过模表面波振荡器输出太赫兹波模式的影响因素分析

Simulation and Optimization of Terahertz-Wave Output from Overmoded Surface Wave Oscillator

采用轴向电场分解与PIC(Particle-in-cell)模拟相结合的方法,研究了二极管参数、引导磁场和输出结构等因素对0.14 THz过模表面波振荡器输出太赫兹波模式的影响。当太赫兹波实现稳定输出时,其模式成分和相对相位差基本不受二极管电压的上升沿、幅度和引导磁场大小的影响,除非振荡器的工作状态发生了明显改变,但它们对阳极半径和阴阳极间距的变化较为敏感。在较小的二极管电压、阳极半径或阴阳极间距下振荡器能获得一定成分的TM01模太赫兹波输出。输出结构决定了输出太赫兹波的模式成分。通过合理设计锥形输出结构的参数,能够实现相同功率水平下的纯净TM01模输出,简单有效地解决过模表面波振荡器的多模输出问题。

The impact of the diode characteristics, guiding magnetic field, and output structure on the output mode of terahertz-wave from 0.14 THz overmoded surface-wave oscillator were modeled, analyzed by Fourier-Bessel expansion of the axial electric field, and simulated with particle-in-cell code. The calculated results show that at a stable output, the mode contents and phase differences involved depend strongly on the anode radius and cathode-anode distance, but weakly on the rising edge and amplitude of input diode voltage and guiding magnetic field. We found that the output structutre detemines the mode content, and that reduction of the diode voltage, anode radius, and athode-anode distance results in an increase of the TM01 mode content while the power remian unchanged. We suggest that the pure TM01 mode content may be obtained by optimizing the conical output structure of the overmoded surface wave oscillator.