What is the primary function of a resonant cavity in a laser system?

The primary function of a resonant cavity in a laser system is to create photons that resonate and emit them selectively. Within a laser, the resonant cavity is formed by mirrors that reflect light back and forth, allowing certain wavelengths of light to build up in intensity through constructive interference. This setup promotes the amplification of specific photon wavelengths while suppressing others, which is critical for producing a coherent and monochromatic light output—hallmarks of laser light.

As photons bounce between the mirrors, they pass through the gain medium, where they can stimulate the emission of additional photons. The resonance condition ensures that only photons matching the cavity’s specific modes can effectively bounce back and forth, reinforcing their intensity. This selective emission is what gives lasers their unique properties compared to other light sources.

The other options do not accurately represent the core function of the cavity. While absorbing photons or amplifying all light sources may be associated with specific processes in different contexts, they do not reflect the fundamental purpose of the resonant cavity in a laser system. Dispersing light uniformly also diverges from the core laser functionality, which relies on the coherent and directed nature of the emitted light.