Re: How it's done
Not for any glass bead, as it won't necessarily retroreflect (ie send the incoming light back in the same direction it came from, regardless of incident angle), unless it's been deliberately manufactured to, with a retro reflective backing to it. The reflective studs in roads ("cat's eyes" in the UK and possibly elsewhere) do this but only because they have the retroreflective material behind the glass bead. I think the glass bead only works to provide protection from the elements and being run over whilst still allowing the light in and back out.
Animal eyes that retroreflect only do so for a very narrow range of incident angles. If you've ever seen the effect for yourself, you may notice the animal's eyes shine really bright (if you're illuminating them) only when they turn to look at you.
Cameras can retroreflect over a large range of incident angles due to the way the imaging sensor reflects incident light. It's a phenomenon that had been known about for a long time, but the novel thing here is using the existing built in smartphone lidar to do it.
There's a similar effect in RF, where a horn antenna will retroreflect the incident electromagnetic wave if it's at the right frequency. Makes it very hard to build a radar that is in turn stealthy to other radars. One if the reasons to move towards phased array radars target than mechanically scanned antennas.
Biting the hand that feeds IT
