A technique to enforce operation of a Laser on a certain Frequency by injecting Light with that frequency into the laser cavity.
The high Output Power is generated with a power Laser">High Power Laser (not with an amplifier), called the slave laser, the Noise level of which is strongly reduced by injecting the output of a low-noise low-power Master Laser (or seed laser) (usually a bulk laser) through a partially Transparent cavity mirror. Provided that the frequencies of the master laser and the free-running Slave Laser are sufficiently close, the injection forces the slave laser to operate only on the injected frequency with relatively little noise. The higher the injected power, the larger the allowable frequency offset between the lasers. Close to quantum-limited Intensity and Phase Noise can be achieved with this approach.