How do lasers produce such a powerful beam of light?

The answer

Lasers work through stimulated emission: when a photon of exactly the right energy hits an excited atom, it forces the atom to emit a second identical photon traveling in the same direction, with the same wavelength and phase. By bouncing photons back and forth between mirrors inside a gain medium, this process cascades exponentially. The result is a beam of coherent light where all photons are perfectly synchronized, giving lasers their extraordinary focus, intensity, and precision.