Contacts:                                                                    For Release: Jan. 16, 2014
Jigang Wang, Ames Laboratory, 515-294-5630
Breehan Gerleman Lucchesi, Public Affairs, 515-294-9750

Scientists at the U.S. Department of Energy's Ames Laboratory have demonstrated broadband terahertz (THz) wave generation using metamaterials. The discovery may help develop noninvasive imaging and sensing, and make possible THz-speed information communication, processing and storage. The results appeared in the Jan. 8 issue of Nature Communications.

Terahertz electromagnetic waves occupy a middle ground between electronics waves, like microwave and radio waves, and photonics waves, such as infrared and UV waves. Potentially, THz waves may accelerate telecom technologies and break new ground in understanding the fundamental properties of photonics. Challenges related to efficiently generating and detecting THz waves has primarily limited their use.

Traditional methods seek to either compress oscillating waves from the electronic range or stretch waves from the optical range. But when compressing waves, the THz frequency becomes too high to be generated and detected by conventional electronic devices. So, this approach normally requires either a large-scale electron accelerator facility or highly electrically-biased photoconductive antennas that produce only a narrow range of waves.

To stretch optical waves, most techniques include mixing two laser frequencies inside an inorganic or organic crystal. However, the natural properties of these crystals result in low efficiency.

So, to address these challenges, the Ames Laboratory team looked outside natural materials for a possible solution. They used man-made materials called metamaterials, which exhibit optical and magnetic properties not found in nature.

Costas Soukoulis, an Ames Laboratory physicist and expert in designing metamaterials, along with collaborators at Karlsruhe

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A THz spectrometer driven by femtosecond laser pulses was used to demonstrate THz emission from a split-ring resonator metamaterial
of single nanometer thickness.

Institute of Technology in Germany, created a metamaterial made up of a special type of meta-atom called split-ring resonators. Split-ring resonators, because of their u-shaped design, display a strong magnetic response to any desired frequency waves in the THz to infrared spectrum.

Image A team led by Ames Laboratory physicists demonstrated broadband, gapless terahertz emission (red line) from split-ring resonator metamaterials (background) in the telecomm wavelength. The THz emission spectra exhibit significant enhancement at magnetic-dipole resonance of the metamaterials emitter (shown in inset image). This approach has potential to generate gapless spectrum covering the entire THz band, which is key to developing practical THz technologies and to exploring fundamental understanding of optics.

Ames Laboratory physicist Jigang Wang, who specializes in ultra-fast laser spectroscopy, designed the femto-second laser experiment to demonstrate THz emission from the metamaterial of a single nanometer thickness.

“The combination of ultra-short laser pulses with the unique and unusual  properties of the metamaterial generates efficient and broadband THz waves from emitters of significantly reduced thickness,” says Wang, who is also an associate professor of Physics and Astronomy at Iowa State University.

The team demonstrated their technique using the wavelength used by telecommunications (1.5 microns), but Wang says that the THz generation can be tailored simply by tuning the size of the meta-atoms in the metamaterial.

“In principle, we can expand this technique to cover the entire THz range,” said Soukoulis, who is also a Distinguished Professor of physics and astronomy at Iowa State University.

What’s more, the team’s metamaterial THz emitter measured only 40 nanometers and performed as well as traditional emitters that are thousands of times thicker.

“Our approach provides a potential solution to bridge the ‘THz technology gap’ by solving the four key challenges in the THz emitter technology:  efficiency; broadband spectrum; compact size; and tunability,” said Wang.

Soukoulis, Wang, Liang Luo and Thomas Koschny's work at Ames Laboratory was supported by the U.S. Department of Energy's Office of Science. Wang's work is partially supported by Ames Laboratory’s Laboratory Directed Research and Development (LDRD) funding.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.

Ames Laboratory is a U.S. Department of Energy Office of Science national laboratory operated by Iowa State University. Ames Laboratory creates innovative materials, technologies and energy solutions. We use our expertise, unique capabilities and interdisciplinary collaborations to solve global problems.


