"Magic" Teraherz beams to identify the Terrists.. Amazing pictures

Terahertz (1,000 MHz) radiation lies between the microwave and far-infrared regions of the electromagnetic spectrum, at wavelengths from about 1 to 0.03 mm.

It passes through most materials, including humans but not , therefore it could be used to detect concealed weapons or explosive chemicals.

Whilst devices, known as QCL's have been able to emit light at such wavelengths for some time it required the semiconductor crystals to be cooled to less than 200 Kelvin which ssverely restricted their use.

Now Federico Capasso of the Harvard School of Engineering and Applied Sciences and colleagues from Texas A&M University and ETH Zurich have demonstrated a system that emits terahertz radiation with several-hundred nanowatts of power at room temperature.

This “difference-frequency generation” (DFG) system exploits a characteristic of materials they have developed, so that when illuminated by two frequencies of light, the electrons re-emit photons at both of the individual frequencies as well as the frequency difference. When the two frequencies are in the mid-infrared, the QCL can produce a difference frequency of 5 THz.

Previous systems using this technique required powerful pump lasers and large non-linear crystals to generate the required frequency difference. The new device is electrically pumped. and one small semiconductor crystal a few millimetres in size affords the prospect of portable, small, low power systems.

Such compact semiconductor light sources would have applications in studies of pharmaceutical products, drug detection and determination of disease in skin tissue.... but detecting gun toting terrists is more exciting and assurance of a steady stream of income for the lab.

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