Iteration-free, simultaneous correction of piston and tilt distortions in large-scale coherent beam combination systems.

Coherent beam combination (CBC) holds promise for scaling the output power of the laser system while maintaining good beam quality. Owing to the thermal effect and mechanics instability, piston and tilt distortions always exist and affect the performance of the combined beam. To ensure the constructive interference in the far-field, dynamic correction of the distortions is highly required. Here, we propose an approach for the simultaneous correction of piston and tilt distortions in CBC systems. Based on the position and interval information of the near-field interference fringes, the theoretical expressions for the relative piston phase and tilt errors of each array element are derived, indicating that dynamic distortions in CBC systems can be directly calculated and then corrected by employing phase control servos. To demonstrate the feasibility of the proposed approach, Monte-Carlo Simulations have been carried out for different perturbative environments. Our results indicate that both piston phase and tilt errors can be calculated and compensated accurately (λ/25 and 0.11μrad) by the proposed approach even in 169 beamlets, which also has high tolerance for defocus errors. This work could provide valuable reference on the practical implementation of high-power, phase-locked fiber laser array systems.