Optimization of brightness in a Nd:YAG laser by maximizing the single-mode power factor with an intra-cavity spatial light modulator.

We report a simple and effective approach for designing resonators with high brightness and high mode discrimination based on optimizing the single-mode power factor of the fundamental mode, which represents the total power extracted by the fundamental mode from the gain medium. By optimizing the single-mode power factor of the fundamental mode, the cavity can be designed to operate in mono-mode, increasing mode purity and improving brightness significantly. Our method is verified on a digital laser with a spatial light modulator as the rear mirror, and the loaded phase profile is acquired by a simulated annealing algorithm. As a result, the optimized resonator with a Fresnel number of 7.2 operates in a single fundamental mode, and the brightness of the output beam yields 240% and 276% improvement, compared with conventional plane-plane and plane-concave resonators, respectively. This approach is ready to be applied to more sophisticated mode selection and may serve as a general method for designing cavities with high efficiency and high brightness.