Characterization Of Terahertz Band-pass Filters Fabricated By Femtosecond Laser Micromachining

Electromagnetic waves in different bands have a wide range of applications in human life,such as microwave communication,infrared monitoring and X-ray imaging.Terahertz refers to a frequency range between the millimeter wave at 0.1 THz and the far-infrared light at 10 THz,has some unique properties such as coherence,low energy,penetrability,instantaneity and so on,which has a great application prospect in the field of nondestructive testing.New terahertz sources are being created with more and more researchers interested in terahertz technology.However,compared with the rapid development of terahertz radiation source and detection technology,the development of terahertz functional devices,a key component for terahertz applications,still lags behind.Terahertz functional devices include filters,polarizers,and terahertz switches,play an important role in terahertz applications.Therefore,how to make low-cost and high-performance terahertz device is an important research field.There are four types of terahertz filters existed,including frequency selective surface(FSS),Metamaterial,waveguide filter and photonic crystals.The frequency selective surface and metamaterial are the most widely used.However,because the wavelength of terahertz is very short,and the structure size of these devices is small,ordinary processing techniques are usually not qualified.Femtosecond laser micromachining is widely used in the manufacture of microelectromechanical systems with its high precision,low cost and "cold" processing characteristics.Compared to the traditional ink-jet printing,photo-lithography,the chemical vapor deposition and other micro processing technologies,it is simple,less-process,low-cost,via a single ablation operation,suitable for all kinds of microstructure and high precision processing,for example,metamaterial,frequency selective surface and terahertz functional devices with periodic structures.Firstly,I introduce the future prospects of terahertz technology and the current research progress of terahertz filters.Secondly,the analysis method of terahertz filter based on frequency selective surface and the principle of femtosecond laser processing are introduced.Then,the construction of femtosecond laser micromachining system and the processing procedures of terahertz frequency selective surface are introduced.On this basis,the performance and mechanism of single layer and double-layer filters are studied and demonstrated.Finally,we give a brief introduction on the design of terahertz absorbing materials based on metamaterials.The major completed tasks include:(1)Set up the femtosecond laser micro-processing system,and write automatic processing program,and fabricate THz band-pass filters using a 10?m thick aluminum foil.(2)Use the Finite Difference Time Domain(FDTD)method to simulate the on the performance of terahertz filter with different structural parameters;Measure the performance of single-layer and double-layer filters using a terahertz time-domain spectroscopy,and investigate the effect of surface plasmon polaritons(SPPs)on the double-layer filters.(3)Based on the principle of absorbing materials in the microwave band,the metamaterial absorbing structure in the terahertz band was designed,and the preliminary research work was conducted for the future terahertz band stealth.