A Laser which is injection-locked to another laser.

A slave laser is a laser where the Noise properties are greatly improved by Injection Locking with a low-noise low-power master laser. The term results from the fact that the Master Laser dictates the optical Frequency and phase to the slave laser. An electronic servo System is usually used to keep the frequency of a Resonator Mode of the slave laser close enough to the frequency of the master laser to allow for frequency locking.