Study on a gyrotron quasi-optical mode converter for terahertz imaging

Abstract

In this paper, a quasi-optical mode converter for terahertz imaging is presented. This design  is based on a 0.22 THz TE₀₃ gyrotron oscillator. It includes a Vlasov launcher, an elliptical reflector and a parabolic reflector, which is used to convert TE₀₃ cylindrical waveguide mode to a Gaussian-like beam. The quasi-optical system is analyzed in terms of geometric optics theory and the vector diffraction theory. Numerical optimization code is programmed by MATLAB software for analyzing the quasi-optical system. Simulation results show that the power transmission efficiency of the operating cavity mode to a fundamental Gaussian distribution is 82.14%, the output Gaussian beam can be propagated over 0.8 m without divergence and the scalar Gaussian mode content is 98.2%. A cold test experiment platform is built up to verify the design based on numerical calculation. In experiment, the scalar Gaussian mode content of 97.0% is measured which shows good agreement with numerical calculation.

KEYWORDS:

• Quasi-optical mode converter
• Gaussian beam
• terahertz imaging
• gyrotron

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data available on request from the authors.

Additional information

Funding

This work was supported in part by the National Key Research and Development Program of China [grant number 2019YFA0210202], in part by the National Natural Science Foundation of China [grant number 61971097], in part by the Sichuan Science and Technology Program [grant number 2018HH0136].

Notes on contributors

Chengxin Zhang

Chengxin Zhang is a Ph. D. candidate at University of Electronic Science and Technology of China. His main research area is terahertz imaging based on high power gyrotron.

Wenjie Fu

Wenjie Fu received the B.S. degree in applied physics, M.S. degree in plasma physics and Ph.D. degree in physics electronics from the University of Electronic Science and Technology of China (UESTC), Chengdu, China, in 2003, 2006 and 2010 respectively. In 2006, he joined the Terahertz Science and Technology Research Center, UESTC, where he is currently an Associate Professor. His technical interests include gyrotron, terahertz application and plasma physics.

Yang Yan

Yang Yan was born in Sichuan, China in 1965. He received the B.S. degree in 1986 and the Ph.D. degree in 1995 from the University of Electronic Science and Technology of China. Currently, he is a Professor in University of Electronic Science and Technology of China. His research interests are in the field of high power terahertz radiation sources and applications.