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Inquiry 2013, Issue 2

Welcome to 
Inquiry 2013Issue 2

The Cutting-Edge Technology at The Ames Laboratory

ImageMaterials characterization has always been a hallmark of the Ames Laboratory. Determining a material’s specific properties – its crystal structure, electrical and magnetic properties, how it moves through various phases – gives scientists a better understanding of why it performs or behaves in a certain way and allows them to predict how other materials may behave in similar or different manners.
Obviously, the better we’re able to measure those characteristics, the more accurate and predictive our theoretical descriptions can be. And while Ames Lab scientists have excelled at characterizing new materials and developing new techniques, the Lab is on the  verge of taking a giant step forward in its characterization capabilities.

(Click on issue cover for full pdf)

In this issue of Inquiry, we take a look a several of those characterization technologies from the ability to grow single crystals with previously unattainable compositions and advanced nuclear magnetic resonance capabilities to a new facility to house the next generation of ultra-sensitive electron microscopes and the grand opening of the Critical Materials Institute.

 

 

Director's Message

Awards

East meets Midwest

New era in research - Critical Materials Institute

Shhhh! New facility to shelter delicate instruments from outside interference

Growing single crystals under pressure

Using defects in diamond to probe magnetic properties at the nanoscale

Cutting edge NMR technology

Ames Lab interns make their research mark

Director's Message 2013-2

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Materials characterization has always been a hallmark of the Ames Laboratory. Determining a material’s specific properties – its crystal structure, electrical and magnetic properties, how it moves through various phases – gives scientists a better understanding of why it performs or behaves in a certain way and allows them to predict how other materials may behave in similar or different manners.
Obviously, the better we’re able to measure those characteristics, the more accurate and predictive our theoretical descriptions can be. And while Ames Lab scientists have excelled at characterizing new materials and developing new techniques, the Lab is on the  verge of taking a giant step forward in its characterization capabilities.
One cutting-edge advancement will be the construction of the new Sensitive Instrument Facility. Scheduled to be built beginning the spring of 2014, the SIF will be a state-of-the-art building designed specifically to provide an isolated environment for atomic-scale electron microscopes so sensitive that the breathing or heartbeat of the operator can distort the image of the specimen under study. You can read about this unique facility on page 8 of this issue.
Ruslan Prozorov is spearheading an effort to enhance our capabilities for studying the magnetic properties of nanoscale materials. As you might imagine, as the sample size diminishes, greater sensitivity is required of the equipment used to characterize its properties.  Prozorov is developing a new piece of equipment that utilizes a defect in the crystal structure of diamond to create a highly sensitive probe for measuring the magnetic field of nano-particles down to the level of a single electron. Find out more about this work on page 14.
Similarly, Marek Pruski is leading an effort to enhance the Lab’s nuclear magnetic resonance (NMR) with the addition of a dynamic nuclear polarization-NMR spectrometer. DNP-NMR uses microwaves to polarize electrons, and then transfers that polarization from the electrons to the nuclei of the sample being analyzed, an enhancement of anywhere from eight to 30 times in signal sensitivity. Results that used to take a week to obtain will now take hours or minutes.  Turn to page 16 to find out more about this effort.
The Lab has also excelled at producing some of the best single crystals, in part because the Materials Preparation Center provides the best raw materials. But the recent acquisition of a new crystal-growth furnace now allows us to grow crystals at elevated pressure, letting us incorporate materials that were too volatile for traditional methods. Take a closer look on page 12.
Finally, we hosted the ribbon-cutting ceremony for the Critical Materials Institute in September. As one of DOE’s Energy Innovation Hubs, the CMI marks a major effort to reduce or eliminate material criticality for our nation. By establishing a team comprised of top researchers from national labs, research universities and industry, the CMI hopes to focus the combined resources to quickly and efficiently solve the problem of potential shortages of the materials vital to high-tech, clean-energy technologies. We hope that our efforts will soon bear fruit as we strive to quickly move solutions from the lab bench to the marketplace.

 

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Tom Lograsso, Interim Director

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