Saturday, September 18, 2010


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A team of McGill chemists have discovered that a technique known as photoacoustic infrared spectroscopy could be used to identify the composition of pigments used in art work that is decades or even centuries old. Pigments give artist's materials colour, and they emit sounds when light is shone on them.

"The chemical composition of pigments is important to know, because it enables museums and restorers to know how the paints will react to sunlight and temperature changes," explained Dr. Ian Butler, lead researcher and professor at McGill's Department of Chemistry. Without a full understanding of the chemicals involved in artworks, preservation attempts can sometimes lead to more damage than would occur by just simply leaving the works untreated.

Photoacoustic infrared spectroscopy is based on Alexander Graham Bell's 1880 discovery that showed solids could emit sounds when exposed to sunlight, infrared radiation or ultraviolet radiation. Advances in mathematics and computers have enabled chemists to apply the phenomenon to various materials, but the Butler's team is the first to use it to analyze typical inorganic pigments that most artists use.

The researchers have classified 12 historically prominent pigments by the infrared spectra they exhibit – i.e., the range of noises they produce – and they hope the technique will be used to establish a pigment database. "Once such a database has been established, the technique may become routine in the arsenal of art forensic laboratories," Butler said. The next steps will be to identify partners interested in developing standard practices that would enable this technique to be used with artwork.



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In 2009, newly installed photovoltaic (PV) cells world-wide produced a peak amount of electricity estimated at 7.4 GW, out of which 5.8 GW was located in Europe. Similarly to previous years, this shows the EU's dominance, where more than three quarters of the world's new solar systems were installed. By the end of 2009, Europe's cumulative installed PV electricity generation capacity (existing and newly installed) was 16 GW, which is about 70% of the world's total (22GW). These are just some of the findings of the ninth annual Photovoltaics Status Report published by the European Commission's Joint Research Centre (JRC).

The study, carried out by the JRC's Institute for Energy (IE), summarises and evaluates the results of a survey of more than 300 companies worldwide. It looks at the photovoltaic market and industry worldwide with special attention to the EU, India, Japan, China, Taiwan and the United States, providing a final outlook on the topic. It also provides an overview of current activities in research, manufacturing and market implementation in this sector. However, data from 2009 may have a higher uncertainty than usual, mostly due to the difficult market situation and a decreased willingness of companies to report confidential data.

It is estimated that one GW of PV electricity generation capacity provides enough electricity for about 250,000 European households during one year. In the EU in 2009, 27.5 GW of new power capacity was constructed. About 21% (5.8 GW, up from 5.1 GW in 2008) of this was PV based.

Most of the EU's growth that year occurred in Germany (3.8 GW, reaching a cumulative value of 9.8 GW), where in the 4th quarter, some 2.3 GW were connected to the grid. In fact, Germany ranks first in the world for cumulative installed capacity (9.8 GW), followed by Spain (3.5 GW), thanks to the renewable energy legislation in these countries.

Second in the PV growth ranking was Italy with 0.73 GW (cumulative 1.2 GW), followed by Japan: 0.48 GW (2.6 GW), the US: 0.46 GW (1.65 GW), the Czech Republic: 0.41 GW (0.46 GW) and Belgium: 0.3 GW (0.36 GW).

However, the PV market is still incipient. In the EU, only 0.4% of total supplied electricity came from PV in 2009. In the world, this percentage is a mere 0.1%.

When it comes to the production of PV cells, the report estimates that this has increased worldwide to 11.5 GW in 2009 (56% up from 2008). In the EU, it remained at 2 GW (1.9 GW in 2008).

Leaders in this field were China with 4.4 GW in 2009 as compared to 2.4 GW in 2008, Taiwan (1.6 GW and 0.8 GW respectively) and Malaysia, whose production grew from 0.16 GW to 0.72 GW.

A significant number of players announced a reduction or cancellation of their plans to expand PV production worldwide in 2008 and 2009. Nevertheless, the shortfall appears to have been compensated, even exceeded, by new entrants into the field – notably large semiconductor or energy-related companies.

A special feature shown in 2009 is the fact that changes in the market - which has moved from a supply- to a demand-driven logic - and the resulting over capacity for solar modules have caused a dramatic price reduction of almost 50% over 2 years, with an average selling price of less than €1.5 per Watt.

