David Kirkpatrick

August 4, 2010

Invisibility cloak update

It’s been several months since I’ve come across any news on invisibility cloak technology, something of a pet subject around here, but here’s the very latest — findings on transformation optics.

From the second link, the release:

New findings promising for ‘transformation optics,’ cloaking

WEST LAFAYETTE, Ind. — Researchers have overcome a fundamental obstacle in using new “metamaterials” for radical advances in optical technologies, including ultra-powerful microscopes and computers and a possible invisibility cloak.

The metamaterials have been plagued by a major limitation: too much light is “lost,” or absorbed by metals such as silver and gold contained in the metamaterials, making them impractical for optical devices.

However, a Purdue University team has solved this hurdle, culminating three years of research based at the Birck Nanotechnology Center at the university’s Discovery Park.

“This finding is fundamental to the whole field of metamaterials,” said Vladimir M. Shalaev, Purdue’s Robert and Anne Burnett Professor of Electrical and Computer Engineering. “We showed that, in principle, it’s feasible to conquer losses and develop these materials for many applications.”

Research findings are detailed in a paper appearing on Aug. 5 in the journal Nature.

The material developed by Purdue researchers is made of a fishnet-like film containing holes about 100 nanometers in diameter and repeating layers of silver and aluminum oxide. The researchers etched away a portion of the aluminum oxide between silver layers and replaced it with a “gain medium” formed by a colored dye that can amplify light.

Other researchers have applied various gain media to the top of the fishnet film, but that approach does not produce sufficient amplification to overcome losses, Shalaev said.

Instead, the Purdue team found a way to place the dye between the two fishnet layers of silver, where the “local field” of light is far stronger than on the surface of the film, causing the gain medium to work 50 times more efficiently.

The approach was first developed by former Purdue doctoral student Hsiao-Kuan Yuan, now at Intel Corp., and it was further developed and applied by doctoral student Shumin Xiao.

Unlike natural materials, metamaterials are able to reduce the “index of refraction” to less than one or less than zero. Refraction occurs as electromagnetic waves, including light, bend when passing from one material into another. It causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside.

Being able to create materials with an index of refraction that’s negative or between one and zero promises a range of potential breakthroughs in a new field called transformation optics. Possible applications include a “planar hyperlens” that could make optical microscopes 10 times more powerful and able to see objects as small as DNA; advanced sensors; new types of “light concentrators” for more efficient solar collectors; computers and consumer electronics that use light instead of electronic signals to process information; and a cloak of invisibility.

Excitement about metamaterials has been tempered by the fact that too much light is absorbed by the materials. However, the new approach can dramatically reduce the “absorption coefficient,” or how much light and energy is lost, and might amplify the incident light so that the metamaterial becomes “active,” Shalaev said.

“What’s really important is that the absorption coefficient can be as small as only one-millionth of what it was before using our approach,” Shalaev said. “We can even have amplification of light instead of its absorption. Here, for the first time, we showed that metamaterials can have a negative refractive index and amplify light.”

The Nature paper was written by Xiao, senior research scientist Vladimir P. Drachev, principal research scientist Alexander V. Kildishev, doctoral student Xingjie Ni, postdoctoral fellow Uday K. Chettiar, Yuan, and Shalaev.

Fabricating the material was a major challenge, Shalaev said.

First, the researchers had to learn how to precisely remove as much as possible of the aluminum oxide layer in order to vacate space for dye without causing a collapse of the structure.

“You remove it almost completely but leave a little bit to act as pillars to support the structure, and then you spin coat the dye-doped polymer inside the structure,” he said.

The researchers also had to devise a way to deposit just the right amount of dye mixed with an epoxy between the silver layers of the perforated film.

“You can’t deposit too much dye and epoxy, which have a positive refractive index, but only a thin layer about 50 nanometers thick, or you lose the negative refraction,” Shalaev said.

Future work may involve creating a technology that uses an electrical source instead of a light source, like semiconductor lasers now in use, which would make them more practical for computer and electronics applications.

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The work was funded by the U.S. Army Research Office and the National Science Foundation.

Hit this link for the related image (it’s just too big for this blog and I didn’t feel like doing any resizing), and here’s the accompanying caption for the image:

This illustration shows the structure of a new device created by Purdue researchers to overcome a fundamental obstacle in using new “metamaterials” for radical advances in optical technologies, including ultrapowerful microscopes and computers and a possible invisibility cloak. The material developed by the researchers is a perforated, fishnet-like film made of repeating layers of silver and aluminum oxide. The researchers etched away a portion of the aluminum oxide between silver layers and replaced it with a “gain medium” to amplify light. (Birck Nanotechnology Center, Purdue University)

August 16, 2009

Nanolaser could lead to optical computer and more

Sounds promising. The field of alternate computation — such a quantum, optical, biological, et. al. — is always interesting.

The release:

New nanolaser key to future optical computers and technologies

Because the new device, called a “spaser,” is the first of its kind to emit visible light, it represents a critical component for possible future technologies based on “nanophotonic” circuitry, said Vladimir Shalaev, the Robert and Anne Burnett Professor of Electrical and Computer Engineering at Purdue University.

