Rami Arieli: "The Laser Adventure" Chapter 3.4 page 1
3.4 Output Coupler
Output coupler is a means to transmit electromagnetic radiation out of the laser.

The standard output coupler uses a partially reflecting mirror as explained in chapter 3.3. The part of the beam which is not reflected back into the active medium, is transmitted out.

In a continuous wave laser (in which the radiation is emitted continuously), most of the radiation is reflected back into the cavity, and only a few percent is transmitted out.

In certain pulsed lasers most of the radiation within the cavity at a specific moment is transmitted out in a pulse (see chapter 7.4).