On the design of high conversion efficiency quasi-optical mode converter for 140 GHz high-power gyrotron applications

A high conversion efficiency quasi-optical mode converter prototype is designed for 140 GHz TE_22，6 applications. The Denisov launcher is designed based on the periodic perturbation concept，leading to primary radiation field with low edge diffraction. Full-vector physical optics integration solver is used to model and analyze the 3-mirror system. And the 3-mirror iterative phase correction is applied based on the co-polarization field component，so as to achieve high-quality mode conversion. Specifically，the correction of the 1^st mirror sufficiently refines the non-ideal radiated fields from the launcher. It is then validated by numerical investigations that，comparing to the original quaritic mirrors，the phase-shaped mirror system leads to excellent conversion performance. The Gaussian content（η_v）of the output fields rises from 92. 7% to 99. 6%，while the power transmission efficiency（η_p）reaches 98. 8%.