David Kirkpatrick

September 9, 2010

Lasing nanoparticles around the room

Filed under: Science — Tags: , , , , , — David Kirkpatrick @ 1:30 pm

Via KurzweilAI.net — This is a pretty astounding feat.

From the link:

Researchers from Australian National University have developed the ability to move particles  over distances of up to 1.5 meters, using a hollow laser beam to trap light-absorbing particles in a “dark core.” The particles are then moved up and down the beam of light, which acts like an optical “pipeline.”

“When the small particles are trapped in this dark core very interesting things start to happen,” said Professor Andrei Rode. “As gravity, air currents, and random motions of air molecules around the particle push it out of the center, one side becomes illuminated by the laser while the other lies in darkness. This creates a tiny thrust, known as a photophoretic force that effectively pushes the particle back into the darkened core. In addition to the trapping effect, a portion of the energy from the beam and the resulting force pushes the particle along the hollow laser pipeline.”

Practical applications for this technology include directing and clustering nanoparticles in air, micro-manipulation of objects, sampling of atmospheric aerosols, and low-contamination/non-touch handling of sampling materials for transport of dangerous substances and microbes in small amounts, he said.

More info: Australian National University news

March 12, 2010

Carbon nanotube audio speakers

Lightweight, very thin and wireless when triggered with laser light. One interesting practical application is affixing a nanotube speaker to a surface rendering the entire surface acoustically active.

From the link:

The study confirms earlier research that carbon nanotubes that are stretched into sheets and electrically powered can produce intense , but researchers at UT Dallas’ Alan G. MacDiarmid NanoTech Institute have made some important advancements.

Although prior studies demonstrated that sheets of carbon nanotubes can produce sound when heated with alternating electrical current, the UT Dallas researchers have found that striking tones can be generated by vertical arrays of nanotubes, called forests, which resemble black velvet.

The team also discovered that high-quality sound can be generated when nanotube sheets or forests are struck with  that is modulated, or “altered,” in the acoustic frequency range.

And:

In addition to filling a room with sound from invisible speakers, nanotube speakers could easily cancel sound from the noisiest neighbor or dim the roar of traffic rushing past a neighborhood, using the same principles as current sound-canceling technologies.

“The sound generation by nanotube sheets can help to achieve this effect on very large scales,” Kozlov said.

March 2, 2010

Happy 50th birthday to the laser

Lasers are just cool, and now they have been for fifty years. Hit the link for photos and a thorough Technology Review history on controlling excited photons.

From the link:

This year is the 50th anniversary of the laser, a device used in applications from performing precise surgical procedures to measuring gravitational waves. In 1917, Albert Einstein proposed that a photon hitting an atom in a high energy state would cause the atom to release a second photon identical in frequency and direction to the first. In the 1950s, scientists searched for a way to achieve this stimulated emission and amplify it so that a group of excited atoms would release photons in a chain reaction. In 1959, American physicist Gordon Gould publicly used the term “light amplification by stimulated emission of radiation” for the first time. A year later, scientists demonstrated the first working optical laser.


Credit: HRL Laboratories

September 30, 2009

This is one fast optical transmission

Filed under: Science, Technology — Tags: , , , , — David Kirkpatrick @ 4:43 pm

Via KurzweilAI.net — Just wow.

Bell Labs breaks optical transmission record, 100 Petabit per second kilometer barrier

PhysOrg.com, Sept. 29, 2009

Bell Labs scientists have set a new optical transmission record of 15.5 Terabits per second over 7,000 kilometers, using 155 lasers, each operating at a different frequency and carrying 100 Gigabits/second of data.

The researchers also increased capacity by interfacing advanced digital signal processors with coherent detection, a new technology that makes it possible to effectively increase capacity by increasing the number oflight sources introduced into a single fiber yet still separate the light into its constituent colors when it reached its destination.

Read Original Article>>

July 3, 2009

Photonic computing

Filed under: Science, Technology — Tags: , , , , — David Kirkpatrick @ 3:16 pm

Via KurzweilAI.net — There’s a lot of research going on for a next generation computer that moves beyond transistors and silicon — quantum computing is probably the big cheese in the race — but the concept of laser-based computers might just be the most interesting, and in a space of very cool tech possibly the most interesting.

