Spring 2007 Colloquium

Speaker:

Robert Byer , Stanford University

Title:

LIGO and LISA:  The Search for Gravitational Waves

Host:

Stanley Pau

Abstract:

Einstein formulated the general theory of relativity near 100 years ago and showed that gravity is curvature in space-time and further that ripples in space-time, gravitational waves, travel at the speed of light.  Today the Laser Interferometer Gravitational Wave Observatory (LIGO) project is using ground based 4km long interferometers to search for gravitational waves.  The progress for LIGO and other earth based gravitational wave interferometers will be reviewed.

 During the summer of 2005 the Laser Interferometer in Space Antenna, LISA, a project joint between NASA and ESA met to discuss the designs of the space-based, 5-million kilometer long LISA interferometer, its sensitivity and the gravitational wave sources that are to be observed.  LISA, the first great observatory in the NASA Beyond Einstein program, is scheduled for launch in 2015.

 The detection of gravitational waves requires the ultimate in precision measurement.  The ‘ruler’ used to detect oscillations in space-time is the constant; the speed of light.  The light source is a very stable Nd:YAG solid state laser that is pumped by laser diode arrays demonstrated at Stanford University in 1984.

Speaker:

William D. Phillips, National institute of Standards and Technology

Title:

A Bose Condensate in an Optical Lattice:  Cold Atomic Gases Meet Solid State Physics

Host:

Poul Jessen

Abstract:

An atomic-gas Bose-Einstein Condensate, placed in the periodic light-shift potential of an optical standing wave, exhibits many features that are similar to the familiar problem of electrons moving in the periodic potential of a solid-state crystal lattice. Among the differences are that the BEC represents a wavefunction whose coherence extends over the entire lattice, with what is essentially a single quasi momentum and that the lattice potential can be turned on and off, modulated,  or accelerated through space.   Experiments that are not easily done with solids are often straightforward with optical lattices, sometimes with surprising results.

Speaker:

Donald C. O'Shea, Professor Emeritus Georgia Institute of Technology and Editor of Optical Engineering

Title:

Teaching, Simulations, and Teaching Simulations

Host:

Jose Sasian

Abstract:

Speaker:

Nicolaas Bloembergen, University of Arizona College of Optical Sciences, Nobel Laureate in Physics, 1981

Title:

From Millisecond to Attosecond Laser Pulses

Host:

Stanley Pau

Abstract:

The history of the development of ever shorter laser pulses is reviewed.The first laser demonstrated by Maiman in 1960 using  a ruby crystal pumped by a flash lamp had an irregular light output of about a millisecond duration.Hellwarth introduced Q-switching in 1961 to obtain pulses shorter than one microsecond.Passsive Q-switching with a saturable absorber yielded pulses shorter than a nanosecond in 1965.Refinements in this method opened up the picosecond and femtosecond regime.The use of reactive Q-switching by intensity-dependent self-focusing in TI-sapphire has made femtosecond pulse generators widely available.  The attosecond regime is being explored during the past ten years.Since these pulses are shorter than the duration of one cycle of visible light,they are based based on extreme nonlinear optical effects of ionization by tunneling,high harmonic generation by recollision and control of the amplitude and the field- envelope phase of the originating femtosecond pulse.

Speaker:

Axel Scherer, California Institute of Technology

Title:

Microfabricated Photonic Devices

Hosts:

Nasser Peyghambarian and Galina Khitrova

Abstract:

Over the past 30 years, microfabrication techniques have improved to enable the control of structural dimensions to below 100nm. This exquisite capability driven in large part by the needs of the microelectronics industry, has led to the opportunity to define optical devices with predictable performance and reproducibility. In this presentation, some of the potential applications of this opportunity and the resulting "microfabricated optics" will be described. Examples of silicon CMOS photonics for inexpensive data communications systems, suspended disk and photonic crystal nanocavities for ultra-small light sources, and replication molded lasers and optofluidic devices will be described.

Finally, different light concentration methods, such as the use of surface plasmon and photonic crystal devices will be compared with more conventional refractive index confinement of light in small cavities. Some applications of such devices in the area of biotechnology will be described.

