Abstract.  A plasma generation by laser-matter interaction is a powerful tool in the field of plasma research and applications. Recently, laser-induced plasma has been given a great attention, from material science to plasma deposition. However, current laser technologies have difficulty on increasing the laser power because of the thermal problems of the laser medium. The beam combination laser can overcome the thermal problems as it coherently combines multiple existing lasers without additional need for thermal management. H. J. Kong et al. developed the beam combination laser using the phase controlled stimulated Brillouin scattering phase conjugate mirrors (SBS-PCMs) has been developed. The key factor for achievement of the coherent combination is to overcome the randomness of the SBS phase. To lock/control the phases of the SBS waves, H. J. Kong et al. proposed and have developed a new phase control technique, so called “the self phase control technique.” The phase of each sub-beam can be controlled independently with the simplest arrangement. Thus, energy scaling is easily achieved by just increasing the number of the combined beams. The effective of this technique has been demonstrated experimentally over a decade.

In this work, the phase control of a tiled four-beam combination laser is successfully performed with amplification. The relative phase fluctuations are measured from the interference pattern that is generated from the combined output beam and the reference beam. Without amplification, the combined output energy is 9.9 ± 0.5 mJ when the input energy is 32.2 ± 0.3 mJ. In this case, the standard deviations of the phase differences are measured to be λ/116, λ/38.9, λ/31.5, and λ/39.5, during 2,500 shots (250 s). When the amplifiers are operating, the combined output energy is 169 ± 6 mJ corresponding to the total gain of 5.3. In this case, the standard deviations of the phase differences are measured to be λ/68.8, λ/26.5, λ/28.0, and λ/26.1, during 2,500 shots (250 s).