Laser light switch could leave transistors in the shade
NewScientist Tech, July 1, 2009

An optical transistor that uses one laser beam to control another could form the heart of a future generation of ultrafast photonic computers, overcoming the speed limits with wires, say Swiss researchers.

Using a green beam to switch an orange output beam from weak to strong is analogous to the way a transistor‘s control electrode switches a current between “on” and “off” voltages, and hence the 0s and 1s of digital data. And doing it with a single molecule means billions could be packed into future photonic chips.

 
Read Original Article>>

June 2, 2009

Making water run uphill …

… through lasers and nanostructures. Lots of possible apps here, plus it’s just freaking cool.

The release:

Scientists create metal that pumps liquid uphill

Ultra-fast laser makes metal that attracts, repels and guides liquids

IMAGE: Chunlei Guo uses the femtosecond laser (behind him) to create nanostructures in metal that can move liquid uphill.

Click here for more information. 

In nature, trees pull vast amounts of water from their roots up to their leaves hundreds of feet above the ground through capillary action, but now scientists at the University of Rochester have created a simple slab of metal that lifts liquid using the same principle—but does so at a speed that would make nature envious.

The metal, revealed in an upcoming issue of Applied Physics Letters, may prove invaluable in pumping microscopic amounts of liquid around a medical diagnostic chip, cooling a computer’s processor, or turning almost any simple metal into an anti-bacterial surface.

“We’re able to change the surface structure of almost any piece of metal so that we can control how liquid responds to it,” says Chunlei Guo, associate professor of optics at the University of Rochester. “We can even control the direction in which the liquid flows, or whether liquid flows at all.”

Guo and his assistant, Anatoliy Vorobyev, use an ultra-fast burst of laser light to change the surface of a metal, forming nanoscale and microscale pits, globules, and strands across the metal’s surface. The laser, called a femtosecond laser, produces pulses lasting only a few quadrillionths of a second—a femtosecond is to a second what a second is to about 32 million years. During its brief burst, Guo’s laser unleashes as much power as the entire electric grid of North America does, all focused onto a spot the size of a needlepoint, he says.

The wicking process, which on Guo’s metal moves at a quick one centimeter per second speed against gravity, is very similar to the phenomenon that pulls spilled milk into a paper towel or creates “tears of wine” in a wineglass—molecular attractions and evaporation combine to move a liquid against gravity, says Guo. Likewise, Guo’s nanostructures change the way molecules of a liquid interact with the molecules of the metal, allowing them to become more or less attracted to each other, depending on Guo’s settings. At a certain size, the metal nanostructures adhere more readily to the liquid’s molecules than the liquid’s molecules adhere to each other, causing the liquid to quickly spread out across the metal. Combined with the effects of evaporation as the liquid spreads, this molecular interaction creates the fast wicking effect in Guo’s metals.

Adding laser-etched channels into the metal further enhances Guo’s control of the liquid.

“Imagine a huge waterway system shrunk down onto a tiny chip, like the electronic circuit printed on a microprocessor, so we can perform chemical or biological work with a tiny bit of liquid,” says Guo. “Blood could precisely travel along a certain path to a sensor for disease diagnostics. With such a tiny system, a nurse wouldn’t need to draw a whole tube of blood for a test. A scratch on the skin might contain more than enough cells for a micro-analysis.”

Guo’s team has also created metal that reduces the attraction between water molecules and metal molecules, a phenomenon called hydrophobia. Since germs mostly consist of water, it’s all but impossible for them to grow on a hydrophobic surface, says Guo.

Currently, to alter an area of metal the size of a quarter takes 30 minutes or more, but Guo and Vorobyev are working on refining the technique to make it faster. Fortunately, despite the incredible intensity involved, the femtosecond laser can be powered by a simple wall outlet, meaning that when the process is refined, implementing it should be relatively simple.

