Re:A Visionary Project Aims for Alpha Centauri, a Star 4.37 ...
by maxander on Tuesday April 12, 2016 @06:23PM
(#11484097)
So it sounds like we'd have a layered sequence of dialectric mirrors (themselves many layers each) each reflecting a different wavelength. The first layer lasts until the laser redshifts out of that layer's efficient reflection range, then vaporizes revealing the next layer tuned to the redshifted laser. That layer lasts until the laser redshifts even further, then vaporizes to reveal the next, and so on.
Sacrificial layers may also help with heat management, I suppose.
Re:A Visionary Project Aims for Alpha Centauri, a Star 4.37 ...
by vilhelm_s on Wednesday April 13, 2016 @11:48AM
(#11489207)
Some types of lasers (e.g. free electron lasers) can be tuned to arbitrary wavelengths, so you could maybe adjust the frequency of the laser as the craft accelerates.
Re:A Visionary Project Aims for Alpha Centauri, a Star 4.37 ...
by stcredzero on Tuesday April 12, 2016 @03:29PM
(#11482786)
IIRC, Robert Forward was writing about sails using dielectric mirrors with holes in them back in the 80's.
Re:A Visionary Project Aims for Alpha Centauri, a Star 4.37 ...
by jessriedel on Tuesday April 12, 2016 @04:28PM
(#11483275)
Yea, david-given links to one of Forward's old paper elsewhere in this thread.
"Use a material with better than 99.999% reflectivity. Usually, highly reflective surfaces are dielectric mirrors, which are composed of ‘sandwiches’ of material, with each layer reflecting back a modest fraction of the total. Each layer needs to be at least a quarter of a wavelength thick. The weight can be reduced by using a monolayer with high reflectivity at the correct wavelength. Based on recent research, this could be achieved by a ‘hole-pocked’ layer, highly reflective for very specific angles where reflectivity caustics arise. (These caustics occur for wavelengths of light that are actually longer than the sheet thickness.)"
http://breakthroughinitiatives.org/index.php?controller=Foru...