The chapter opens with an introduction to the semiclassical theory of light-atom interactions and optical resonators.

Two or more mirrors that form an optical resonator.

Such a gain medium, along with an optical resonator, is at the heart of a laser or maser.

This can be used to produce a laser beam containing only a single transverse mode of the laser's optical resonator.

The optical resonator serves to resonate at least one of signal and idler waves.

These photons are fed back into the laser medium, usually by an optical resonator.

Q-switching is achieved by putting some type of variable attenuator inside the laser's optical resonator.

The mirror loss is due to photons escaping through the mirrors of the optical resonator.

This same method can also be used to find the fundamental mode size of a stable optical resonator.

Ring resonators and whispering galleries are examples of optical resonators that do not form standing waves.