Colloquium

April 27, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Tom Krupenkin, Bell Laboratories Lucent Technologies, will present Manipulating Liquids on the Tunable Nanostructured Surfaces.  Abstract:  An ability to manipulate microscopic volumes of liquids with the high precision becomes increasingly important with the recent progress in micro- and nanofluidics and its rapid penetration in various industrial applications. Dynamic control over the interaction of liquids with the solid substrate constitutes a very important aspect of this problem. Nanostructured solid surfaces offer a promising way to achieve this goal. In this talk we discuss recently demonstrated dynamically tunable nanostructured surfaces. The behavior of these surfaces can be reversibly switched between superhydrophobic and hydrophilic states by the application of electrical voltage and current. The proposed approach potentially allows novel methods of manipulating microscopically small volumes of liquids. This includes almost frictionless liquid transport, the ability to precisely control droplet shape and position, as well as dynamic control over the penetration on liquids through the nanostructured layer.  The obtained results potentially open new and exciting opportunities in optofluidics, thermal management of microelectronics, chemical microreactors, bio/chemical lab-on-a-chip devices, and many other areas.

April 20, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Paul K.L. Yu, University of California at San Diego Department of Electrical and Computer Engineering, will present Advances in Photonic Devices for Analog Fiber Link Applications.  Robert Norwood is the faculty host.  Abstract:  This presentation gives an overview of the requirements of the photonic components in their insertion in analog applications such as CATV, antenna remoting and base station connections in wireless communication systems. While the driving force for their use is bandwidth, the eventual limiting factors would be cost, performance, and reliability. The presentation reviews the advances in the state-of-the-art photonics devices such as laser diodes, high power lasers, external modulators, and photodetectors. In particular, electroabsorption waveguide modulators made of bulk semiconductors or multiple quantum wells have been considered for analog link applications. Its modulation and absorption properties have been used for dual function applications, which also influenced their optimization for these operations. Comparisons will also be made regarding the direct modulation scheme versus the external modulation scheme.

April 13, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Kristina M. Johnson, Duke University Engineering Department Professor and Dean, will present Applications of Liquid Crystals to Optical Information Processing  Projection Display.  Nasser Peyghambarian is the faculty host. 

April 6, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Ursula J. Gibson, former OSC faculty member now with Dartmouth College, will present Protein Crystals in Optical Tweezers.  Nasser Peyghambarian is the faculty host.  Abstract:  Momentum transfer from light to small particles can be used to overcome Brownian motion, trapping them with a tightly focused beam.  If the particle is anisotropic, in either its shape or optical properties, the orientation of the particle can also be controlled.  Lysozyme crystals are birefringent and have a highly reproducible morphology, with an aspect ratio that can be varied as a function of growth conditions. They thus represent an opportunity for a detailed study of the relative importance of the shape and optical anisotropy.  Growth of high quality protein crystals is important for structural biology studies, and we have explored the use of tweezers for growth of lysozyme from seeds.  Optical trapping has been reported for polymer molecules on the order of the size of some globular proteins, which suggests that it may be possible to nucleate a crystal in a chosen location, away from the walls of the container.  Preliminary experiments in this direction will be described.

March 30, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Demetri Psaltis, California Institute of Technology, will present Optofluidics.  Abstract:  Optofluidics refers to a class of adaptive optical circuits that integrate optical and fluidic devices. Familiar examples include liquid crystals and dye lasers. The introduction of liquids in the optical structure enables flexible fine-tuning and reconfiguration of circuits so they can perform tasks optimally in a changing environment. Dr. Demetri Psaltis will discuss how the emergence of fluidic transport technologies at the micron and nanometer levels opens possibilities for novel adaptive optical devices.  Approaches that Caltech researchers are pursuing include the integration of microfluidic circuits with photonic structures that contain voids into which fluids are injected and  the use of colloidal solutions of nanoparticles. Electrical fields or light beams redistribute the nanoparticles and modify the optical properties of the structure. Liquid dyes injected into microfluidic chips provide the optical gain necessary for building a dye laser on a chip.

March 23, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Urs Utzinger, University of Arizona Departments of Biomedical Engineering, Obstetrics and Gynecology, Electrical and Computer Engineering, BIO5 Institute for Collaborative Bioresearch, and Optical Sciences, will present Optical Spectroscopy and Imaging for Ovarian Cancer Diagnosis.  Abstract: Early detection would significantly improve survival and quality of life of women at increased risk to develop ovarian cancer. Endogenous fluorescence spectroscopy in the UV-C and UV-A excitation range shows correlation with disease state. Cell culture experiments support that alterations in UV-C fluorescence signatures relate to proliferation or protein production and UV-A signatures to oxidative metabolism. Non-linear microscopy techniques can determine intrinsic tissue signatures related to cellular redox state and extracellular collagen architecture and allow us to understand the origin of bulk tissue fluorescence. Clinical systems based on multispectral imaging might guide physicians with the in-situ assessment of pathologies and could provide a monitoring tool for women at increased risk to develop ovarian cancer.

