Which statement best describes the Optical Cavity in a laser?

• A. It contains the Active Medium and comprises a fully reflecting mirror and a partially reflecting mirror
• B. It cools the laser system
• C. It houses the power supply
• D. It emits radiation directly

Answer: (A)

The optical cavity acts as a feedback loop that makes the light amplify inside the laser. By placing the gain (active) medium between mirrors, photons are bounced back and forth through the medium, so each pass stimulates more emission and the light builds up to a strong, coherent beam. In a typical cavity, one mirror is highly reflective to keep light circulating, while the other is partially reflective to let a portion escape as the laser output. This arrangement not only sustains lasing but also helps set the laser’s output and the resonant light modes. The cavity isn’t for cooling, it doesn’t house the power supply, and it doesn’t emit radiation by itself—the emission is generated in the active medium and shaped by the mirrors.