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0 pointsjessriedel10y ago0 comments

Yep.

"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...

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maxander10y ago

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.

vilhelm_s10y ago

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.

stcredzero10y ago

IIRC, Robert Forward was writing about sails using dielectric mirrors with holes in them back in the 80's.

jessriedelOP10y ago

Yea, david-given links to one of Forward's old paper elsewhere in this thread.

http://path-2.narod.ru/design/base_e/starwisp.pdf

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