Research On Terahertz Source Based On Plasmons Of Micro-nano Structure

Terahertz waves have extremely high application value.The study on terahertz sources has become a key topic in terahertz science and technology research at home and abroad.Based on the excitation of terahertz plasmons,this thesis studies the modulation of surface plasmons on metal by nano defects,the conversion of plasmons on metal micro-nano structure into terahertz radiation fields and the theory of terahertz plasmons generation and amplification in high electron mobility transistor micro-nano structures,which provide guidance for the research on the miniaturized 1-5 terahertz radiation sources.The main research contents and achievements of this thesis are as follows:1.The frequency regulation mechanism of metal surface plasmons is studied.Based on the simulation method of light wave excited metal surface plasmons,the influence of introducing single and discrete periodic defects into metal on the frequency of surface plasmons is studied.The results show that periodic nanoscale defects are introduced into the metal to reduce the density of metal free electron gas,change the metal equivalent permittivity,modify the metal Drude model,reduce the frequency of surface plasmons,and realize the regulation of surface plasmons frequency.The defect boundary will limit the movement of free electron gas and has a significant impact on the dielectric constant.Using the adaptive Drude model to describe the dielectric constant of the metal structures with periodic defects will help guide the design of surface plasmons device,which is of great significance to the application of the surface plasmons.2.An asymmetric subwavelength periodic hole array excited by electrons is used to generate spoof surface plasmons and converted to Smith-Purcell coherent radiation in the terahertz band.Based on the theory of subwavelength hole array spoof surface plasmons excited by free electron,an asymmetric subwavelength periodic hole array structure is proposed by combining two subwavelength hole arrays with different periods,which can converte the spoof surface plasmons excited by free electron into Smith-Purcell coherent radiation,and the radiation mechanism of spoof surface plasmons conversion is explained.Based on the radiation mechanism,1.25THz micro hole array terahertz coherent radiation source is designed.The results show that the asymmetrical subwavelength periodic structure can achieve terahertz radiation at the design frequency,and the coherent and tunable terahertz Smith-Purcell radiation can be obtained by adjusting the period and hole size of the asymmetrical subwavelength hole array.3.The oscillation amplification of terahertz plasmons in high electron mobility transistor(HEMT)is studied.Based on the theory of the instability of terahertz plasmons in high electron mobility transistors excited by dc current,the nonlinear hydrodynamic equation of the two-dimensional electron gas layer is solved.The amplification of terahertz plasmons in the transistor is simulated with the actual structure parameters,and the effects of electron concentration,drift velocity,relaxation time,and channel length on the performance of the terahertz wave under the actual parameters of the AlGaN/GaN HEMT are also demonstrated.The results show that the conditions for the amplification of terahertz plasmons become more stringent under the influence of internal friction,which from?_t(27)2?(?_t is the electron transit time and?is the electron relaxation time)to?_t(27)1.78?.The HEMT structure with high drift speed,high electron concentration and large relaxation time is of great significance to the development of 1-5THz Terahertz source.4.The combination of vacuum electronics and terahertz plasmons in HEMT structure is proposed to develop 1-5THz amplifier based on the beam-wave interaction amplification mechanism.Based on the Pierce theory,the interaction between electron and terahertz plasmons in HEMT structure is studied,and the small signal theory of beam-wave interaction is derived.The small signal gain is calculated according to the dispersion equation.The results show that when the electron drift speed is slightly faster than the terahertz plasmons,the gain of 1.22dB per wavelength at 2.5THz can be obtained,which provides a theoretical prediction for the terahertz amplifier based on the combination of vacuum electronics and HEMT structure.