Room Temperature Semiconductor of T-Rays

Fallen Andy noted a Physorg story that says "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." "What did you do at the office today, honey?" "Oh, I just demonstrated the first room-temperature electrically-pumped semiconductor source of coherent Terahertz radiation. How was your day, dear?"

Re:What can T-Rays do?

[mckinnsb]

From reading the article, my layman's-"I'm no physicist"'s take on T-Rays:

1) They can penetrate through clothing/plastic/flesh, and most of the materials mentioned seem to be organic in nature. This gives them "X-ray"-like properties.
2) They were able to make T-Rays before in laboratories, but now they can make them more cheaply, with less power, in human-friendly settings.
3) T-Rays give off less radiation than X-rays, due to the much larger wavelength.

Quick Conclusion: We now have the potential to create an X-ray like device that could be deployed in airports and other travel hubs that could be used to monitor the public without harming the public through this observation. More benignly, they could also be used in hospitals for "persistent monitoring" of patients with tumors or internal bleeding, because they seem to have lower power requirements and risks of side-effects.

T-rays for security, medicine

[Speare]

The blurb has a lot of jargon but no reference as to what uses T-rays are likely to be put. T-rays applications [sciencedaily.com] They're likely to help with certain cancer scans within the body, but these are also the basis for new "scan 'em naked at fifty paces" airport security cameras. I'm not sure I'm too excited about advancement in this technology just at the moment. Yeah, yeah, scanners don't scan people, overzealous control-freak post-democratic regimes scan people. But you get my drift.

Very nice. Here's the real source

[Animats]

First, here's the real paper. [harvard.edu] Actually, this is the previous paper, where they got operation at 177K, but not quite room temperature. (Don't link to Physorg; they just collect press releases, add ads, and delete the citations.)

Terahertz waves are interesting. At one time, that was an inaccessible portion of the spectrum, above radio but below infrared. Now it's understood that it's a region in which both RF and optical techniques can work. At that frequency, propagation is line of sight, although diffuse systems, as with diffuse IR, are possible. Applications are still a ways off, but there's probably something useful to do with this stuff.

Incidentally, "radio", by international agreement, ends at 3THz. Beyond that, it's "light" for regulatory purposes. In the US, FCC regulations (for RF) end at 3THz, and DHS regulations (as for lasers) begin.

T-rays have imaging and security applications

[Reality Master 201]

T-ray imaging systems are what are being proposed to scan people in airports and other secure places; you can get images under a person's clothing, so you can actually see what they might have concealed.

Check out the wikipedia page: http://en.wikipedia.org/wiki/Terahertz_radiation [wikipedia.org]

Re:What we REALLY need

[jd]

With the evolution of very low power, high resolution MRI systems, that's entirely possible. Highly sensitive sensors are generally cheaper than 2.5T (and would be a LOT cheaper than 9.2T) magnets and accompanying shielding. On the other hand, any new field is going to take time to move from early uses to mainstream, and getting sensors to the limits of existing MRI technology is going to take a whole lot longer. (It's one thing to demonstrate basic imaging - which is quite good enough for many purposes. It's quite another to get to the point of imaging down to the level of individual neurons. I'm guessing the 12T magnets used in animal experiments provide far more detail yet.)

No unit goof

[supergumby]

The units and quantities used in the article are correct. Two lasers, with wavelength in the range of 3 to 30 nanometers, shine into a magic box. Out of the magic box comes light with a wavelength which is the difference of the two input lasers. The magic box is a material with a nonlinear response to electromagnetic waves, such as gallium arsenide.

Re:What can T-Rays do?

[kestasjk]

In fact the spectrum from microwaves to visible light is on the scale of THz, though specifically they refer to the portion between microwave and infra-red. They're really nothing like X-rays which are way over on the other side of visible light.

So on the one hand you have visible light and infra-red which ca\n't go through anything, on the other side you have microwaves which can go a short way through a soup or frozen chicken, and in the middle you have "T-rays" which can go through clothing but not weaponry and body parts.

Not sure exactly why IR and microwaves have been so easy to generate while "T-rays" are so difficult, and I wish they'd come up with a better name than "T-ray" because technically visible light and infra-red are THz too.

Even Higher Frequencies Possible?

[Doc Ruby]

This THz frequency laser was made by building cheap and efficient IR lasers differing from each other by only a tiny wavelength difference, then using them to excite the active lasing material at their "beat frequency". That technique might be usable to generate ever-higher frequency lasers.

For example, what about using two pairs of IR lasers, each pair resonating at a slightly different beat frequency? In fact a single "reference" IR laser could be split into two sources, with two different other sources each supplying their different frequencies into a THz laser of slightly different frequency. Then use those THz sources into an semiconductor active region which resonates at the beat frequency between the THz sources.

That higher frequency result could be used as one of yet another pair, generating an even higher beat frequency. And since these steps up are made from thin film deposition, they could have such a hierarchical structure all contained in a very tiny device. Perhaps in a device at a scale that offers extremely high frequency lasers, manufactured and operating cheaply, without extra HW to maintain a useful beam.

Perhaps a beam that could offer networks petabyte datarates. And perhaps, if the optical resonance junctions can be modulated by other photons, actual logic executing quickly, at low power.

Re:What can T-Rays do?

[dlenmn]

3) T-Rays give off less radiation than X-rays, due to the much larger wavelength.

It's not that they give of less radiation, it's that the radiation is non-ionizing (meaning that no photon has enough power to knock a electron free from its atoms -- that's what allows x-rays and UV to do damage). Because of how quantum mechanics works, you can blast away with as many of these photons as you like (aka, as much radiation and power as you want) and it will still be non-ionizing. It's cool stuff.

Re:zzzz

[dietlein]

1. Yes, also their skin.

No, not their skin. Kindt & Schmuttenmaer (1996). 1 cm of water attenuates frequencies above 100 GHz by several hundred dB.

3. Yes and no. They're better than X-rays for some diagnostics, but, as always, more knowledge = less peace.

X-rays and terahertz radiation are not really competitors in the medical field, due to the fact that terahertz radiation is attenuated greatly by water, and we're mostly water. You can detect some skin conditions with it, but only those in the first 1-3 mm of tissue. These are also visible to the naked eye, typically.

Now, you can look through bandages to see if a wound is healed, yes. That could be useful, but we also like changing bandages too, so it's debatable.

Re:No unit goof

[vsny]

The units are *not* correct. The article is referring to THz wavelenghts in general (30-300um's) not the "two lasers". 3-30nm would be X-rays and GaAs is not creating X-rays. In fact there is not two lasers at all, that is not how a QCL works. The blurb is not correct. You need frequency mixing to actually measure THz waves, but you don't use frequency mixing to get THz lasing in GaAs QCLs.