You can squeeze light between two mirrors like a spring in a vise. It bounces back and forth, growing denser: that's how you get ultra-bright beams. But there's a limit: at too high a brightness, the mirrors start to shake. The light rocks them the way wind rocks a swing, and some energy leaks into that jitter.
Physicists measured where the trembling comes from. It turns out it's not the mirror mounts that vibrate, but the mirrors themselves, inside, like a bell that rings after being struck. The shaking frequency is millions of oscillations per second. The researchers picked mirrors that damp out quickly, the way a pillow absorbs a punch. And then the beam became brighter than ever before in such a trap.
Such bright light is needed for electron microscopes that see individual atoms and for traps that hold molecules still. Previously, the mirror shaking was the main obstacle — now it's been tamed, simply by choosing the right material.
In the experiment, the mirrors shook at a frequency of several million times per second — about a hundred times higher than the sound of the highest note on a piano.
Stories about super-powered lasers often forget that optics can't withstand their own light. Here, the hero isn't the beam but the mirror that learned not to shake.