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T-ray Pulses Produced by QCL

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PARIS, May 2, 2011 — For the first time, terahertz rays, or T-ray pulses, have been made to emit separate "packets" of terahertz radiation, rather than one continuous beam, from a quantum cascade laser. The work could open up new ways for the T-rays to image natural and synthetic materials.

Researchers from Denis Diderot University in Paris, the French National Center for Scientific Research, and the University of Leeds in the UK published their work online in Nature Photonics.

The term "T-rays" describes a band of radiation in the electromagnetic spectrum that falls between radio waves and visible light. T-rays can be used to detect impurities in chemical and biological materials, generating characteristic "spectral fingerprints" that are used to identify various substances.

Harnessing the power of a quantum cascade laser that is almost 10,000 times more powerful than previous versions, researchers created a T-ray pulse train, an advance that confirms that the technique can be used for probing materials. (Image: iStockphoto)

Researchers have recently become interested in a technique known as terahertz time-domain spectroscopy, a particularly sensitive way of probing materials using pulses of T-rays. Until now, these pulses have been made using laser sources that generate very little power (around one-millionth of a watt).

In this latest work, Stefano Barbieri and colleagues from Paris, together with Edmund Linfield and Giles Davies from the University of Leeds' School of Electronic and Electrical Engineering, harnessed the power of a quantum cascade laser (almost 10,000 times more powerful than previous versions) to create a train of T-ray pulses. They also devised a way of detecting the full pulse train, confirming that the technique could be used for probing materials.

“The potential for T-rays to provide new imaging and spectroscopy techniques for a range of applications such as chemical and atmospheric sensing or medical imaging is immense,” Linfield said. “This breakthrough provides a significant advance in the underpinning technology.”

The research was supported by the Délégation Générale pour l'Armement, the National Agency for Research, the UK Engineering and Physical Sciences Research Council, and European Research Council programs NOTES and TOSCA (Optoelectronics — from the Science of Cascades to Applications).

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May 2011
electromagnetic spectrum
The total range of wavelengths, extending from the shortest to the longest wavelength or conversely, that can be generated physically. This range of electromagnetic wavelengths extends practically from zero to infinity and includes the visible portion of the spectrum known as light.
Délégation Générale pour lArmementDenis Diderot Universityelectromagnetic spectrumEuropeEuropean Research CouncilFranceimagingParisquantum cascade lasersResearch & Technologyspectral fingerprintsStefano BarbieriT-ray pulsesterahertz time-domain spectroscopythe French National Center for Scientific Researchthe National Agency for Researchthe UK Engineering and Physical Sciences Research Councilthe University of LeedsTOSCAUKlasers

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