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*To*: T.L.G.vanderLinden@student.utwente.nl (Timothy van der Linden)*Subject*: Problems with beaming*From*: Steve VanDevender <stevev@efn.org>*Date*: Sat, 6 Apr 1996 11:37:35 -0800*Cc*: KellySt@aol.com, kgstar@most.fw.hac.com, stevev@efn.org, jim@bogie2.bio.purdue.edu, zkulpa@zmit1.ippt.gov.pl, hous0042@maroon.tc.umn.edu, rddesign@wolfenet.com, David@InterWorld.com, lparker@destin.gulfnet.com, DotarSojat@aol.com*In-Reply-To*: <199604061858.AA08809@student.utwente.nl>*References*: <199604061858.AA08809@student.utwente.nl>

Timothy van der Linden writes: > To Lee, > > >There are two problems really. First of all; there is the inverse square > >law, the intensity (and therefore the power) of radiation decreases as the > >inverse square of the distance. I have not seen anyone's calculations here > >take into account the amount of power that must be generated HERE in order > >to provide a reasonable amount of power THERE. > > Yes, but lasers keep a tight beam and thus their diametre (cross-section) > does not increase with distance and the energy-density (per surface) stays > the same. > So I don't see a problem here. Actually, practical lasers do diverge with distance. Coherency does not mean unidirectionality. For example, lasers that work by reflecting light between two mirrors produce a primary beam where an integral number of wavelengths N falls between the mirrors, and a secondary annular beam where N+1 wavelengths fall between the two mirrors, with a slight angle between the primary beam and the secondary annular beam. The angle isn't noticeable in typical lasers and laboratory distances, since it's on the order of milliradians; shining the laser over a long enough distance would show a bright spot surrounded by a ring, rather than just a spot (assuming your mirrors are that good, anyway).

**References**:**Problems with beaming***From:*T.L.G.vanderLinden@student.utwente.nl (Timothy van der Linden)

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