Thousands of Sensors to Keep Watch on Earth's Climate
Science is only as good as the data on which it is based, the saying goes. To help meet the forecasting challenges of climate-change science, the U.S. National Ecological Observatory Network (NEON) plans an ambitious network of more than 45,000 sensors to monitor climate indicators such as temperature, precipitation, carbon dioxide concentration, and soil characteristics. Researchers will present a strategy for automating and managing this vast array of climate sentinels.
Presentation JWE16, "The National Ecological Observatory Network's Fundamental Instrument Unit: Challenges to Managing Thousands of Environmental Sensors," by Jeffrey R. Taylor, Ed Ayres, Hongyan
Looking for CO2 Leaks
One proposed method to slow anthropogenic climate change is to capture carbon dioxide emissions and store them underground. But the solution won't work if the CO2 escapes. Researchers have designed and tested an imaging system that may be able to spot leaks by the telltale way the CO2 feeds vegetation growth.
Presentation EThB6,"A field-deployable multi-spectral imaging system for indirect CO2 leak detection through vegetation imaging," by Justin A. Hogan and Joseph A. Shaw, Montana State University, takes place Thursday, Nov. 3 at 11:45 a.m.
Let the Sunshine In
Natural light is free and aesthetically pleasing, but it can't reach basements or windowless offices. Novel daylighting systems, called core sunlighting, that bring light into these building areas might solve this problem by piping the sunshine through cost-effective, mirror-lined tubes.
Presentation EThD2, "Using sunlight for affordable indoor illumination," by Lorne A. Whitehead, University of British Columbia, takes place Thursday, Nov. 3 at 5 p.m.
Studying Space Debris: NASA Uses Optics to Help Reveal Size, Composition of Space Junk
NASA is using new optical techniques to study the ever-growing cloud of space debris encircling the Earth. The Soviets first flung a human-made object into orbit in 1957, and after more than 50 years of space-going enterprises by many different nations, it's starting to get crowded up there. Space debris poses risks to satellites, spacecraft, and spacewalking astronauts. Recognizing the dangers of a collision, NASA has been monitoring space debris for more than 25 years. Known bits of space junk, such as large, defunct satellites, can be tracked, but there may be thousands more pieces of small debris littering near-Earth space. NASA researchers will summarize new efforts to identify and characterize this space "pollution." The NASA Orbital Debris Program Office uses telescopes to peer into the night sky and capture images of the faint glint of space junk as it reflects the Sun's rays. Scientists can estimate an object's diameter based on the brightness of the shine. NASA researchers also perform experiments in the lab to measure how an object's mass, size, material composition, and spatial orientation change the way it reflects light. Using these base measurements, the researchers have identified space debris observed by their telescopes as possible solar panel fragments or sheets of multi-layered insulation. NASA uses the information it gathers to help develop space debris mitigation standards and collision avoidance maneuvers for spacecraft, making space a little safer.
Presentation JWE14, "Observations of Human-made Debris in Earth Orbit," by Heather Cowardin, NASA, takes place Wednesday, Nov. 2 at 6 p.m.
Novel LED Design May Boost Efficiencies
Light-emitting diodes (LEDs) are vastly more efficient than incandescent light bulbs and even compact fluorescent bulbs, but they still have design constraints that limit their potential. Current systems rely on scattering and diffraction of light from within an LED device to boost the total light emitted. This design enables extraction efficiencies of approximately 50 percent in some red-yellow LEDs and approximately 80 percent in some blue-green LEDs. This technique of producing multiple reflections of light within the device, however, may have reached its limits. A new technique proposed by Xue-Lun Wang and his colleagues at the National Institute of Advanced Industrial Science and Technology (AIST) in Japan takes a more direct approach and may pave the way to even more efficient LEDs. The researchers designed a flat-top, ridge-shaped semiconductor surface that channels two waves of energy toward the top of the semiconductor. Known as evanescent waves, these waves travel along the surface/air interface of the semiconductor. When they intersect and combine at the ridge top, they couple with each other and are transformed efficiently into light. By adding an additional layer of silicon dioxide to the semiconductor, the light extraction efficiencies can be enhanced even further. Their initial results indicate that the ridge-shaped design is 10 to 16 times more efficient than a flat design. By using this technique, the researchers were able to extract light without involving the multiple reflection processes in conventional techniques. Their next step is to combine the system with a metal mirror in hope of creating efficiencies much higher than those in conventional devices.
Presentation SDThB5, "A Novel LED Light Extraction Technique Based on Evanescent Wave Coupling." Xue-Lun Wang, Guo-Dong Hao, and Tokio Takahashi, Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan, takes place Thursday, Nov. 3 at 12 p.m.
