My university education was as a chemist, a while ago I admit. We didn’t think about the wavelength or frequency of electromagnetic radiation in the infrared, tending to use the standard units for chemists of wavenumbers (cm-1) .
In the VUV though we swapped to Electron Volts, but did use wavelength for the visible spectrum.
Nowadays I’ve converted my mind to use wavelength across the spectrum, only to find that frequency (Terahertz) is being used for the far infrared and millimetric waves.
I’ve just spent a fair bit of time answering an enquiry from Japan for metal mirrors to work with “Terahertz”, which to me means 100um – 300um wavelength. I should have checked, as I now find out its 20THz, or as I now think of it 15um wavelength. Actually our Gold coated Copper mirrors do work well in the region of 100 – 200um, or should I say the 1.5 – 3 THz spectrum, maybe longer.
This is a nice conversion tool at a US University to convert frequency, wavelength & energy