Development and Optimization of a VUV Laser Alignment System for Antihydrogen Cooling in the ALPHA Experiment

This report presents the development and optimization of a vacuum ultraviolet (VUV) laser alignment system for antihydrogen cooling within the ALPHA experiment at CERN. To enable Doppler laser cooling at 121.6 nm via the 1S–2Pf transition, a third-harmonic generation process is employed to produce Lyman-alpha radiation from a 365 nm input laser. Optical alignment is the most challenging step; our goal is to automate it and maximize the spatial separation between the 121.6 nm and 365 nm beams, thereby improving the stability and efficiency of the nonlinear conversion. This project involved surveying the existing optical system, implementing a ray-tracing model using Optiland, and optimizing beam separation and focusing by adjusting the mirror angles. In parallel, a detailed characterization of the picomotor-driven mirrors was performed, revealing nonlinearities and hysteresis that pose challenges for automation. Feedback-based solutions were explored, but were hindered by hardware limitations. As an alternative, a passive alignment system using irises on translation stages was proposed and integrated. The resulting methodology enhances reproducibility and streamlines the alignment process, laying the groundwork for the future implementation of a closed-loop optimization system.