March 9, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Zakaya H. Kafafi, Naval Research Laboratory, Washington, D.C., will present Tailored Materials and Interfaces for Organic Optoelectronics.  Nasser Peyghambarian is the OSC faculty host.  Abstract:  The 21st century is witnessing a revolution in the area of electronics and photonics. Conventional semiconductor technology is being challenged by potentially inexpensive, flexible, and light-weight organic electronic and photonic devices. Achieving high efficiency and stability in these devices necessitates the design and development of  electro- and photo-active materials with the desired chemical, physical, electronic and optical properties.  Different approaches taken for tuning the electronic structures of fluorescent, carrier-transporting, and light-harvesting materials through molecularly engineered materials and tailored interfaces will be reviewed. For instance, designing guest and host molecules with the proper energy gaps for the active emissive layer of an organic light-emitting diode (OLED) is critical for efficient energy transfer from host to guest molecules and/or direct electron-hole recombination on the emitting guest. Maximizing the separation between the highest occupied molecular orbital (HOMO) energy level of an electron donor relative to that of the lowest unoccupied molecular orbital (LUMO) of an electron acceptor is necessary for creating a large built-in chemical potential at the donor/acceptor interfaces. The latter will result in efficient charge separation of the exciton(s) in the light-harvesting layer(s) of an organic photovoltaic cell and a large open circuit voltage. Tailoring the organic/metal and organic/polymer interfaces (ex. the HOMO and LUMO levels of the organics relative to the work functions of the anode and cathode, respectively) is necessary for good energy level alignment and efficient charge injection at these contacts. Using these strategies, we developed OLEDs with electroluminescence quantum efficiencies close to the theoretical limit. The talk will give an overview of how these concepts are put together to design molecular semiconductors and devices with enhanced performance.

March 2, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Daniel Lopez, Bell Labs Lucent Technologies, will present MEMS Based Spatial light Modulators: Technology and Applications.  Stanley Pau is the OSC faculty host.  Abstract:  Micro Electro Mechanical Systems (MEMS) technology have been used for miniaturization of conventional opto-mechanical components, gaining in speed and cost while maintaining good optical performance for a variety of applications. More importantly, MEMS allow integration of a very large number of independently controlled mechanical elements into a single microsystem, enabling radically new functionality. In the optical domain, MEMS Spatial Light Modulators (SLM) having hundreds to millions of separate spatially distributed degrees of freedom have been realized for projection, telecom switching, spectral power equalization, adaptive optics, spectroscopy and a host of other applications. MEMS SLMs are the key components in optical systems ranging from High Definition Televisions to telescopes, and have potential to radically change many others. This talk will review some of these applications and corresponding established and emerging MEMS SLM technology and MEMS design principles.

February 23, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Dr. Eric Van Stryland, Optical Sciences alumnus and Dean of the College of Optics and Photonics: CREOL & FPCE at the University of Central Florida, will present Nonlinear Optical Spectroscopy: absorption and refraction.  Nasser Peyghambarian is the host.  Abstract:  We have been developing a number of spectroscopic methods for accurately measuring the nonlinear absorption spectrum along with the dispersion of the nonlinear refraction of optical materials from semiconductors to organic dyes.  These methods include the 'standard' Z-scan, femtosecond pump/continuum probe spectroscopy, and more recently a femtosecond white-light continuum Z-scan.   The Z-scan is a simple method that can simultaneously measure both the sign and magnitude of the nonlinear absorption and nonlinear refraction with interferometric sensitivity. The Z-scan techniques yield the frequency degenerate spectra (equal photon energies) while the pump/probe method gives the nondegenerate nonlinearities which allows for nonlinear Kramers-Kronig relations between refraction and absorption (even though Kramers-Kronig relations normally come from linear dispersion theory). We will show a variety of examples of spectra along with some scaling laws for semiconductors

February 16, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Iam-Choon Khoo, Pennsylvania State University Electrical Engineering Department, will present Liquid Crystal for Extreme Nonlinear Optics and Tunable Optics.  Nasser Peyghambarian is the host.  Abstract:  The mesophases of liquid crystals are characterized by the extreme sensitivities of their crystalline axis to external perturbation, resulting in perhaps the largest light scattering abilities of all known materials. We will review how these fundamental physical properties lead to a nonlinear refractive index coefficient that could exceed 1000 cm2/W, i.e. a trillion times that of CS2 and how such extreme nonlinear optical response could lead to novel applications in optical switches and image processing devices. More recently, liquid crystals based tunable photonic crystals and negative index planar nanostructures have also been demonstrated. 

