In the ocean, sometimes a huge solitary wave appears out of nowhere and then vanishes. Such rogue waves are rare but dangerous. Similar rare and intense spikes occur in other systems, from financial markets to lasers. The problem is that they are hard to predict, let alone trigger on demand.

In the new work, physicists took a semiconductor laser — a tiny light source found in DVD players and fiber-optic lines. Inside the laser, light oscillates in two directions, like two strings that can sound separately or together. The scientists placed a mirror outside the laser, and between the laser and the mirror, a small plate that rotates the direction of light oscillation. By turning this plate, they made the two “strings” exchange energy so that one of them occasionally fired off a very bright pulse. That is a rogue wave in miniature.

By rotating the plate to different angles, one can change how often such spikes occur, how tall they are, and whether they cluster together. This is the first time rogue waves in a laser have not just been observed but precisely tuned, like adjusting the volume and tone on a radio.

Such a controllable laser could become a tool for studying rare catastrophic events in other systems, from giant ocean waves to sudden surges in power grids. And for optical technologies, it is a step toward lasers that can produce ultra-short, powerful light pulses on command.