Other key findings of the report:

* Wafer-based silicon is still the main technology for solar cells and represented 80% of the market share in 2009.
* The market share of thin-film solar products has increased from 6% in 2005 and 10% in 2007 to 16-20% in 2009.
* Concentrating photovoltaics (which uses lenses to concentrate sunlight on to photovoltaic cells) is an emerging technology growing at a fast pace, although from a low starting point.
* The existing photovoltaic technology mix is a solid foundation for future growth of the sector, as no single technology can satisfy all the different consumer needs. The variety of photovoltaic technologies is an insurance against a "roadblock" for the implementation of solar photovoltaic electricity if material limitations or technical obstacles restrict the further development or growth of a single technology pathway.

European Commission's Joint Research Centre


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A tiny optical device built into a silicon chip has achieved the slowest light propagation on a chip to date, reducing the speed of light by a factor of 1,200 in a study reported in Nature Photonics (published online September 5 and in the November print issue).

The ability to control light pulses on an integrated chip-based platform is a major step toward the realization of all-optical quantum communication networks, with potentially vast improvements in ultra-low-power performance. Holger Schmidt, professor of electrical engineering in the Baskin School of Engineering at the University of California, Santa Cruz, leads the team of researchers at UC Santa Cruz and Brigham Young University that developed the new device.

"Slow light and other quantum coherence effects have been known for quite awhile, but in order to use them in practical applications we have to be able to implement them on a platform that can be mass-produced and will work at room temperature or higher, and that's what our chips accomplish," Schmidt said.

Whereas optical fibers routinely transmit data at light speed, routing and data processing operations still require converting light signals to electronic signals. All-optical data processing will require compact, reliable devices that can slow, store, and process light pulses.

"The simplest example of how slow light can be used is to provide a data buffer or tunable signal delay in an optical network, but we are looking beyond that with our integrated photonic chip," Schmidt said.

The device relies on quantum interference effects in a rubidium vapor inside a hollow-core optical waveguide that is built into a silicon chip using standard manufacturing techniques. It builds on earlier work by Schmidt and his collaborators that enabled them to perform atomic spectroscopy on a chip ( The first author of the new paper is Bin Wu, a graduate student in electrical engineering at UCSC. The coauthors include John Hulbert, Evan Lunt, Katie Hurd, and Aaron Hawkins of Brigham Young University.

Several different techniques have been used to slow light to a crawl and even bring it to a complete halt for a few hundredths of a millisecond. Previously, however, systems based on quantum interference required low temperatures or laboratory setups too elaborate for practical use. In 2008, researchers at NTT Laboratories in Japan developed a specially structured silicon chip that could slow light pulses by a factor of 170. Called a photonic crystal waveguide, it has advantages for certain applications, but it does not produce the quantum effects of the atomic spectroscopy chip developed by Schmidt's group.

Those quantum effects produce not only slow light but other interactions between light and matter that raise the possibility of radically new optical devices for quantum computing and quantum communication systems, according to Schmidt. In addition, the system makes it easy to turn the effect on and off and tune it to the desired speed of light.

"By changing the power of a control laser, we can change the speed of light--just by turning the power control knob," he said.

The control laser modifies the optical properties of the rubidium vapor in the hollow-core waveguide. Under the combined action of two laser fields (control and signal), electrons in the rubidium atoms are transferred into a coherent superposition of two quantum states. In the strange world of quantum physics, they exist in two different states at the same time. One result is an effect known as electromagnetically induced transparency, which is key to producing slow light.

"Normally, the rubidium vapor absorbs the light from the signal laser, so nothing gets through. Then you turn on the control laser and boom, the material becomes transparent and the signal pulse not only makes it through, but it also moves significantly more slowly," Schmidt said.

This study is the first demonstration of electromagnetically induced transparency and slow light on a fully self-contained atomic spectroscopy chip.

"This has implications for looking at nonlinear optical effects beyond slow light," Schmidt said. "We can potentially use this to create all-optical switches, single-photon detectors, quantum memory devices, and other exciting possibilities."

(Photo: C. Lagattuta)

UC Santa Cruz




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