Study Of Terahertz Structured Beams Generation Based On Phase Retrieval Algorithm

The Terahertz(THz)wave locates between the infrared and microwave,the large number of unique properties of THz wave brings broad applications.THz wave has been applied in Terahertz wireless communication,Terahertz non-destructive inspection,human-body security check and some other regions successfully.Recently,people have made significant advances in THz sources and detectors.But compared with other waveband,the modulation elements for THz filed is relative deficient,it is of great significance to develop THz field modulation elements with high efficiency.Besides,it has been a research hotspot to investigate the generation of THz structured beams,such as Bessel beams and Vortex beams,based on THz filed modulation elements.In this dissertation,we mainly focus on the phase modulation of THz field.We proposed the universal designing method of diffractive THz field phase modulator based on phase retrieval algorithms.We studied the designing methods and applications of 3D-printed diffractive phase plates and full-dielectric metasurface for THz filed phase modulation.3D-printed THz optics elements has many advantages,such as low cost,high manufacturing efficiency etc.It has attracted much attention recent years.We designed diffractive phase plates for THz Gaussian beam shaping based on phase retrieval algorithms and manufactured the phase plates by 3D printing techniques.We generated a THz flat-top beam with high uniformity and energy utilization percentage.During this experiments,we also proposed a new method for building the three dimensional model of phase plates with irregular surface.Besides,we designed a reflective THz active illumination imaging system with big-size flat top beam and THz array-detectors and conducted the initial big-size flat top beam experiments for 0.1THz wave.We also researched on the field propagation behaviors of a Terahertz optic sheet which generated by illuminating the flat-top beam on a cylindrical lens by numerical simulation.Based on the Terahertz optic sheet and THz line-detectors,we designed a new type of THz CT imaging system which is much more efficient compared with the traditions THz CT imaging system.Finally,we studied the full-dielectric metasurface for 0.3THz wave.The full-dielectric metasurface unit cell structure was optimized by Finite Difference Time Domain(FDTD)method.We acquired the amplitude and phase modulation law of designed full-dielectric metasurface unit cell.Based on the phase retrieval algorithm,we designed a THz phase meta-holography which is able to generate “HUST” characters in a fixed plane.We also simulated the whole full-dielectric metasurface by FDTD,the simulation results are consistent with the theoretic design.Furthermore,we studied the propagation behaviors of THz wave modulated by the meta-holography.