Quasi-Optical Mode Converter for a 0.42-THz TE26 Mode Pulsed Gyrotron Oscillator

A quasi-optical (QO) mode converter for a 0.42-THz, TE26 mode, pulsed gyrotron is designed, fabricated, and tested. Based on the geometric optics principle, vector diffraction theory, and the iterative Stratton-Chu method, a computer code is developed to design and optimize the QO mode converter. The scalar Gaussian mode content is about 93.7%, which agrees well with that obtained by the electromagnetic simulation software. The preliminary experiment of the 0.42-THz, TE26 mode QO mode converter shows that a well-focused Gaussian-like beam with 90.4% scalar Gaussian mode content has been observed on the output window by using an infrared video camera. The experimental results agree well with the theoretical prediction.