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Message: <blockquote data-quote="Agemegos" data-source="post: 2788795" data-attributes="member: 18377">You are forgetting about diffraction. The tightest that any beam can be held in principle is a number of radians approximately equal to the wavelength divided by the beam width. In any sort of laser small-arm you are going to keep the beam narrow to give a high intensity at manageable power consumption, especially considering that you want to minimise attentuation by thermal blooming. The best way to do that is to use a very narrow beam, else the effect takes too long and vampirises too much of your pulse energy. I would be aiming for a sub-millimetre beam width, but lets consider a 100mm-wide flashlight-like beam to produce a generous limit.Now various considerations suggest that laser smallarm aren't going to use a wavelength much shorter than about 100nm--you don't want to try a wavelength at which air is opaque, for a start. So very generously, beam width might be a million times wavelength. So at one kilometre the beam can be brought to a focus one millimetre across: it is effectively parallel. But at 1,000 km the beam is at least one metre across, and its intensity is only 1% of what it was at the muzzle. No laser smallarm is likely to be dangerous at a range of 1,000 km. That's a long way on a battlefield (620 miles), but nothing out in space.Each further factor of ten in distance increases the beam width by a factor of ten and reduces beam intensity by a factor of one hundred.</blockquote>

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