What is the primary function of a gain medium in lasers?

The gain medium is a crucial component in a laser's operation, primarily responsible for amplifying light. This happens through a process called stimulated emission, where the gain medium, composed of specific atoms or molecules, absorbs energy and subsequently emits light. When external energy is supplied (often from a pump source), it excites the atoms in the gain medium, causing them to emit additional photons. This amplification of light is essential for producing the intense, coherent beam characteristic of lasers.

In contrast, while filtering light wavelengths, reflecting light, or adjusting focus may be functions of other components within a laser system, they do not define the primary role of the gain medium. The amplification of light is the fundamental process that allows lasers to produce a concentrated beam, making it the central function of the gain medium in laser technology.