February 9, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Susan Houde-Walter, CEO of LaserMax, is the scheduled speaker.  Jim Wyant is the host.  Dr. Houde-Walter's presentation is titled HOW BIG IS YOUR YAM? And other important factors in your career path.  Abstract:  A strong technical education is necessary, but perhaps not sufficient, for a successful career in optics.  After traveling around the world, teaching in academia and working in industry, we offer a few unsolicited tips for optimizing your career path, both before and after graduation.  From the 2005 OSA Student Leadership Prize talk.

February 6, 2006 -- Special Presentation -- 10:00 to 11:30 a.m. -- Ventana Room, Student Union
Professor Sir Michael V. Berry, Bristol University Physics Department, will present Conical Diffraction: Imaging Hamilton's Diabolical Point.  Abstract:  The transformation of a narrow beam into a hollow cone when incident along the optic axis of a biaxial crystal, predicted by Hamilton in 1832, created a sensation when observed by Lloyd soon afterwards. It was the prototype of the conical intersections now popular in quantum chemistry. But the fine structure of the light cone contains many subtle features, slowly revealed by experiment, whose definitive explanation, involving new mathematical asymptotics, has been achieved only recently, along with definitive experimental test of the theory. Radically different phenomena, being intensively studied now, arise when chirality and absorption are incorporated in addition to biaxiality.

February 2, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
Alex K-Y Jen, University of Washington Department of Materials Science & Engineering and Department of Chemistry, will present Exceptional Photonic and Optoelectronic Properties Through Molecular Design and Controlled Self-Assembly.  Abstract:  We recently introduced new dendritic structures to nonlinear optical (NLO) chromophores and polymers to investigate their effects on enhancing poling efficiency and alignment stability of these materials.  Our aim is to tune their molecular topology systematically at nanoscale to minimize the strong intermolecular electrostatic forces between the large chromophore dipoles.  Compared to the conventional organic NLO materials, this nanoscale architectural control approach provides a great opportunity to simultaneously optimize macroscopic electro-optic activity, thermal stability, and optical loss.  In this talk, the latest progress in design, synthesis, and E-O properties of these molecular-engineered systems will be discussed.  Specifically, the material systems ranging from fully-functionalized dendrimers with an NLO chromophore as the core and crosslinkable groups on the periphery and novel dendron-coil block copolymers will be highlighted.  By applying these nanoscale architectural control concepts and manipulations, we have recently achieved unprecedented E-O activity (> 300 pm/V @1310nm) of these materials (the E-O coefficient is one order higher than the state-of-the-art inorganic material, LiNbO3).  This successful development of these materials will launch a new paradigm for next generation high-performance photonic materials and devices.  In addition to the study on NLO materials, our recent results in molecular electronics will also be highlighted. We have developed a design criterion for functional conjugated molecules with controllable molecular architectures. The size, shape, orientation and ordered patterns of molecular wires or switches on inorganic substrates can be engineered through a delicate interplay of the intermolecular p-p stacking, hydrogen bonding, and chemisorptive substrate-linker interactions. The ability to assemble predictable two-dimensional molecular crystals and understand the order-related electronic behavior of single molecular components may allow us to design a platform for further miniaturization of electronic devices.

January 26, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
John Sipe, University of Toronto Department of Physics, will present Optical Injection of Spin Currents.  Abstract:  It has been understood for years that spin polarized currents in semiconductors can be generated by optically injecting spin polarized carriers and then dragging them with a bias voltage.  But only recently has it been generally appreciated, and observed experimentally, that the direct optical injection of spin currents is possible.  Here the currents appear on the time scale of the injecting pulse or pulses, which typically is on the order of only 100 femtoseconds.  Particularly interesting are scenarios where pure spin currents are injected, in which there is no net spin or electrical current generated, but rather there is a “sorting” of injected carriers by their spin, with carriers of one spin sent in one direction and those of the opposite in the other.  I will review our theoretical calculation of these effects, and some of the experimental results of our collaborators, Professor Henry van Driel at the University of Toronto and Professor Arthur Smirl at the University of Iowa.  Rolf Binder is the host.

January 19, 2006 -- Optical Sciences Colloquium -- 3:45 p.m. -- Meinel 408/410
E. Fred Schubert, Rensselaer Polytechnic Institute, will present Innovations in Light Emitting Diodes for Solid-State and Smart Lighting Applications.  Stanley Pau is the host.