The terahertz gap: into the dead zone (2007)

[1] https://opg.optica.org/abstract.cfm?uri=OFC-2022-M3C.6 [2] https://en.wikipedia.org/wiki/6G_(network)

While the wavelength of THz is larger than IR, and hence leads to a worse spatial resolution due to diffraction. This comment is about the scattering of light through a medium, which acts as a low pass filter leading to loss of higher spatial frequencies and therefore lower spatial resolution.

> millimetre wave astronomy is a big topic of the last decade or two. How does the THz technology described here link to what's used in mm wave detection?

They are effecitevely the same band (1mm ~ 0.3THz). The difference between astronomy and other applications is photon flux. Distant astronomical objects are faint, therefore detection methods only need to detect a small number of photons/s. One popular detector is cryogenic bolometers, which measure a temperature increase due to absorbed energy from a THz photon. These work well in low-flux applications.

According to this claim, many common materials would diffuse the infrared light so that the image would look like looking to something through translucent glass or through fog, which would diminish the resolution.

I assume that this refers to imaging through visually opaque materials, i.e. through clothes, like for airport security, not to looking through the air with an infrared camera.

Just like you might say that a lawnmower is compliance tested against electrical faults before sale and is thus safe to use, despite having some sharp rotating blades on the bottom that could ruin your day pretty quickly if you put your head in it and turned it on.

The way EM radiation works is that it's classified as ionising if it's sufficiently energetic and penetrative (read: high frequency/short wavelength) to enter human tissue and detach electrons in the atomic structures that make up that tissue.

The danger that ionising radiation presents is that detaching electrons in DNA can cause carcinogenic mutation i.e. cause cancer.

Radiation in high-frequency ultraviolet and above in the EM spectrum is considered ionising, and everything from low-freq UV below is considered non-ionising. This is because the energy carried by EM waves of lower-than-UV frequency is not sufficient to ionise atoms in human tissue.

I don't know the exact numbers on that, but I do know that the lowest threshold for ionising any atom is 3.9eV (low f UV) to ionise a caesium atom — and obviously we aren't made of caesium.

And this is backed up pretty well by the fact that if visible light were dangerously ionising EM radiation, life would not exist as we know it, and even if it made it this far, we'd all have a lot of cancer.

And since visible light is ostensibly higher frequency/higher energy than this "terahertz radiation" (presumably a buzzword for high freq microwave/infrared?) we can safely say that it won't hurt us in the way that a thousand chest X-rays might.

Now it's true that you can burn your food in the microwave and you can blind yourself with a laser, but this isn't because you ionised your chicken beyond core cooked temperature, it's because you subjected it to intense microwave radiation which excites the atoms.

Sufficiently intense visible light will burn your skin, but it won't mutate your skin. You get skin cancer from excessive exposure to ultraviolet, not from light.

Cellphones, wifi and 4G/5G have all been used by those who profit from scaremongering, but if you think about it, if any of it were true, there would have to be some new science to describe the mechanism by which they cause harm.

Another convention is sub-mm, given the wavelength is just that, being on the order of microns.