Maximizing Laser Focus: Understanding Divergence and Distance Limitations

[easyrider]

I know that lasers will always have divergence due to diffraction. With that said, they don't diverge until after the point of focus, correct? Is there a limit to how far a laser can be focused?

 

[Andy Resnick]

Gaussian beams are fairly easy to describe in terms of the beam waist and divergence angle- one important derived quantity is the Rayleigh length:

http://en.wikipedia.org/wiki/Rayleigh_length

 

[easyrider]

Thanks for your reply. If one has a big enough aperture and the right optics, you could focus it out to 1 or 2 light-seconds couldn't you? Is there a limit to how far off a laser can be focused?

 

[Andy Resnick]

There has been some work on deep-space communication systems (NASA's LCRD and LADEE experiments), and AFAIK there's a multi-satellite design by ESA that uses lasers to remain in a fixed configuration for gravitational wave detection (LISA)- not sure what stage in development they are, tho.

Note that atmospheric turbulence/scattering makes long distance laser systems (Boeing's airborne laser system, for example) hugely complicated- the THEL (Nautilus) system was shelved.

 

[easyrider]

There has been some work on deep-space communication systems (NASA's LCRD and LADEE experiments), and AFAIK there's a multi-satellite design by ESA that uses lasers to remain in a fixed configuration for gravitational wave detection (LISA)- not sure what stage in development they are, tho.

Note that atmospheric turbulence/scattering makes long distance laser systems (Boeing's airborne laser system, for example) hugely complicated- the THEL (Nautilus) system was shelved.

Hm, please elaborate. What do you mean by uses lasers to remain in a fixed configuration? Dyou have a link/site with more info? Also, yes I am aware of atmospheric effects on the beam, I meant strictly in a vacuum.

 

[Andy Resnick]

ESA's LISA mission: http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=35617

NASA's LCRD mission: http://www.nasa.gov/mission_pages/tdm/lcrd/index.html