Research On Terahertz Spectroscopy Properties Of The Surface Micro-nano Structures

Terahertz(THz) electromagnetic waves, which have unique properties and great potential in scientific research, have become a popular research direction in fundamental and applied science. Recent progresses in ultrafast laser technology and microstructure fabrication technology have dramatically accelerated the development of THz functional devices, make it as important as sources and detectors in many THz systems. However, the greatest obstacles in THz functional devices are the lack of materials that naturally respond well to THz radiation, while the microwave and optical devices has been unable to meet the application requirements in the THz regime. The THz absorber, with high absorption and low reflection capabilities, has become a crucial component in the THz function devices.In this thesis, firstly, based on the simulation method of the CST simulation software and the preparation process of the periodic structures, we explore the THz transmission characteristics of the metal hole array structures. According to the recent research progresses in THz absorber, aiming at the key problem of the intrinsically narrowband, we mainly design and fabricate two types of broadband THz absorber, the L-shaped dual-broadband THz metamaterial absorber and the silicon-based broadband THz absorber. The structural parameters are optimized through theoretical analyses and numerical simulations. The following are the main work and progress:1. Based on the metamaterials of a periodic array of L-shaped resonators, a highly efficient dual-broadband THz absorber has been designed and fabricated. This absorber is consists of an aluminum(Al) metamaterials layer and an Al ground plane separated by a silicon dioxide(SiO2) dielectric film, the film thickness of the Si O2 film can be precisely controlled and the large-area uniformity can also be achieved. Simulation results indicate that the thickness of the dielectric layer and the structure parameters of the resonant are obvious influence on the absorption spectra. The optimized absorber can achieve over 90% absorption in two broad frequency ranges from 2.9THz to 4.3THz(absorption bandwidth 1.4THz) and from 7.4THz to 8THz(absorption bandwidth 0.6THz), which has wider absorption bandwidth compared with the conventional metamaterial absorber. Furthermore, such broadband metamaterial absorber has been fabricated and measured.2. Using binary antireflection grating structures on a heavily doped n-type silicon substrate, an easy fabricating and highly efficient silicon-based broadband THz absorber has been designed and fabricated. This absorber can be divided into two layers: the grating layer and the substrate layer. Simulation results indicate that the grating parameters, doping concentration and doping types are obvious influence on the absorption spectra. The optimized absorber, by utilizing the two absorption peaks are merged into one broadband absorption spectrum, can achieve over 90% absorption in a broad frequency range from 2.5THz to 8THz and its relative absorption bandwidth is 104.8%. Furthermore, such silicon-based broadband absorber has been fabricated and measured.