MOPA
The most popular way of achieving power scalability is the "MOPA" (Master Oscillator Power Amplifier) approach. The master oscillator produces a highly coherent beam, and an optical amplifier is used to increase the power of the beam while preserving its main properties. The master oscillator has no need to be powerful, and has no need to operate at high efficiency because the efficiency is determined mainly by the power amplifier. The combination of several laser amplifiers seeded by a common master oscillator is essential concept of the High Power Laser Energy Research Facility.
Read more about this topic: Power Scaling