Speaker:

Jon Mooney, Solid State Scientific Corporation

Title:

Spectral Imaging and Pseudoimaging with Slitless Prismatic Sensors

Host:

Eustace Dereniak

Abstract:

Spectral image sensors are an attractive alternative to high spatial resolution sensors in applications where spectral discriminants are present and the spatial resolution required for conventional target detection leads to an aperture that is prohibitively large.  When the spectral discriminants are strong the case for spectral imaging can be compelling.  Unfortunately, spectral imagers suffer from the expanded sampling needed to simultaneously acquire the spatial and spectral information.  The sampling is further complicated by difficulties encountered in mapping the the three-dimensional spectral object onto the two-dimensional focal plane array.  A wide variety of spectral imaging architectures and techniques have been developed to address this mapping.

Here we explore slitless prism based sensor architectures.  Slitless Prismatic Image Sensors treat the mapping from three dimensions down to two dimensions as a tomographic projection and use computational techniques to reconstruct the spectral image.  Pseudoimaging sensors detect the target signature in the projection data without reconstructing the spectral image.  Pseodoimaging is effective for detection and identification of surprise and uncued flash events in cluttered backgrounds.

Speaker:

Scott Tyo, College of Optical Sciences, University of Arizona

Title:

Sensing Higher Order Image Information at the Focal Plane Array

Host:

Stanley Pau

Abstract:

Spectral and polarimetric imagery have emerged as tools that can assist in a range of sensing applications.  In many cases, it is desired to create a spatial image where either the spectrum or polarization (or both!) are measured at every pixel across a scene.  Numerous strategies have been suggested that enable such data to be measured, and each strategy has its own drawbacks.  One class of sensing strategy that has applicability in certain scenarios could be termed integrative sensing.  In these methods, the focal plane array itself is specially designed to inherently sense the information that is sought after.  This talk will discuss two efforts to accomplish this, one for polarimetry and one for spectral imagery.  For the past several years, we have been working with the Air Force Research Lab to operate a LWIR, division of focal plane, imaging polarimeter.  This device integrates an array of micropolarizers with a HgCdTe detector to create an inherently polarization sensitive device.  The advantages of the system is that the data is inherently aligned, both mechanically and temporally.  The disadvantage is that neighboring pixels - each viewing a different polarization state - have different instantaneous fields of view.  This IFOV error leads to false polarization signatures, especially near edges within the image.  I will discuss our efforts towards calibration of this system and compensation for the errors, and will present a range of imagery data indicating the utility of the system.  In our second effort, we are developing electronically-tunable IR FPAs for spectral sensing.  We have developed IR photodetectors based on nanoscale, self-assembled quantum dots.  These dots are grown in a quantum well, providing a number of parameters that can be used to tailor the potential contour.  Through the use of asymmetry, these devices can be made to have a spectral responsivity that changes as a function of the bias voltage applied across the detector.  We have developed noise-tolerant postprocessing strategies that allow us to infer spectral information by taking multiple measurements of a scene at different biases.  The advantage of such a system over conventional spectral sensors include: 1) the biases can be chosen at the time of collection, making the system adaptive; 2) the biases should be switchable at video frame rate; 3) the system can operate as a broadband thermal imager, a two-color camera, or in a multispectral mode without changing any hardware on the system.

Speaker:

Demitrios Christodoulides, University of Central Florida

Title:

Discrete Nonlinear Optics

Host:

Ewan Wright

Abstract:

In this talk we provide an overview of recent developments in the area of discrete nonlinear optics. Nonlinear interactions in discrete optical structures can lead to a host of new phenomena including for example optical solitons and vortices, nonlinear surface waves, and new modes of instability. Experimental results concerning these effects in Kerr, quadratic and photorefractive lattices will be presented. The possibility of scaling these arrays at nano-dimensions will be discussed.

Speaker:

Neal Armstrong, University of Arizona

Title:

Organic Solar Cells and Related Technologies -- It's All About Interfaces

Host:

Nasser Peyghambarian

Abstract:

This talk will review some of our recent efforts to understand and control the interfacial issues which limit the power conversion efficiency of organic solar cells, and related hybrid technologies.  We'll briefly review the essential elements of energy conversion in these thin film technologies, and then show examples of three technological platforms that we have been involved in recently: a) thin film biomimetic photosynthesis platforms (a collaboration led by Saavedra et.al.), b) thin film solar hydrogen platforms using semiconductor nanoparticles as the photoelectrocatalyst (collaboration with Pyun, Zheng and McGrath), and then c) spend the bulk of our time on planar heterojunction cells using common organic dyes (collaboration with Marder, Kippelen of the STC).  In all three cases, the chemical characterization and modification of the semi-transparent platform (ITO and related transparent oxides) is critical to the performance of the solar cell.