Such circuits will require a laser-light source, but current lasers can’t be made small enough to integrate them into electronic chips. Now researchers have overcome this obstacle, harnessing clouds of electrons called “surface plasmons,” instead of the photons that make up light, to create the tiny spasers.

Findings are detailed in a paper appearing online Sunday (Aug. 16) in the journal Nature, reporting on work conducted by researchers at Purdue, Norfolk State University and Cornell University.

Nanophotonics may usher in a host of radical advances, including powerful “hyperlenses” resulting in sensors and microscopes 10 times more powerful than today’s and able to see objects as small as DNA; computers and consumer electronics that use light instead of electronic signals to process information; and more efficient solar collectors.

“Here, we have demonstrated the feasibility of the most critical component – the nanolaser – essential for nanophotonics to become a practical technology,” Shalaev said.

The “spaser-based nanolasers” created in the research were spheres 44 nanometers, or billionths of a meter, in diameter – more than 1 million could fit inside a red blood cell. The spheres were fabricated at Cornell, with Norfolk State and Purdue performing the optical characterization needed to determine whether the devices behave as lasers.

The findings confirm work by physicists David Bergman at Tel Aviv University and Mark Stockman at Georgia State University, who first proposed the spaser concept in 2003.

“This work represents an important milestone that may prove to be the start of a revolution in nanophotonics, with applications in imaging and sensing at a scale that is much smaller than the wavelength of visible light,” said Timothy D. Sands, the Mary Jo and Robert L. Kirk Director of the Birck Nanotechnology Center in Purdue’s Discovery Park.

The spasers contain a gold core surrounded by a glasslike shell filled with green dye. When a light was shined on the spheres, plasmons generated by the gold core were amplified by the dye. The plasmons were then converted to photons of visible light, which was emitted as a laser.

Spaser stands for surface plasmon amplification by stimulated emission of radiation. To act like lasers, they require a “feedback system” that causes the surface plasmons to oscillate back and forth so that they gain power and can be emitted as light. Conventional lasers are limited in how small they can be made because this feedback component for photons, called an optical resonator, must be at least half the size of the wavelength of laser light.

The researchers, however, have overcome this hurdle by using not photons but surface plasmons, which enabled them to create a resonator 44 nanometers in diameter, or less than one-tenth the size of the 530-nanometer wavelength emitted by the spaser.

“It’s fitting that we have realized a breakthrough in laser technology as we are getting ready to celebrate the 50th anniversary of the invention of the laser,” Shalaev said.

The first working laser was demonstrated in 1960.

The research was conducted by Norfolk State researchers Mikhail A. Noginov, Guohua Zhu and Akeisha M. Belgrave; Purdue researchers Reuben M. Bakker, Shalaev and Evgenii E. Narimanov; and Cornell researchers Samantha Stout, Erik Herz, Teeraporn Suteewong and Ulrich B. Wiesner.

Future work may involve creating a spaser-based nanolaser that uses an electrical source instead of a light source, which would make them more practical for computer and electronics applications.

 

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The work was funded by the National Science Foundation and U.S. Army Research Office and is affiliated with the Birck Nanotechnology Center, the Center for Materials Research at Norfolk State, and Cornell’s Materials Science and Engineering Department.

IMAGE CAPTION:

Researchers have created the tiniest laser since its invention nearly 50 years ago. Because the new device, called a “spaser,” is the first of its kind to emit visible light, it represents a critical component for possible future technologies based on “nanophotonic” circuitry. The color diagram (a) shows the nanolaser’s design: a gold core surrounded by a glasslike shell filled with green dye. Scanning electron microscope images (b and c) show that the gold core and the thickness of the silica shell were about 14 nanometers and 15 nanometers, respectively. A simulation of the SPASER (d) shows the device emitting visible light with a wavelength of 525 nanometers. (Birck Nanotechnology Center, Purdue University)

A publication-quality image is available at http://news.uns.purdue.edu/images/+2009/shalaev-spasers.jpg

Abstract on the research in this release is available at: http://news.uns.purdue.edu/x/2009b/090817ShalaevSpasers.html

STORY AND PHOTO CAN BE FOUND AT:

http://news.uns.purdue.edu/x/2009b/090817ShalaevSpasers.html

January 22, 2009

Gel rocket fuel

Okay, this has now become a release dump but I couldn’t resist this story. It’s just that cool

The release:

January 21, 2009

Researchers cooking up new gelled rocket fuels

WEST LAFAYETTE, Ind. –

Testing gelled
rocket fuels
Download photo

caption below

Engineers and food scientists are teaming up to develop a new type of gelled fuel the consistency of orange marmalade designed to improve the safety, performance and range of rockets for space and military applications.

“This is a very multidisciplinary project,” said Stephen Heister, the Purdue University professor of aeronautics and astronautics who is leading one of two teams on the project, which is funded by the U.S. Army Research Office.

 

Gels are inherently safer than liquids because they don’t leak, and they also would allow the military to better control rockets than is possible with solid fuels now used. Motors running on gelled fuels could be throttled up and down and controlled more precisely than conventional rockets that use solid propellants, Heister said.

