We investigate in what turbulent conditions and propagation geometries conventional adaptive optics (AO) can provide improvement in laser applications. Characterizing the optical aberrations is essential to provide the input required for a conventional AO system. In this parametric study we characterize these aberrations by numerically propagating a beacon from an effector into the far field and back using a split-step method involving turbulent phase screens. The beacon’s aberrated field at the location of the effector is sensed assuming a perfect wavefront sensor and subsequently used to pre-correct the effector for its turbulent propagation into the far field. In the far field, beam metrics such as spot size, Strehl ratio and power-ratio-in-the-bucket (PRIB) with and without AO correction applied to the effector are investigated. By varying propagation geometries and turbulent conditions, the dependence of the beam metrics on the propagation scheme is analyzed in detail. Additionally, the dependence of the beam metrics on assumptions in the AO system such as number of Zernike modes taken into account in the correction are studied. The results can be used to identify when AO should be considered given the broader operational context in which a laser system is expected to operate and give insight in accompanying AO considerations.

Fiber lasers have evolved to be the most prominent laser systems for HEL applications due to their combination of ruggedness and excellent beam quality. Systems with multi-kW output power are becoming commercially available, sparking the question of further power scaling and its limits. We will give an overview of current challenges of high power fiber and fiber laser development and point out options for further power scaling in different wavelength regions, also considering the required footprint.

Coherent combination of laser beams is crucial for high-power laser development in various applications, including defense and communication systems. A filled-aperture coherent beam combiner is introduced, which includes polarization-maintaining fiber components, Electro-Optic Modulators, EDFA, a Multi-Plane Light Converter, and a feedback loop based on the Stochastic Parallel Gradient Descent algorithm. The SPGD algorithm allows precise control of the EOMs to achieve stable optical output power. The experimental results demonstrate the proposed approach achieves coherent combination of up to 6 input channels with high efficiency, negligible power loss duration, and precise control over thermal and mechanical perturbations. This technology is directly scalable for different wavelengths.

We report on the experimental demonstration of a fiber laser array composed by 7-elements coherently combined to obtain a total power up to 10kW. The architecture is based on a narrow line single mode master oscillator whose emission is modulated to widen the linewidth up to 47 GHz. The large-linewidth seed is then split in multiple replicas that can be amplified up to 2kW each. Then, a hexagonal array of collimated laser beams is realized by means of a custom opto-mechanical tiled aperture structure. Finally, the beams are overlapped by means of an optical system and coherently combined controlling the single source phases through Lithium-Niobate phase modulators, whose correction signals are computed by a proprietary hill-climbing algorithm. With the developed system it was possible to carry out a characterization campaign to evaluate the vulnerability of different targets, materials and surface finishes, together with the definition of the relevant damage assessment criteria. Some of the most notable results will be presented. The laser Facility, built for this purpose, where the demonstrator has been integrated and tested will be presented too.