Design And Manufacture Of Flexible Terahertz Absorbers

The terahertz(THz)wave,which is in the transition region of electronics to photonics,has many unique properties,and can be widely used in THz imaging,communication,material detection and other fields.However,the development and applications of THz technology are strongly limited,due to the relatively backward progress of THz emission and detection technologies.The Salisbury screen absorber is an absorber with a simple structure and easy to be fabricated,which can achieve nearly perfect absorption in specific frequency bands.Therefore,it is possible to effectively promote the development of THz technology by exploring and studying the Salisbury screen THz absorbers.In this dissertation,a new type of flexible Salisbury screen absorber based on organic THz absorption materials is designed and fabricated,and its absorbing principle and THz response rules are investigated.The main contents are as follows:(1)Organic 4-N,N-dimethylamino-4?-N?-methyl-stilbazolium tosylate(DAST)was chemically synthesized,purified and characterized.The dielectric constants of DAST single crystal along a axis and b axis in the range of 0-10 THz were studied based on the Lorentz model.Furthermore,based on this model,the refractive index,extinction coefficient,and the alternating current conductivity of DAST single crystal along a axis and b axis in the range of 0-10 THz were calculated by Matlab software.(2)An organic nonlinear optical material DAST was used as the resistance layer for novel Salisbury screen absorbers for the first time.The absorbing characteristics of the Salisbury screen absorbers based on DAST single crystal were theoretically studied through the transfer matrix method,transmission line model,and multiple reflection theory,by which the analytical solution of its absorption characteristics was obtained.Moreover,the absorbing characteristics of the absorbers under different DAST single crystal thicknesses were obtained through Matlab programming calculation.(3)The calculated dielectric parameters of DAST single crystal along a axis and b axis were imported into the CST simulation software.Then,the CST simulation software was used to calculate the absorbing characteristics of the absorber along the a axis and the b axis of the DAST single crystal under normal incidence condition,and the absorption characteristics of TE and TM modes under different angles of incidence.(4)A flexible polymer(polytetrafluoroethylene,PTEF)film,which does not absorb THz wave,was used as the dielectric layer of the Salisbury screen absorber.A Salisbury screen absorbers based on DAST polycrystalline thin film were successfully fabricated by spraying DAST methanol solution and annealing under nitrogen.Subsequently,the THz absorption spectra of the as-fabricated absorbers were measured by THz-TDS.The measured results demonstrate that when the thickness of DAST polycrystalline thin film increases from 2 ?m to 4 ?m,the absorbance of the Salisbury screen absorber at 1.1 THz increases from 29.8% to 68.8%,which are very close to the CST simulation results.(5)The piezoelectric and THz absorption properties of another organic nonlinear material m-Nitroaniline(mNA)were studied,and the prospect of THz absorption using mNA as resistor layer for Salisbury screen absorber was also explored.