“You can turn the engine on and off, you can coast, go fast or slow,” he said. “You have much greater control, which means more range for missiles. The gelled propellants also tend to have a little more energy than the solid propellants.”

Gelled fuels also could be used in thrusters to position satellites and on NASA space missions.

The team includes researchers from mechanical engineering, aeronautics and astronautics, food science, and agricultural and biological engineering at Purdue, as well as researchers from Iowa State University and University of Massachusetts.

Paul Sojka, a professor of mechanical engineering and an associate director of the project, is building an experiment to take high-speed videos of the gelatinous fuel’s behavior. Jets of the gel form during the fuel-injection process.

“These jets are wiggling, there are pulsations, and those pulsations, we believe, lead to the formation of specific spray patterns and droplet formation,” Sojka said. “The fluid mechanics of gels are quite challenging. The viscous properties of the gel change depending on how fast it’s flowing, which is not true of common liquids such as water or gasoline.”

The project will tap the expertise of food scientists and food engineers, who are accustomed to working with gels, said Carlos Corvalan, an associate professor of food science.

“Gels are more complex than ordinary solids and fluids,” Corvalan said. “Fluids are characterized by viscosity, and solids are characterized by elasticity. Because gels share properties of both solids and fluids, they possess viscoelastic properties, or a combination of both.”

Food science and agricultural engineering researchers will study these viscoelastic properties and create simulations describing how the gels behave.

The five-year, $6.4 million “spray and combustion of gelled hypergolic propellants” project is a U.S. Army Multidisciplinary University Research Initiative, or MURI. Another team is led by Pennsylvania State University.

Future rockets could require that gelled propellants be sprayed by fuel injectors into a motor’s combustion chamber at rates of thousands of pounds per second. Using the gelled propellants, however, will require a thorough knowledge of how the fuel breaks into droplets as it is being sprayed into the chamber.

The fuels are hypergolic, meaning they require no ignition source but ignite spontaneously when mixed with an oxidizer. The fuel and oxidizer tanks each feed into a separate fuel injector. As the streams of fuel and oxidizer mix, they form droplets that ignite.

“There is an unsteadiness of these two jets, and these fluctuations can have all sorts of ramifications in terms of engine performance,” said Sojka, who specializes in research to learn what happens between the fuel and oxidizer streams as they form elliptical sheets, spaghetti-like strands and droplets.

The high-speed movies are recorded at about 10,000 frames per second, or roughly 300 times faster than the typical video signal.

The collision of fuel and oxidizer jets causes “impact waves.”

“We are trying to understand the source of those waves and be able to control or capitalize on the unsteadiness to make smooth combustion,” Heister said.

Purdue faculty members and graduate students are conducting experiments at the university’s Maurice J. Zucrow Laboratories, in the Department of Food Science and in the School of Agricultural and Biological Engineering aimed at developing a comprehensive spray model that describes the precise behavior of propellant droplets in a rocket motor.

One aim is to be able to consistently create the relatively small, uniform droplets that would be needed for rocket propulsion. Food scientists are familiar with processes used to create droplets in foods.

“The texture of those foods is closely associated with the average size and range of sizes of droplets,” said Osvaldo Campanella, a professor of agricultural and biological engineering. “In a combustion chamber you also want to control droplet size, but for a different reason – to precisely control combustion. You want uniform combustion, and for that you need controlled drop size.”

Corvalan will lead work to develop simulations that determine the viscoelastic behavior of the gels and droplets.

Researchers will first work with water-based gels that simulate fuels and will eventually conduct experiments using actual propellants.

“It’s kind of like orange marmalade without the rind,” Heister said. “We are going to make this gel and push it through holes and study how it flows and how big the drops are. Eventually we’ll study the real gelled fuels, which can be quite hazardous and reactive, so we will use them in small quantities and under tightly controlled conditions.”

The viscoelastic properties of the gels will not only be experimentally measured, but molecular models representing the gels also will be developed as part of research in Purdue’s Department of Chemistry. The models will enable researchers to predict the behavior of gels and optimize their formulations.

Information from experiments and modeling will be used to design systems that have improved combustion.

Timothee Pourpoint, a research assistant professor of aeronautics and astronautics, is in charge of setting up and maintaining a propulsion lab to test the fuels at Zucrow. Because the fuels being tested are toxic, the lab will be equipped with a specialized ventilation system. Pourpoint conducted extensive research on hypergolic fuels for his doctoral thesis at Purdue.

 

PHOTO CAPTION:
Timothee Pourpoint, a research assistant professor of aeronautics and astronautics, is in charge of designing and operating a new Purdue lab to test gelled rocket fuels that have the consistency of orange marmalade. The fuels are designed to improve the safety, performance and range of rockets for space and military applications, and the research will involve a team of engineers and food scientists. Standing in the new lab are, from left, Tim Phillips and Mark James, both graduate students in aeronautics and astronautics, Pourpoint and Travis Kubal, a graduate student in mechanical engineering. (Purdue News Service photo/Andrew Hancock)