'Inverted Pyramid' Design Makes Thinner Wafers, Cheaper Solar Cells
The battle between solar power and fossil fuels can be fought on many fronts, but a big one is cost. Researchers from the Massachusetts Institute of Technology (MIT) in Cambridge, Mass., have designed a prototype silicon solar cell that promises to be just as efficient as a standard silicon cell, but that uses much less material, making it theoretically cheaper to produce. Typically, solar cells capture sunlight using crystalline silicon (c-Si) wafers 100 to 300 micrometers thick, two to six times the thickness of a single human hair. But the c-Si material is expensive and accounts for a significant portion of a cell's fabrication costs. The MIT team started with c-Si wafers that were 10 times thinner than the typical wafers – just 10 micrometers thick. To make them absorb light efficiently, the scientists etched a series of regularly spaced inverted pyramids, each one less than a micrometer wide, into the surface of the wafers. When the researchers tested the structure's ability to absorb the frequencies of light emanating from the Sun, they found that their prototype matched the light-absorbing abilities of much thicker structures. Furthermore, they say, the manufacturing methods used to etch the tiny inverted pyramids into the wafers are simple, well-established, and inexpensive. According to the researchers, solar cells need to be more than two times less expensive than they currently are in order to compete with fossil fuels in terms of cost.
Presentation PThB3 "Efficient Light-trapping in Periodic Nanostructured Thin Crystalline Silicon Solar Cells," by Gang Chen, MIT, takes place Thursday, Nov. 3 at 11 a.m.
'Power Droop' Challenges of LEDs for High-power Lighting
The United States is currently in a transition from old and familiar incandescent light bulbs to vastly more efficient solid-state LEDs, or light emitting diodes. There remain, however, formidable challenges facing LED technologies, particularly when trying to use them for high-power lighting applications. One of the major hurdles is the so-called "efficiency droop" that occurs when attempting to ramp up LEDs to high current densities. Researchers from Rensselaer Polytechnic Institute in New York will discuss the origin of this droop as well as ways to reduce it.
Presentation JThA4, "Promises and Challenges in Light-emitting Diodes for High-power Lighting Applications," by E. Fred Schubert and Jaehee Cho, Rensselaer Polytechnic Institute, takes place Thursday, Nov. 3 at 9:30 a.m.
Toward a Simpler White Organic LED Design
Organic light emitting diodes (OLEDs), because of their remarkable efficiency and low-energy consumption, show great promise in meeting home and business lighting needs. One of the remaining hurdles to deploying these more broadly, however, is the challenge of producing white light, which is currently generated through a complex design that combines multiple color emitters. Research is underway to develop an efficient white OLED that uses a single, broadband emitter.
Presentation SDWB1, "High Efficiency White Organic Light Emitting Device Using a Single Emitter," by Jian Li, Arizona State University, Tempe , takes place Wednesday, Nov. 2 at 10:30 a.m.
Improving Efficiency with Photonic Crystal Sandwiches
"Tandem" solar cells can increase energy efficiency by combining multiple materials that absorb different frequencies of light. But they are difficult to manufacture because only certain materials are compatible, and minor defects can have a major impact on the ability of two adjacent materials to work together. Researchers in Germany have discovered that 3-D photonic crystals sandwiched between two different absorbing materials can manage the flow of photons within a tandem solar cell, preventing one material from interfering with the light-absorbing abilities of the other, and making it easier to manufacture tandem solar cells on a large scale.
Presentation PWB4 ,"3D photonic crystal as intermediate reflector layer in micromorph tandem cells," by R.B. Wehrspohn, J. Üpping, A. Bielawny, Martin Luther University Halle, Institute of Physics, Germany, takes place Wednesday , Nov. 2 at 12 p.m.
Plasmonics for Better Light Trapping
In their quest for more efficient sunlight-to-energy converters, scientists are exploring the light-controlling properties of metals in the burgeoning field of plasmonics, which examines the flow of a special type of light wave along the surface of metals. Stanford University materials scientist Mark Brongersma will discuss recent progress in the development of plasmonic and other nano-sized structures that can increase the efficiency of light absorption and trapping in solar cells.
Presentation PWD1, "Plasmonic and High Dielectric Constant Nanostructures for Light Trapping," by Mark Brongersma, Stanford University, takes place Wednesday, Nov. 2 at 4:30 p.m.
The Renewable Energy & the Environment: OSA Optics and Photonics Congress provides a forum where speakers present the latest results in the energy/environment arena ranging from solar energy research to photovoltaic applications. This Congress is composed of four complimentary co-located meetings dealing with the most recent, high-impact optical advances in the Energy and Environment areas:
Optics & Photonics Congresses (OPCs) are clusters of new and established topical meetings in order to bring together leaders among communities within optics. Congresses are designed to retain the collegial settings of OSA topical meetings and provide richer experiences for networking, information sharing and discussion across the disciplines of optical science and engineering. They also offer opportunities for more special events including plenary sessions, symposia, short courses and joint exhibits. Scientists who attend the topical meeting of their discipline will not only have the opportunity to network with colleagues within their own field but can also learn more about other fields.
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