[edwin hubble]

See where terahertz radiation fits into the continuum of the electromagetic spectrum:

The electromagnetic spectrum in order (short to longer wavelength): gamma ray, x-ray, Ultra-violet, visible, infra-red, terahertz, microwave, radio.

The terahertz region has been (for 100 years) a kind of no-man's-land, lying between the infra-red light and the microwave radio.

Terahertz radiation:
* interacts with (and is partially absorbed by) some matter,
* is largely absorbed by some matter,
* passes through some matter without being altered, and
* reflects from other matter.

So it can tell a Lot about the type of matter it is striking.

It is much shorter in wavelength (higher resolution) than microwave.

We have only begun to study this last area of the spectrum.

[edwin hubble]

But..

Terahertz technology is not conventional infra-red.
It doesn't function with the same optical devices.