. In both cases, the electroluminescence peak of the LED corresponds with the photoluminescence of the MNCs in solution. In the second part, we will focus on our recent efforts to template the growth of organic semiconductors. Through proper control of crystal phase, molecular orientation, and grain size (from nm to μm), we are able to realize higher solar cell performance from "classical" materials than otherwise possible.
Vadim Oganesyan - Monday, November 18, 2013
Arthur Goetschy - Monday, November 25, 2013
ABSTRACT: The concepts of open and closed channels are useful to understand transport properties in disordered open media. We will review the physics of open channels and introduce a new random matrix ensemble that allows to predict the values of transmission or reflection achievable with wavefront shaping techniques in lossless or weakly absorbing media. This ensemble is parameterized by an effective fraction of controlled channels that we calculate microscopically. Its expression depends on the geometry (waveguide or slab), the illumination protocol (numerical aperture, size and shape of the illumination profile), and the long-range mesoscopic correlations of the medium. We will report measurements of the transmission eigenvalue density and of the total transmission in agreement with theoretical predictions. Finally, we will show that the same theoretical formalism can be used to predict the classical information capacity of a disordered medium as well as the effect of the disorder on the entanglement properties of a given input state of light.
Siddharth Dhomkar - Monday, December 2, 2013
Young Kim - Monday, December 9, 2013