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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?

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In my capacity as a plain old user (i.e. without my moderator hat on) I do not feel that linking to a wikipedia article that you evidently haven't even read in its entirety constitutes doing your homework. You have at least three misconceptions in here and they are all covered in the wikipedia article. –  dmckee Sep 8 '12 at 15:48
Of course there are other forms of LASER, and X-ray lasers are described there. This question can't possibly be useful to anyone else. –  Ron Maimon Sep 8 '12 at 15:59
The problem is that now it's a different question! Yes, plasma lasers exist, these are the X-ray lasers, and there was even talk by Teller of lasing the plasma in an atomic detonation. This is known and you should review the literature and ask a focused question. –  Ron Maimon Sep 9 '12 at 3:35
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closed as not a real question by Ron Maimon, Waffle's Crazy Peanut, dmckee Sep 10 '12 at 14:49

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

3 Answers

There are excimer lasers that emit UV and X-ray lasers that emit X-rays. There has been discussion of lasers based on nuclear transitions, though opinion is divided about whether these could ever be made to work.

Conventional optical lasers use mirrors at either end of the laser cavity to get the multiple passes needed for lasing. Mirrors stop reflecting EM waves above hard UV energies so the design of high frequency lasers gets challenging, but it can be done.

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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 $\mathrm{N}_2$ 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.

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Removed the unnecessary negative vote to a perfectly reasonable question. +1

  • Do the reflecting elements have problems when the beam intensity is very high?

It is possible, but the lasers have to be very intense for that to happen (maybe MW/cm^2 or more). Depending on the wavelength of light being emitted, the reflecting elements are coated with metal (Al, Au for example) or with a dielectric. All reflecting elements in a stock high power laser should be designed to handle large power. The problem arises when the end user puts in the wrong kind of optical element, and this problem usually manifests as beam distortion that could misalign the laser (if it is part of the lasing cavity) and decrease the output power.

The most common problem however, is dust. Even with a "low" power 500mW IR laser, dust settling on the optical elements get scorched and interfere with the generation of light. Anybody who has worked with a Ti:Saph laser or an Argon ion laser will tell you that if your output power drops, clean the cavity mirrors before checking for alignment issues.

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