Guo is also announcing this month in Physical Review Letters a femtosecond laser processing technique that can create incandescent light bulbs that use half as much energy, yet produce the same amount of light. In 2006, Guo’s team used the femtosecond laser to create metal with nanostructures that reflected almost no light at all, and in 2008 the team was able to tune the creation of nanostructures to reflect certain wavelengths of light—in effect turning almost any metal into almost any color.

 

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This research funded by the U.S. Air Force Office of Scientific Research and the National Science Foundation.

May 30, 2009

Solar cells and lasers

Filed under: Business, Science, Technology — Tags: , , , , , — David Kirkpatrick @ 12:15 pm

Here’s the latest news in solar — using lasers to improve solar cells.

The release:

Lasers are making solar cells competitive

Solar electricity has a future: It is renewable and available in unlimited quantities, and it does not produce any gases detrimental to the climate. Its only drawback right now is the price: the electric power currently being produced by solar cells in northern Europe must be subsidized if it is to compete against the household electricity generated by traditional power plants. At “Laser 2009″ in Munich, June 15 to 18, Fraunhofer researchers will be demonstrating how laser technology can contribute to optimizing the manufacturing costs and efficiency of solar cells. 

Cell phones, computers, MP3 players, kitchen stoves, and irons all have one thing in common: They need electricity. And in the future, more and more cars will also be fuelled by electric power. If the latest forecast from the World Energy Council WEC can be believed, global electricity requirements will double in the next 40 years. At the same time, prices for the dwindling resources of petroleum and natural gas are climbing.

“Rising energy prices are making alternative energy sources increasingly cost-effective. Sometime in the coming years, renewable energy sources, such as solar energy, will be competitive, even without subsidization,” explains Dr. Arnold Gillner, head of the microtechnology department at the Fraunhofer Institute for Laser Technology in Aachen, Germany. “Experts predict that grid parity will be achieved in a few years. This means that the costs and opportunities in the grid will be equal for solar electricity and conventionally generated household electricity.” Together with his team at the Fraunhofer Institute for Laser Technology ILT in Aachen, this researcher is developing technologies now that will allow faster, better, and cheaper production of solar cells in the future. “Lasers work quickly, precisely, and without contact. In other words, they are an ideal tool for manufacturing fragile solar cells. In fact, lasers are already being used in production today, but there is still considerable room for process optimization.” In addition to gradually improving the manufacturing technology, the physicists and engineers in Aachen are working with solar cell developers – for example, at the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg – on new engineering and design alternatives.

New production technologies allow new design alternatives

At “Laser 2009” in Munich, the researchers will be demonstrating how lasers can drill holes into silicon cells at breathtaking speed: The ILT laser system drills more than 3,000 holes within one second. Because it is not possible to move the laser source at this speed, the experts have developed optimized manufacturing systems which guide and focuses the light beam at the required points. “We are currently experimenting with various laser sources and optical systems,” Gillner explains. “Our goal is to increase the performance to 10,000 holes a second. This is the speed that must be reached in order to drill 10,000 to 20,000 holes into a wafer within the cycle time of the production machines.”

The tiny holes in the wafer – their diameter is only 50 micrometers – open up undreamt-of possibilities for the solar cell developers.  “Previously, the electrical contacts were arranged on the top of the cells. The holes make it possible to move the contacts to the back, with the advantage that the electrodes, which currently act as a dark grid to absorb light, disappear. And so the energy yield increases. The goal is a degree of efficiency of 20 percent% in industrially-produced emitter wrap-through (EWT) cells, with a yield of one-third more than classic silicon cells,” Gillner explains. The design principle itself remains unchanged: In the semi-conductor layer, light particles, or photons, produce negative electrons and positive holes, each of which then wanders to the oppositely poled electrodes. The contacts for anodes and cathodes in the EWT cells are all on the back, there is no shading caused by the electrodes, and the degree of efficiency increases. With this technique, it may one day be possible to use unpurified “dirty” silicon to manufacture solar cells that have poorer electrical properties, but that are cheaper. 

