Technology Inches On: Ship Lasers

[SSWarlock]

I've always wondered how ship lasers can reach so far without dispersing because of the inverse square law and I've never liked the handwaved gravitic lensing/compression/whatever of TNE. Being a fan of cool science research, the following news post made me say "hmm"; scientists may be working on a real world solution right now and not even realize it.

http://www.sciencedaily.com/releases/2015/09/150910141238.htm

If "molecules" of light really can be produced, then perhaps a "self-cohering" beam of them can be created as well.

 

[Reynard]

We hit mirrors on the moon at 384,400 Km to bounce it back to a receiver. Doesn't take light long to cover both distances to keep it accurate, approximately 3 seconds both ways. The moon is seven times the Distant range so even a Particle beam at maximum Distant is reaching a target in 0.17 seconds. I don't believe there's much dispersal in combat.

 

[Anonymous]

Lasers and the inverse square law are slightly complex. They obey it, but the divergence is delayed for some distance due to the focussing of the laser. A laser is a gaussian beam which has something called a rayleigh distance up until which the beam is effectively parallel and not subject to the inverse square law.

It seems you looking for information on how a laser beam is generated and ways to extend the rayleigh distance of the beam, but in real life or in Traveller?

edit: I should add that in real life, the distance is proportional to the width of the beam, and inversely proportional to its wavelength. Up until that point, no inverse square law applies.

 

[simonh]

We hit mirrors on the moon at 384,400 Km to bounce it back to a receiver. Doesn't take light long to cover both distances to keep it accurate, approximately 3 seconds both ways. The moon is seven times the Distant range so even a Particle beam at maximum Distant is reaching a target in 0.17 seconds. I don't believe there's much dispersal in combat.

According to this article about the experiment the beam is 7 km across when it reaches the moon, and the part of it that's reflected back by the retroreflectors (which in the pictures look less than a meter across to me) is 20 km across when it gets back to Earth. I suppose the retroreflectors mess up the beam coherence, hence the greater divergence on the return journey.

Anyway, this suggests that you'd expect roughly 1km beam widths at Distant range. Sure you might be able to optimize that down a bit, but that's a heck of a lot of optimizing to get a beam width useful in combat.

Simon Hibbs