Lin Liu

Light in a thin film of lithium niobate can be made to change color — for instance, turning an invisible infrared beam into green. To do that, the crystal needs to be 'marked': in some places its polarity points up, in others down. Previously, this marking was done by applying a voltage and watching the domain growth in real time. The slightest delay, and the pattern smears.

Light from an ordinary bulb seems utterly chaotic: its waves oscillate out of sync, like a crowd where everyone walks in their own direction. Such light is called incoherent. For a long time, it was believed that elegant topological structures (knots, rings, links) could only be created in coherent laser light, where all waves march in step.