Photonics: strong vibrations

May 10, 2012 By Eugene Low
Terahertz (THz) generation. A strong THz emission from the center of the device is observed in the tip-to-tip design (top). The electrodes are the black lines in the center of the device. The colours show the electric field from low (blue) to high (red) values. Much weaker electric fields and THz emission are seen in the interdigitated electrode design (bottom). Credit: From Ref. 1 © 2012 H. Tanoto

A new approach to generating terahertz radiation will lead to new imaging and sensing applications. The low energy of the radiation means that it can pass through materials that are otherwise opaque, opening up uses in imaging and sensing — for example, in new security scanners. In practice, however, applications have been difficult to implement.

Terahertz (THz) electromagnetic has promising properties for a wide range of applications. The of the radiation means that it can pass through materials that are otherwise opaque, opening up uses in imaging and sensing — for example, in new security scanners. In practice, however, applications have been difficult to implement. radiation is a difficult portion of the electromagnetic spectrum to utilize. The frequencies of the region are higher than the mega and gigahertz frequencies achievable with conventional electronic circuits, but are too low-frequency to be compatible with optical instruments.

“The key challenges for THz technology are the development of a compact high power source and high sensitivity detector operating at room temperature,” explains Jinghua Teng of the A*STAR Institute of Materials Research and Engineering. A recent discovery made by Teng’s team of a new, efficient protocol for THz wave generation that utilizes the enhancement of light between nanometer-scale electrical contacts may provide a solution.

One method for creating continuous THz radiation involves directing two optical laser beams of almost similar frequencies at a suitable nonlinear material, such as certain semiconductors causing light emission exactly at the frequency difference of the two laser beams. If this difference is sufficiently small, the radiation produced falls within the THz spectrum.

However, this process is rather inefficient and requires strong light fields. Fortunately, strong amplification of light can occur near small metallic objects that act as mini antennas. This antenna effect occurs with the small metal contacts that are needed to link the non-linear material that creates the THz emission — in the current case a variant of the common semiconductor gallium arsenide.

Normally, these electrical contacts are arranged such that they resemble the fingers of interlocked hands reaching into each other. However, the A*STAR researchers developed a revised design in which the electrodes are arranged tip to tip (see top of the above image). This means that the gap between the electrodes is much narrower and also results in the alignment of the electrical field with the THz light waves, which leads to a considerably stronger antenna enhancement.

Using the new arrangement the A*STAR team were able to generate THz radiation of about 100 times the strength of that produced by conventional systems. The work suggests that these devices can be miniaturized significantly for compact yet powerful THz sources. “This approach will greatly facilitate the applications of THz technology in areas such as gas sensing, non-destructive inspection and testing, high resolution spectroscopy, product quality monitoring and bio-imaging,” says Teng.

Explore further: Terahertz imaging goes the distance

More information: Tanoto, H. et al. Greatly enhanced continuous-wave terahertz emission by nano-electrodes in a photoconductive photomixer. Nature Photonics 6, 121–126 (2012).

Related Stories

Terahertz imaging goes the distance

April 26, 2007

Terahertz (THz) radiation, or far-infrared light, is potentially very useful for security applications, as it can penetrate clothing and other materials to provide images of concealed weapons, drugs, or other objects. However, ...

Terahertz-controlling device is built

December 4, 2006

U.S. government scientists say they've built a device that can manipulate terahertz radiation, perhaps leading to new imaging and communications devices.

Checking people at airports -- with terahertz radiation

September 18, 2008

Within the last few years the number of transport checks – above all at airports – has been increased considerably. A worthwhile effort as, after all, it concerns the protection of passengers. Possibilities for new and ...

Recommended for you

Lightning, with a chance of antimatter

November 22, 2017

A storm system approaches: the sky darkens, and the low rumble of thunder echoes from the horizon. Then without warning... Flash! Crash!—lightning has struck.

How the Earth stops high-energy neutrinos in their tracks

November 22, 2017

Neutrinos are abundant subatomic particles that are famous for passing through anything and everything, only very rarely interacting with matter. About 100 trillion neutrinos pass through your body every second. Now, scientists ...

Quantum internet goes hybrid

November 22, 2017

In a recent study published in Nature, ICFO researchers led by ICREA Prof. Hugues de Riedmatten report an elementary "hybrid" quantum network link and demonstrate photonic quantum communication between two distinct quantum ...

Enhancing the quantum sensing capabilities of diamond

November 22, 2017

Researchers have discovered that dense ensembles of quantum spins can be created in diamond with high resolution using an electron microscopes, paving the way for enhanced sensors and resources for quantum technologies.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.