Mike Beversluis

Monday, December 21, 2009

Pew Pew

The Physics of Space Battles

Pedantic note:  He says "In space, laser light will travel almost forever without dissipating from diffraction," which is not true at all.  Diffraction works just fine in a vacuum and a diffraction-limited beam (ie, one that is not limited by any engineering compromises in the optics, but only limited by the fundamental effect of light's wave-like propagation) will spread by an angle roughly equal to the beam diameter divided by the wavelength.  A green (lambda=0.5um) 5 cm diameter diffraction limited laser beam will have an angular spread of about 1/10000 radians, so at 10km it will be about a meter wide.  Ish.  Whether the beam is traveling in vacuum or air or glass doesn't really affect diffraction at all.

There would be less scattering and absorption by random particles and clouds and less refraction by turbulence cells and inversion-layers, etc, ie, things that really do bother current atmospheric propagation of high-intensity laser beams (and stars, that's why they twinkle).  That might be what he meant, but that's not what he said.

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