Output coupler
From Wikipedia, the free encyclopedia
1. Active laser medium
2. Laser pumping energy
3. High reflector
4. Output coupler
5. Laser beam
An output coupler (OC) is a semi-transparent mirror used in lasers to extract a portion of the laser beam from the optical resonator.
Lasers operate by reflecting light between two 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 to the target.
There are two important properties of the output coupler:
- Shape
- The output coupler may be either flat or curved, depending on the desired properties of the optical cavity. The shapes of the end mirrors and the distance between them determines the transverse modes of the cavity.
- Depending on the gain of the medium, the amount of light the output coupler needs to reflect back can vary widely. Helium-neon lasers require around a 99% reflective mirror to lase, while nitrogen lasers have an extremely high gain (they are "superradiant") and do not require any output coupler (0% reflective). The reflectance of any output coupler will change based on the wavelength of light, so this value is often given at the laser's operating frequency.
