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## Is There a Limit To a Laser's Energy?135

StartsWithABang (3485481) writes "For normal matter — things like protons, neutrons and electrons — there's a fundamental limit to the number of particles you can fit into a given region of space thanks to the Pauli exclusion principle. But photons aren't subject to that limit; in theory, you could cram an infinite number of them into the same exact state. In principle, then, couldn't you create a laser (or lasing cavity) with an infinite amount of energy inside? Perhaps, but there are some big challenges to be overcome!"
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## Is There a Limit To a Laser's Energy?

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• #### Re:You keep using that word (Score:4, Insightful)

on Sunday May 04, 2014 @09:08AM (#46912643)
We can outright throw it out, as there isn't an infinite amount of energy in the visible universe.
• #### Re:You keep using that word (Score:2, Insightful)

by Anonymous Coward on Sunday May 04, 2014 @10:58AM (#46913109)

No, it doesn't. In maths, we use the phrase, "finite but unbounded". This describes the natural numbers, for example: each specific integer is strictly finite, but there's no finite upper limit.

• #### That's a limit on energy DENSITY (Score:4, Insightful)

on Sunday May 04, 2014 @11:14AM (#46913215) Journal

Eventually the laser energy will create a black hole, provided some other exotic effect doesn't occur first.

That's a limit on energy density, not total energy in the laser. In principle you could use a very WIDE laser opterating below the black-hole thrshold and focus the beam externally (which, if it's powerful enough, it might do eventually, by self-gravitation, after leaving the cavity, even if the cavity geometry made it emit a colimated, rather than a converging, beam.) Thus, making a kugelblitz with a (very wide) laser might be theoretically possible (if "some other exotic effect" didn't make the required laser cavity to wide to be physically realizable).

I'd imagine "Some other exotic effects" might include the electric field component of the coherent light becoming strong enough to polarize the vacuum and create particle-antiparticle pairs from multiple photons, dissipating their energy, somewhere WAY below the threshold of gravitic-collapse effects. So you'd need a REALLY WIDE laser and REALLY GOOD optics to make your external-to-the-laser black hole.

Of course the question, being phrased in terms of Bose-Einstein vs. Fermi-Dirac statistics and "infinite" energy was really about energy density in the cavity - just poorly phrased. So you answered the question that was REALLY being asked.

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