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Problems with beaming
- To: T.L.G.vanderLinden@student.utwente.nl, kgstar@most.fw.hac.com, stevev@efn.org, jim@bogie2.bio.purdue.edu, KellySt@aol.com, zkulpa@zmit1.ippt.gov.pl, hous0042@maroon.tc.umn.edu, rddesign@wolfenet.com, David@interworld.com, lparker@destin.gulfnet.com
- Subject: Problems with beaming
- From: DotarSojat@aol.com
- Date: Sun, 7 Apr 1996 16:22:56 -0400
A laser beam with wavelength lambda that has been formed by a
primary objective mirror with an aperture diameter D will di-
verge in the far field (never mind, that's where you want to
work) due to diffraction. I don't have the explicit relations
at home, but I believe that the angular width of a "diffraction-
limited" beam at half maximum is the same as that used in the
Rayleigh criterion: 1.22 lambda/D.
This width is further broadened due to (1) thermal effects in
the lasing medium, by a factor called "beam quality" that is in
the range 1.1-1.3, depending on the type of laser, and (2) beam-
pointing instability called "jitter," usually about one-third
the diffraction-limited beam divergence, that enters in a root-
sum-squares way. The overall angular beam width of a contempo-
rary laser "weapon" is of the order of a microradian. A factor
of ten reduction (narrowing) in beam width by the time an inter-
stellar mission would be undertaken would not be unreasonable to
expect.
Regards, Rex