High-efficiency 2D Grating Design for the Magneto-Optical Trap: Enhancing Intensity Balance and Reducing Optical Complexity

Abstract: Diffraction gratings integrated into an atomic, molecular, and optical (AMO) setup offer a compact and efficient route toward atom cooling and trapping, thus preparing magneto-optical traps (MOT) for insertion into future scalable quantum systems. Here, we propose and numerically validate a two-dimensional (2D) diffraction grating that satisfies the required optical conditions for laser cooling, namely, radiation pressure balance, specular reflection cancellation, and circular polarization handedness reversal upon diffraction, thus achieving an optical molasses, a necessary condition in MOT. Using Rigorous Coupled Wave Analysis (RCWA) and a Genetic Algorithm (GA), we optimize the grating's geometry to maximize key figures of merit. The grating consists of a 2D square lattice of nanoholes and is designed to diffract normally incident 780 nm circularly polarized light into the four first orders, each with a diffraction efficiency of 0.24, of which 99.7% has the correct circular handedness. Our 2D diffraction grating can enhance the performance of GMOTs employing 2D gratings by improving the axial radiation pressure balance and providing a high degree of circular polarization. Furthermore, we investigated the robustness of our 2D grating to ensure high manufacturing resilience.