Terahertz Devices Based On Surface Plasmon Enhancement

The terahertz spectrum of matter contains rich physical and chemical information and therefore it is of vital importance to study terahertz spectrum for the exploration of material structure.Recently,photoconductive antennas were normally employed as terahertz devices in most of commercial terahertz emitters.However,the terahertz photoconductive antennas are still facing the problem of low output power,which limits its applications where high power terahertz are required for nondestructive testing(NDT),such as NDT of aircraft composite materials etc.In recent years,development of high-power terahertz emitters(or terahertz photoconductive antennas)has become a hot topic.With the development of micro-nano technology,the terahertz devices based on surface plasmon enhancement have become an important research direction.In order to solve the problem of low output power of terahertz photoconductive antenna,the principle of terahertz photoconductive antenna was studied;the factors influencing the radiation strength of terahertz photoconductive antenna were discussed;a novel terahertz photoconductive antenna based on surface plasmon enhancement was proposal in the present work.The work is as follows:The electromagnetic field and semiconductor theory of terahertz photoconductive antenna were systematically introduced.The basic equations of electromagnetic field computation,the constitutive relation of the medium,the wave equation and several electric displacement filed models were illustrated.The distribution function of the semiconductor carrier concentration and its basic equations of motion were described,and the principles of the generation and recombination of carriers in semiconductor was introduced.COMSOL Multiphysics was used to calculate the finite element simulation of the conventional photoconductive antenna.The terahertz photoconductive antenna model was established and it was used for the analysis of terahertz radiation strength and its variation trend with the bias voltage and laser power.The simulation results showed that the terahertz radiation strength was approximately proportional to the bias voltage;the terahertz radiation strength was enhanced with the increase of the laser power,and there was a saturation trend.A terahertz system was designed and built.The basic principle of the experiment system was introduced together with the main hardware.The experimental results showed the terahertz waveform,also demonstrated the relationship between terahertz radiation strength and bias voltage,and the relationship between terahertz radiation strength and laser power.The experimental relationship results were basically consistent with the simulation.Therefore,the feasibility of the simulation model to predict the strength of terahertz radiation strength was verified.Aiming at the problem that the output power of conventional terahertz photoconductive antennas is low,a metal-array terahertz photoconductive antenna based on surface plasmon enhancement was proposed.The enhancement mechanism of the surface plasmon-enhanced photoconductive antenna was illustrated by analyzing the nulti-physics field of the photoconductive antenna.The simulations of surface plasmon-enhanced terahertz photoconductive antenna and conventional terahertz photoconductive antenna were calculated.The results showed that the terahertz radiation strength of surface plasmon-enhanced terahertz photoconductive antenna was significantly stronger than that of the conventional terahertz photoconductive antenna.These results provided an important reference for the design of surface plasmon-enhanced terahertz photoconductive antennas.