Drilling holes into silicon cells is only one of many laser applications in solar cell manufacturing. In the EU project Solasys – Next Generation Solar Cell and Module Laser Processing Systems – an international research team is currently developing new technologies that will allow production to be optimized in the future. ILT in Aachen is coordinating the six million euro project. “We are working on new methods that make the doping of semiconductors, the drilling and the surface structuring of silicon, the edge isolation of the cells, and the soldering of the modules more economical,” project coordinator Gillner explains. For example, “selective laser soldering” makes it possible to improve the rejection rates and quality of the contacting, and so reduce manufacturing costs. Until now, the electrodes were mechanically pressed onto the cells, and then heated in an oven. “But silicon cells often break during this process,” Gillner knows. “Breakage is a primary cost factor in production.” On the other hand, however, with “selective laser soldering” the contacts are pressed on to the cells with compressed air and then soldered with the laser. The mechanical stress approaches zero and the temperature can be precisely regulated. The result: Optimal contacts and almost no rejects.

Laser technology means more efficient thin film cells

Laser technology is also helping to optimize the manufacture of thin film solar cells. The extremely thin film packages made of semiconducting oxide, amorphous silicon, and metal that are deposited onto the glass panels still have a market share of only ten percent. But as Gillner knows, “This could be higher, because thin film solar cells can be used anywhere that non-transparent glass panels can be mounted, for example, on house facades or sound-insulating walls. But the degrees of efficiency are comparable low at five to eight percent, and the production costs are comparatively high.” The laser researchers are working to improve these costs. Until now, the manufacturers have used mechanical methods or solid-state lasers in the nanosecond range in order to structure the active layers on the glass panels. In order to produce electric connections between the semiconductor and the metal, grooves only a few micrometers wide must be created. At the Fraunhofer-Gesellschaft booth at “Laser 2009” the ILT researchers will be demonstrating a 400-watt ultrashort pulse laser that processes thin-film solar modules ten times faster than conventional diode-pumped solid-state lasers. “The ultrashort pulse laser is an ideal tool for ablating thin layers: It works very precisely, does not heat the material and, working with a pulse frequency of 80 MHz, can process a 2-by-3 meter glass panel in under two minutes,” Gillner reports. “The technology is still very new, and high-performance scanning systems and optical systems adapted to the process must be developed first. In the medium term, however, this technology will be able to reduce production costs.”

The rise of laser technology in solar technology is just taking off, and it still has a long way to go. “Lasers simplify and optimize the manufacture of classic silicon and thin-film cells, and they allow the development of new design alternatives,” Gillner continues. “And so laser technology is making an important contribution towards allowing renewable energy sources to penetrate further into the energy market.”

January 23, 2009

Nanoscale lasers and whispering galleries

Big breakthrough in tiny lasers — the apps here include lightening quick communications and data handling (photonics) and optical microchips.

The release:

Plasmonic whispering gallery microcavity paves the way to future nanolasers

The principle behind whispering galleries – where words spoken softly beneath a domed ceiling or in a vault can be clearly heard on the opposite side of the chamber – has been used to achieve what could prove to be a significant breakthrough in the miniaturization of lasers. Ultrasmall lasers, i.e., nanoscale, promise a wide variety of intriguing applications, including superfast communications and data handling (photonics), and optical microchips for instant and detailed chemical analyses.

 

Researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the California Institute of Technology have developed a “whispering gallery microcavity” based on plasmons – electromagnetic waves that race across the surfaces of metals. Such a plasmon wave has very small wavelength compared with the light, enabling the scaling down optical devices beyond diffraction limit of the light. Cavities are the confined spaces in lasers where light amplification takes place and this new micro-sized metallic cavity for plasmons improves on the quality of current plasmonic cavities by better than an order of magnitude.

“We have shown for the first time that metallic microcavities based on surface plasmons can have a large quality factor and can thereby enable ultra-small device fabrication and strong enhancement of the light,” said Xiang Zhang, a mechanical engineer who holds a joint appointment with Berkeley Lab’s Materials Sciences Division and the University of California (UC) Berkeley where he directs the NSF Nano-scale Science and Engineering Center.

“Plasmonic microcavities have uniquely different physical properties when compared to dielectric cavities and can extend microcavity research in entirely new ways, particularly at nanoscale dimensions,” said Kerry Vahala, a physics professor at Cal Tech and authority on photonic devices. “Our work shows that the full potential of this new class of device can be realized with careful design and material control.”

