Question

Powerful lasers are highly intense, diverge negligibly and are also coherent. These radiations are emitted through partially reflecting mirrors after simultaneous reflections within the lasing medium. Don't these EM radiations affect the lasing medium or reflecting mirrors?

Also, How is plasma used as a lasing medium in certain lasers?

Answer 1

Several misconceptions here

is extremely intense

Except when it isn't, there is no requirement that lasers be intense, just the ability to get intensity when you want it, and low power applications exist. Your link say things like "Low to medium power laser diodes are used in laser printers and CD/DVD players."

doesn't diverge

All lasers diverge to some extent given by their initial aperture, and the diode lasers used in laser pointers and similar applications have enough divergence to notice in a medium to large room. With typical benchtop lasers you may need a hundred meters or more to notice a significant divergence. The second paragraph of your link covers this: "Spatial coherence typically is expressed through the output being a narrow beam which is diffraction-limited".

Lasers are available in various UV bands (I've used a N2 laser at 337 nm) and there are theories about how to get lasing in the x-ray band (pumping by a nuclear explosive for one). Your link also covers this, and even has this image enter image description hereof the commercially available wavelengths that clearly shows UV lasers that you can buy off the shelf.