Communication technologies including smartphones and laptops could now be 1,000 times faster, new study suggests

 Many of the communication tools of today rely on the function of light or, more specifically, on applying information to a light wave. Up until now, studies on electronic and optical devices with materials that are the foundations of modern electronics -- such as radio, TV, and computers -- have generally relied on nonlinear optical effects, producing devices whose bandwidth has been limited to the gigahertz (GHz) frequency region. (Hertz stands for cycles per second of a periodic phenomenon, in this case 1billion cycles).

Thanks to research performed at the University of Pittsburgh, a physical basis for terahertz bandwidth (THz, or 1 trillion cycles per second) -- the portion of the electromagnetic spectrum between infrared and microwave light -- has now been demonstrated.

In a paper published March 4 in Nature Photonics, Hrvoje Petek, a professor of physics and chemistry in Pitt's Kenneth P. Dietrich School of Arts and Sciences, and his colleague Muneaki Hase, a professor of applied physics at the University of Tsukuba in Japan and a visiting scientist in Petek's lab, detail their success in generating a frequency comb -- dividing a single color of light into a series of evenly spaced spectral lines for a variety of uses -- that spans a more than 100 terahertz bandwidth by exciting a coherent collective of atomic motions in a semiconductor silicon crystal.

"The ability to modulate light with such a bandwidth could increase the amount of information carried by more than 1,000 times when compared to the volume carried with today's technologies," says Petek. "Needless to say, this has been a long-awaited discovery in the field."

To investigate the optical properties of a silicon crystal, Petek and his team investigated the change in reflectivity after excitation with an intense laser pulse. Following the excitation, the team observed that the amount of reflected light oscillates at 15.6 THz, the highest mechanical frequency of atoms within a silicon lattice. This oscillation caused additional change in the absorption and reflection of light, multiplying the fundamental oscillation frequency by up to seven times to generate the comb of frequencies extending beyond 100 THz. Petek and his team were able to observe the production of such a comb of frequencies from a crystalline solid for the first time.

"Although we expected to see the oscillation at 15.6 THz, we did not realize that its excitation could change the properties of silicon in such dramatic fashion," says Petek. "The discovery was both the result of developing unique instrumentation and incisive analysis by the team members."

Petek notes the team's achievements are the result of developing experimental and theoretical tools to better understand how electrons and atoms interact in solids under intense optical excitation and of the invested interest by Pitt's Dietrich School in advanced instrumentation and laboratory infrastructure.

The team is currently investigating the coherent oscillation of electrons, which could further extend the ability of harnessing light-matter interactions from the terahertz- to the petahertz-frequency range. Petahertz is a unit of measure for very fast frequencies (1 quadrillion hertz).

This research was funded by a grant from the National Science Foundation.

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The above story is reprinted from materials provided by University of Pittsburgh.

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Journal Reference:

Muneaki Hase, Masayuki Katsuragawa, Anca Monia Constantinescu, Hrvoje Petek. Frequency comb generation at terahertz frequencies by coherent phonon excitation in silicon. Nature Photonics, 2012; DOI: 10.1038/nphoton.2012.35

Hydrogen cartridges fuel laptops and phones for outdoor enthusiasts

 How does a Michigan State University scientist fuel his enthusiasm for chemistry after 60 years? By discovering a new energy source, of course.

This week, SiGNa Chemistry Inc. unveiled its new hydrogen cartridges, which provide energy to fuel cells designed to recharge cell phones, laptops and GPS units. The green power source is geared toward outdoor enthusiasts as well as residents of the Third World, where electricity in homes is considered a luxury.

The spark for this groundbreaking technology came from the laboratory of James Dye, SiGNa's co-founder and University Distinguished Professor of Chemistry Emeritus at MSU. His work with alkali metals led to a green process to harness the power of sodium silicide, which is the source for SiGNa's new product.

"In our lab, we were able to produce alkali metal silicides, which basically are made from sodium and silicon, which, in turn, are produced from salt and sand," Dye said. "By adding water to sodium silicide, we're able to produce hydrogen, which creates energy for fuel cells. The byproduct, sodium silicate, is also green. It's the same stuff found in toothpaste."

SiGNa was able to build on Dye's research and develop a power platform that produces low-pressure hydrogen gas on demand, convert it to electricity via a low-cost fuel cell and emit simple water vapor.

Dye, director of SiGNa's scientific council, said that making the jump to research the company's products was a small one.

"I've been working with alkali metals for 50 years," he said. "My research was closely related to what SiGNa was looking for. So when they came to me with their idea, it was a relatively easy adaptation to make."

Using a similar process, Dye was able to assist the creation of a fuel source to power electric bicycles. The fuel cell, developed by SiGNa's partners, ranges in size from 1 watt to 3 kilowatts and is capable of pushing a bicycle up to 25 mph for approximately 100 miles.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Michigan State University.