"Coherent Terahertz Generation: New Light for Nanostructures and Bio-Imaging"
By Karl Unterrainer
Since scientists realized that radio waves and light are the same phenomenon electromagnetic radiation, at different frequencies - they have naturally been
interested in the area where one shades into the other. That is "the terahertz gap". To
radio engineers it's the "sub-millimeter band", and from an optics point of view it's the
"far infrared".
The Universe doesn't have a gap: it is full of natural radiation in this range. But until
very recently there were no readily controllable sources and detection was difficult.
Show scientists a gap and they will want to peer into it, expecting interesting
discoveries.
There are practical reasons, too, for interest in this part of the electromagnetic
spectrum. The applications include systems for seeing through fog, assaying DNA,
building extremely fast local area networks of computers, seeing the extent of skin
tumors, quality control in both microelectronics and drug factories, and detecting
explosives and biological warfare agents.
And, of course, these applications include "T-ray specs". Clothes are transparent to
terahertz radiation, which is handy if you want to develop the ultimate airport security
scanner. And THz is “safe” non-ionizing radiation making it very attractive for medical
imaging.
Nanostructures have fascinating new functionalities; among them are THz optical
transitions. These quantized transitions help to provide sources and allow to merge
electronics with optics e.g. by fully control over the phase of THz light.