Speaker:

Roger Angel, University of Arizona

Title:

Optics to Mitigate Global Warming

Host:

Jose Sasian

Abstract:

China puts into operation one 1 GW coal fired power station every week.  To make a significant impact on global warming, photovoltaic systems to harvest 5 square miles of sunlight would have to be built every week.  Architectural float glass is already made at more than this rate, and could be turned into lens or mirror arrays.  Concentration at ~ 1000 suns would allow photovoltaic cell area to be reduced by the same factor.  Transmission of solar (and wind) power across continents and the globe is needed for 24 hour cover.  Ground lines or microwave space links are both possible solutions.

Speaker:

Connie Chang-Hasnain, University of California at Berkeley

Title:

Nano-Optoelectronics for Communications

Host:

Nasser Peyghambarian

Abstract:

In this talk, I will like to provide an overview of some of the projects we are working on.  Specifically, I will talk about two projects, III-V nanowire on Si and high-index contrast grating VCSEL.  Heterogeneous integration of optoelectronic active devices (diode lasers) with CMOS integrated circuits (IC) has been a subject of great interest for a couple of decades.  But solutions remained to be illusive.  The key bottleneck has been process incompatibility of the two types of material systems.  In this talk, we discuss the synthesis and characterization of III-V nanowires onto a Si substrate at low growth temperature in the range of 380~450 C using MOCVD.  The small dimension of nanowires (diameter <20 nm) enables low defect growth of active region despite a large lattice mismatch.  The low temperature growth and the large-scale manufacturability of an MOCVD system make this approach very promising.  Finally, I will discuss a VCSEL incorporating a novel high-index contrast subwavelength grating.  The HCG is less than 0.23 um thick, can provide very high reflectivity and wide bandwidth.  By integrating a movable, single-layer HCG as the VCSEL top mirror, single mode emission (SMSR >40 dB) and continuous wavelength tuning (~2.5 nm) was obtained at room temperature under CW operation. The small footprint of HCG enables the scaling down of each of the cantilever dimensions by a factor of 10, leading to 1000 times reduction in mass and increase in the mechanical resonant frequency.  Hence, a NEMO tunable VCSEL with tuning speed in the GHz range can be potentially realized.

Speaker:

Richard Ziolkowski, University of Arizona

Title:

Metamaterial-Enabled Resonant Electrically-Small Scattering and Radiating Systems in the Microwave and Optical Regimes

Host:

Scott Tyo

Abstract:

There continues to be a great desire for high performance electrically small radiating and scattering systems from the microwave to the optical regimes whose physical characteristics and electromagnetic responses could be tailored to satisfy a wide range of applications.  Metamaterials, artificial materials whose electromagnetic responses can in principle be engineered to any negative or positive value, have been shown recently to be a potential enabling technology for these radiating and scattering systems.   Traditional electrically small radiating and scattering systems are poor transducers of their input or excitation energy. Several metamaterial-based configurations have been demonstrated recently that significantly improve the radiating and scattering performance characteristics of these systems.  The resulting systems are resonant despite being significantly sub-wavelength in size.  For instance, an electrically-small epsilon-negative (ENG) or double negative (DNG) spherical shell surrounding an electrically-small dipole antenna can be designed to act as an effective distributed inductor that is properly matched to the capacitive electric dipole element to form a naturally resonant LC structure, as well as to act as a resistive matching element to the source. Thus, an overall efficiency of 100% can be achieved in such an electrically-small radiating system.   The reciprocal configuration, plane wave scattering from an electrically-small ENG or DNG metamaterial-coated sphere, has been shown to exhibit unity scattering. Moreover, by introducing gain media, the effects of losses and dispersion can be controlled. For instance, lasing has been demonstrated at visible wavelengths in an electrically-small metal coated nano-particle.  A review of the progress to date on all of these resonant metamaterial-based electrically small radiating and scattering systems, and their potential practical microwave and optical realizations will be given. The effects of losses and dispersion will be emphasized in the discussion.