Output coupler
![Principal components of a laser:1. Active laser medium2. Laser pumping energy3. High reflector4. Output coupler5. Laser beam](/Images/godic/202501/31/Laser.svg0514.png")
An output coupler (OC) is a partially reflective mirror used in lasers to extract a portion of the laser beam from the optical resonator.
Lasers operate by reflecting light between two or more mirrors which have an active laser medium between them. The medium amplifies the light by stimulated emission. For lasing to occur, the gain of the active medium must be larger than the total loss, which includes both unwanted effects such as absorption, and the intentional release of energy through the output coupler. In other words, the laser must attain threshold.