US developing untraceable weapons

[Steve Schear]

At 10:17 PM 10/12/2002 -0400, Tyler Durden wrote:
>Well, there was also some other details left out by that article. A "100kW 
>beam" doesn't tell you very much if you don't know the beam diameter.

It tells you the output power, from which one may estimate input power 
requirements.

>A 1310nm telecom laser can cause serious eye damage with 10mW, but that's 
>10mW into, say 38 um^2. But it ain't going to do nothing to enemy aircraft 
>located at a distance. A 100kW laser might easily have a smaller energy 
>density depending on the diameter. In addition, there's the problem of 
>focusing that thing through turbulence, but turbulence through certain 
>wavelength windows may not be a problem.

Beam spread is one of the most significant considerations in delivering 
high energy to distant targets. In general, one wants a large beam size to 
reduce divergence.

The phenomenon of diffraction influences the propagation of Gaussian light 
beams. The output of a laser is generally ''pencil-like'' in nature and has 
a very low divergence, yet is subject to diffraction that causes it to 
spread. Gaussian beam theory deals with this effect.  The Rayleigh range, Z 
sub R, is used as a criterion for determining the spreading of a 
monochromatic Gaussian light beam as it propagates in free space.

In 1987 it was discovered that were ''nondiffracting'' beam types.  The 
zeroth-order Bessel beam is one such solution and results in a beam with a 
narrow central region surrounded by a series of concentric rings.  Ideally 
this beam type exhibits no diffraction or spreading, in practice it is 
possible to obtain Bessel beams of less than 1/10 the divergence of a 
Gaussian beam of otherwise similar properties.  Bessel beams have been the 
subject of intense investigastion for a broad range of optical applications.

http://www.st-and.ac.uk/~atomtrap/papers/AJPBessel.pdf
http://www.st-and.ac.uk/~atomtrap/Research/IBB.htm