Reporting this month in Physical Review Letters, Grzegorczyk and colleagues at the Swiss Federal Institute of Technology in Lausanne say that they’ve used lasers to arrange about 150 beads that are 3 microns in diameter to produce a flat, reflective surface. In the experiment, the beads are contained in a water-filled glass cell. A laser beam shines under the beads, causing them to align themselves into a flat surface. To show that the surface was indeed a mirror, the researchers used it to reflect an image of the number eight made by shining light through a transparent ruler. They also calculated that a reflective surface made by shaping a flock of tiny particles into a parabola could focus an image just as a telescope mirror does.
This sounds pretty cool. I can’t access the paper at the moment, but if the viewing wavelength is large enough, any roughness of the assembly won’t matter — it will “look” smooth to longer wavelengths.