- A new kind of laser light—called an optical frequency comb—can be used to measure frequencies of light and intervals of time more precisely and easily than ever before.
- The comb is made of a train of evenly spaced, ultrashort laser pulses with a spectrum that looks like tens of thousands of “teeth.”
- Applications include a more precise atomic clock, ultrasensitive chemical detectors, laser control of chemical reactions, higher-capacity telecommunications using optical fibers and improved lidar (light detection and ranging).
In the blink of an eye, a wave of visible light completes a quadrillion (1015) oscillations, or cycles. That very large number presents both opportunities and a challenge. The opportunities promise numerous applications both inside and outside of laboratories. They go to the heart of our ability to measure frequencies and times with extremely high precision, a skill that scientists rely on for some of the best tests of laws of nature—and one that GPS systems, for instance, depend on. The challenge has centered on the impossibility of manipulating light with the techniques that work so well for electromagnetic waves of much lower frequencies, such as microwaves.
Now, thanks to a decade of revolutionary advances in laser physics, researchers have at hand technologies that can unlock the latent potential that visible light’s high frequencies previously kept us from realizing. In particular, scientists have developed the tools to exploit a type of laser light known as an optical frequency comb. Like a versatile ruler of light with tens or hundreds of thousands of closely spaced “tick marks,” an optical frequency comb provides exquisitely precise measurements of light. Such a comb can form a bridge spanning the huge frequency gap from microwaves to visible light: very precise microwave measurements can, with an optical comb, produce equally exact data about light.