Coherent beam combining of fiber amplifier array output through spectral self-phase conjugation via SBS

Coherent combining of laser beams into a single giant coherent beam with diffraction limited beam quality is one of the most challenging problems in laser physics. The effort given to this problem since the early sixties has been and continues to be enormous since this is the only viable way forward to further power scaling of lasers. The general idea of this approach is to split a single diffraction limited coherent beam into many beams which are then amplified by a parallel array of similar power amplifiers, the combined output from which will be like a single powerful diffraction limited beam. While there have been countless test-of-principle demonstrations at low power it is fair to say that none have had success in real high power systems. The main reason for this is the unavoidable and uncontrollable variation in phase shift (both linear and nonlinear) in the different amplification channels, rendering the combining process essentially incoherent even in a case when the original beam is perfectly coherent. The effect of spectral self-phase conjugation in SBS, recently discovered by the authors, offers a solution to this. We will discuss the basic principles of the effect and its main features and characteristics in regard to its application for coherent beam combining the output from a fiber amplifier array.