Theoretical and experimental verification of a fast two‐dimensional Gaussian beam mode analysis method

In quasi-optical systems, the beam distortion and the cross-polarisation caused by the offset reflectors get a lot of attention. Also, the distortion was thoroughly studied in previous works. In this study, the authors give the detailed derivations of exact and approximate expressions of cross-polarisation and some simple explanations about energy conversion between co- and cross-polarisations in two-dimensional multi-reflector systems based on Gaussian beam mode analysis (GBMA). In addition two dual-reflector systems with different structures are used to verify the correctness and accuracy of GBMA comparing with physical optics (PO) in commercial software GRASP10. Furthermore, the authors fabricate one of these two systems and give experimental results. Then, they propose a fast analysis algorithm based on the vector addition method to reduce the computation time by eliminating the redundant modes. The efficiency of the proposed fast algorithm is illustrated by the number of modes and the calculation time for each reflection in a tri-reflector system. In addition, the authors also present the computation time of PO in GRASP10 as a reference. With the application of the fast algorithm, the computational efficiency is improved and increases with the number of reflections.