How Lasers Work, According to the World’s Top Expert

Whether you’re losing your mind at a Pink Floyd tribute show or playing with your cat, there’s hardly a situation that wouldn’t be made better with a few lasers. “Optical masers” were first described by physicist Charles Townes in the late ’50s and since then they’ve come to define modern life. They’re used to scan groceries at the checkout, read DVDs, guide missiles, perform surgery, and even to produce nuclear fusion.

But if you’re not exactly sure what lasers are or how they work, you’re not alone. WIRED caught up with physicist Donna Strickland, whose work with lasers earned her a Nobel Prize in 2018, and challenged her to explain a laser at five levels of difficulty. Strickland’s explanation at the expert level made total sense, but she also explained it to a child—you know, just in case.

“A laser is a way to get light to be a single color, going in a single direction, with all the waves peaking at the same time so the intensity can get very high,” Strickland says. Unlike light from the sun, which emits photons at all the visible wavelengths, lasers focus their energy on one specific wavelength. This allows them to be powerful enough to cut through steel and precise enough to shave the hair from your skin.

But now that you know what a laser is, you’re probably wondering how it works. The answer, says Strickland, is that bouncing energized photons between two mirrors can cause them to sync up, producing a nice strong beam of a single color. This, of course, leads us to the next natural question about lasers: What is the most powerful possible laser and are we anywhere close to building it?

Strickland has an answer for this and all your other burning questions about lasers. Check it out in WIRED’s new video. You can also watch the next episode (about sleep) on WIRED’s free app for Roku, Apple TV, Android TV, and Amazon Fire TV.

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