mode-locking

Mode-locking is a technique used in lasers to produce extremely short pulses of light. It works by synchronizing the phases of multiple laser modes, which are different wavelengths of light that can oscillate within the laser cavity. When these modes are in phase, they constructively interfere, creating a very short, intense pulse of light.1

This process relies on the principle of stimulated emission, where an incoming photon triggers an atom to release an identical photon. In a laser, this creates a cascade of coherent photons. By controlling the laser cavity and the energy levels within the laser medium, a condition called population inversion can be achieved, where higher energy states are more populated than lower ones, enabling stimulated emission to dominate.2

Mode-locking allows lasers to generate pulses with durations as short as femtoseconds (10^-15 seconds), enabling the study of ultra-fast phenomena like chemical reactions.1