[Physics] Electromagnetic radiation lenses

Question

This will probably be a very basic question, but looking for a simple answers.

What I know

• the visible light is a form of electromagnetic radiation with a defined wavelength.
• the full spectrum contains radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.

For the visible light exists many types of lenses and/or mirrors – where the refraction changing the direction of waves – e.g. focusing lenses, made of transparent material like glass.

Do such lenses exist for other types of electromagnetic radiation? E.g. Are there lenses for radio waves or for X-rays? What materials are they made of ? What about the mirrors (e.g. gamma ray mirror) ?

If such mirrors/lenses do not exist, then why not?

Can someone point me to some basic articles tolearn about this?

Answer 1

If you're looking at radio waves then the mirror will have to be made of thicker metal, because as you increase the wavelength you also have to increase the thickness of the metal to get the same reflectivity. That's actually how satellite dishes work. They're basically a big curved mirror that concentrates all of the microwaves coming down from the satellite. They're often full of holes to keep the weight down, and this doesn't matter because the wavelength of the waves is larger than the holes. This is the same principle as seeing a light on in your microwave. You can see the light escaping through the door but the microwaves aren't escaping because they're too long. Once you get beyond visible light into the shorter wavelengths; ultraviolet light is easy to make mirrors for, but x-rays are very difficult. And so making x-ray telescopes is very difficult. Sometimes they do it by using a bag of gas to act like a lens rather than mirrors or by using a metal mirror but at a very grazing angle which makes the mirror very large. Mobile phone waves are at the microwave end of radio waves, and a sheet of aluminium would work nicely as a mirror for those.

Source : the naked scientists

One can see that for making lenses, materials of different refractive indices can be used based on required convergence, divervence and dimensions can be compared to those of the above described mirrors, Although there may a problem that making enormous lenses for radio waves require materials/machinery that we may not have at the moment, mirror though as you see are the big satellite dishes that we have seen many times.