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...

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.

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.

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

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

Well, that sure is a good point.

Upon further reading, looks like you can achieve >99.9998% reflectance for a 10% wavelength band (in this case, in the infrared). [http://www.crystallinemirrors.com/wp-content/uploads/2013072...]

Still, you're right in saying that it's probably still quite a ways off.

Keep in mind that a single spaceship wouldn't take up the whole beam - for one thing, there would be a bunch of them, and for another, we simply can't focus a laser on something the size of an iPhone from even as far away as the moon. That said, it is still a massive amount of power that needs to be reflected.

I thought this also, but "[...] to keep the beam tightly focused on one probe at a time would require [...]" in the original article points in the opposite direction.

Article says it needs to be better than 99.999%

iphone innards - done

99.999% reflective mirror - done (iphone gorilla glass ;)