A THz spectrometer driven by femtosecond laser pulses was used to demonstrate THz emission from a split-ring resonator metamaterial of single nanometer thickness http://phys.org/news/2014-01-highly-efficient-broadband-terahertz-metamaterials.html#jCp
by Breehan Gerleman Lucchesi
(Phys.org)
—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 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.
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.
More information: "Broadband terahertz generation from
metamaterials." Liang Luo, Ioannis Chatzakis, Jigang Wang, Fabian B. P.
Niesler, Martin Wegener, Thomas Koschny, Costas M. Soukoulis. Nature Communications 5, Article number: 3055 DOI: 10.1038/ncomms4055. Received 05 August 2013 Accepted
03 December 2013 Published 08 January 2014
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