Lasers: Synchronized Light

A laser is what happens when you force trillions of atoms to emit photons in perfect lockstep. Ordinary light has photons with random wavelengths, directions, and timing. Laser light is monochromatic (one color), coherent (all waves in phase), and collimated (barely spreads out).

The trick is stimulated emission: one photon triggers an excited atom to release an identical photon, those two trigger two more, and mirrors bounce the light back and forth to amplify the cascade. The result is an intense beam of a single precise wavelength.