2 ms·

This could have applications in free space quantum encryption links. Signals sent in quantum communications must be at the level of single photons to ensure se

by beloch 12y ago

This could have applications in free space quantum encryption links. Signals sent in quantum communications must be at the level of single photons to ensure security. Traditionally, high repetition rates are used to overcome loss. i.e. If you have a 1 in a million chance of getting a single photon through, then trying a million times a second lets you get one photon through per second, on average. Increasing the transmission of a long free-space link could increase the maximum distance at which the link will be usable. This may be especially useful for satellite-to-ground links in less than perfect atmospheric conditions. Very cool research!

femto 12y ago
It would have limited application in satellite-to-ground links, as the photons would soon be outside the atmosphere. It is a neat idea though.
- beloch 12y ago
  Loss happens in atmosphere, not vacuum. If it increases the overall transmission the link, what does it matter if the waveguide doesn't go the full distance?
  - femto 12y ago
    I agree that it will help, to the extent that it counters diffraction of the beam whilst is in the atmosphere, hence it having "limited" application rather than no application. Diffraction still happens in a vacuum. The beam spreads, so photons are lost by not falling on the detector. The waveguide effect would counteract scattering to some degree. Even then, wouldn't scattering emit photons in random directions, meaning that the majority of scattered photons would be moving at too great an angle to the high/low density boundary to be refracted back into the beam?
- ars 12y ago
  Outside the atmosphere there is no scattering so the laser will stay as focused as it was at the start
atondwal 12y ago
> This may be especially useful for satellite-to-ground links in less than perfect atmospheric conditions. Seems to me that the ionosphere would get in the way of this kind of technique. This relys on creating a plasma in air with controlled properties to function as a waveguide, so I imagine that having a high-energy space plasma in the way would make that sort of thing very difficult.

by beloch 12y ago

femto 12y ago

It would have limited application in satellite-to-ground links, as the photons would soon be outside the atmosphere. It is a neat idea though.

beloch 12y ago
Loss happens in atmosphere, not vacuum. If it increases the overall transmission the link, what does it matter if the waveguide doesn't go the full distance?
- femto 12y ago
  I agree that it will help, to the extent that it counters diffraction of the beam whilst is in the atmosphere, hence it having "limited" application rather than no application. Diffraction still happens in a vacuum. The beam spreads, so photons are lost by not falling on the detector. The waveguide effect would counteract scattering to some degree. Even then, wouldn't scattering emit photons in random directions, meaning that the majority of scattered photons would be moving at too great an angle to the high/low density boundary to be refracted back into the beam?
ars 12y ago
Outside the atmosphere there is no scattering so the laser will stay as focused as it was at the start

atondwal 12y ago

> This may be especially useful for satellite-to-ground links in less than perfect atmospheric conditions. Seems to me that the ionosphere would get in the way of this kind of technique. This relys on creating a plasma in air with controlled properties to function as a waveguide, so I imagine that having a high-energy space plasma in the way would make that sort of thing very difficult.