Engineers and applied physicists from Harvard University have demonstrated the first room-temperature electrically-pumped semiconductor source of coherent Terahertz (THz) radiation, also known as T-rays. The breakthrough in laser technology, based upon commercially available nanotechnology, has the potential to become a standard Terahertz source to support applications ranging from security screening to chemical sensing.
Spearheaded by research associate Mikhail Belkin and Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, both of Harvard's School of Engineering and Applied Sciences (SEAS), the findings will be published in the May 19 issue of Applied Physics Letters. The researchers have also filed for U.S. patents covering the novel device.
Using lasers in the Terahertz spectral range, which covers wavelengths from 30 to 300å, has long presented a major hurdle to engineers. In particular, making electrically pumped room-temperature and thermoelectrically-cooled Terahertz semiconductor lasers has been a major challenge. These devices require cryogenic cooling, greatly limiting their use in everyday applications.
"By contrast, our device emits T-rays with several hundreds of nanowatts of power at room temperature and microwatts of power at temperatures easily achievable with commercially available thermoelectric coolers," says Belkin. "Further, there is the potential of increasing the terahertz output power to milliwatt levels by optimizing the semiconductor nanostructure of the active region and by improving the extraction efficiency of the terahertz radiation."
To achieve the breakthrough and overcome the temperature limitations of current laser designs, the researchers engineered a room temperature mid-infrared Quantum Cascade Laser (QCL) that emits light at two frequencies simultaneously. The generation of Terahertz radiation occurs via the process of difference-frequency generation inside the laser material at room temperature at a frequency of 5 THz (equal to the difference of the two mid-infrared QCL frequencies).
Mid-infrared QCLs were invented and demonstrated by Capasso and his team at Bell Labs in 1994. The compact millimeter length semiconductor lasers operate routinely at room temperature with high optical powers and are increasingly used in the commercial sector for wide range of applications in chemical sensing and trace gas analysis. The devices, made by stacking ultra-thin atomic layers of semiconductor materials on top of each other, are variable and tunable, allowing an engineer to adjust the energy levels in the structure to create artificial laser medium.
"Terahertz imaging and sensing is a very promising but relatively new technology that requires compact, portable and tunable sources to achieve widespread penetration. Our devices are an important first step in this direction," said Capasso. "We believe our THz source has great development potential because the nanoscale material used was grown by Molecular Beam Epitaxy, a commercial and widely used thin film growth technique which 'spray paints' atoms on a surface one layer at a time."
The ability of Terahertz rays to penetrate efficiently through paper, clothing, cardboard, plastic and many other materials makes them ideal for use in many applications. For example, a device emitting T-rays could be used to image concealed weapons, detect chemical and biological agents through sealed packages, see tumors without causing any harmful side effects, and spot defects within materials such as cracks in the Space Shuttle's foam insulation.
Michael Patrick Rutter | EurekAlert!
Tune your radio: galaxies sing while forming stars
21.02.2017 | Max-Planck-Institut für Radioastronomie
Breakthrough with a chain of gold atoms
17.02.2017 | Universität Konstanz
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
21.02.2017 | Earth Sciences
21.02.2017 | Medical Engineering
21.02.2017 | Trade Fair News