Population Inversion

Population inversion occurs when a greater number of atoms or molecules in a system are in an excited state rather than in their lowest energy state. Under normal conditions, most particles stay in lower energy states. Achieving population inversion is essential for laser operation, as it allows stimulated emission of photons, producing a coherent, focused beam of light. This process typically requires external energy input (pumping) to excite particles selectively. In essence, population inversion creates the right conditions for light amplification and laser action by reversing the usual energy distribution among particles.