Zhang and Vahala led this collaborative research which is reported in the January 22, 2009 edition of the journal Nature. The paper is entitled: “High-Q surface-plasmon-polariton whispering-gallery microcavity.” In addition to Zhang and Vahala, other authors of the paper were Bumki Min, Eric Ostby, Volker Sorger, Erick Ulin-Avila and Lan Yang.

 

Surface Plasmons and Whispering Galleries

Just as the energy in waves of light is carried through space in discrete or quantized particle-like units called photons, so, too, is the energy in waves of charged gas (plasma) carried in quantized particle-like packets called plasmons, as they travel along metallic surfaces. When photons excite the collective electron oscillations at the interfaces between metal and dielectric (insulator) materials, they can form yet another quasi-particle called a surface plasmon polariton(SPP). Such polaritons play an important role in the optical properties of metals and can be used to manipulate light on a nanoscale.

“Metal-dielectric materials, also known as plasmonics, can be used to confine an optical field to a very small scale, much smaller than conventional insulators,” said Min, lead author on the Nature paper and former postdoctoral researcher in Zhang’s Lab, now an assistant professor at the Korea Advanced Institute of Science and Technology (KAIST). “This capability, often termed as breaking the light diffraction, is unobtainable with dielectric materials alone.”

The main obstacle to working with plasmonic materials for creating nanoscale lasers has been a low quality or “Q” factor, which is a measure of power loss in the lasing cavity – a laser cavity with a high-Q factor has a low power loss. Enter the whispering gallery phenomenon, which Cal Tech’s Vahala has used to boost the Q factor of dielectric microcavities. Whispering galleries are found in circular or elliptically shaped buildings, such as St. Paul’s Cathedral in London, where the phenomenon was first made famous, or Statuary Hall in the U.S. Capitol building.

The prevailing theory behind why whispering galleries work (first proposed in 1871 by British astronomer George Airy to explain St. Paul’s cathedral) is that sound originating at one point along the circumference of an enclosed sphere is reflected to another point along the circumference opposite the source. Vahala and his group applied this idea to dielectric microcavities, and Zhang and Min along with Ostby, Sorger and Ulin-Avila applied the idea to plasmonic microcavities.

 

“In these sphere-shaped microcavities, optical waves propagate in a similar way that sound waves propagate in a whispering gallery,” said Zhang. “They continue to circle around the edge of the cavity sphere and smoothness of the edge enhances or boosts the cavity’s Q factor.”

In this study, Zhang and his collaborators created a high-Q SPP whispering gallery microcavity by coating the surface of a high-Q silica microcavity with a thin layer of silver.

 

Explained Zhang, “Whenever light propagates in a metal it experiences some loss of power and this obviously reduces the performance of a device. Silver is the metal with the lowest loss, that is available.”

 

Whereas previous plasmonic microcavities achieved a best Q factor below 100, the whispering gallery plasmonic microcavity allows Q factors of 1,376 in the near infrared for SPP modes at room temperature.

 

“This nearly ideal value, which is close to the theoretical metal-loss-limited Q factor, is attributed to the suppression and minimization of radiation and scattering losses that are made possible by the geometrical structure and the fabrication method,” said Min, who believes that there is still room for plasmonic Q-factor improvement by geometrical and material optimizations.

Min said one of the first applications of the whispering gallery plasmonic microcavity is likely to be the development of a plasmonic nanolaser.

“To build a working laser, it is essential to have both the laser cavity (or resonator) and the gain media,” Min said.  “Therefore, we need a good, high-Q plasmonic microcavity to make a plasmonic nanolaser. Our work paves the way to accomplish the demonstration of a real plasmonic nanolaser.  In addition, fundamental research can also be pursued with this plasmonic cavity, such as the interaction of a single light emitter with plasmons.”

This work was supported by the U.S. Air Force Office of Scientific Research MURI program, and by the NSF Nanoscale Science and Engineering Center.

 

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our website at http://www.lbl.gov.

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