Design And Implementation Of Freeform Lenses And Axicon In THz Band

Terahertz wave has been widely used in the field of imaging and nondestructive detection because of its unique transmission and low energy.In order to improve the quality of imaging,this paper explores the design and manufacturing methods of freeform lens and freeform axicon,and verifies them from three aspects of theory,simulation and experiment,which proves that the designed lens and axicon can be used in engineering practice.The main contents of this paper are as follows:Firstly,the development of terahertz wave imaging and the advantages and current situation of freeform lens imaging are introduced.Then,a design method of freeform lens based on numerical calculation is introduced,and its principle is deduced,which proves its rationality in theory.After that,the simulation software and 3D printing technology for testing lens performance are introduced,and it is demonstrated that 3D printing technology can be used to make THz freeform lens.Finally,the experimental system for testing the lens performance is introduced.Three kinds of freeform lenses with a focal length of 100 mm in terahertz band are successfully designed by using the above design method and with the help of software Mathematica,and they are made by 3D printing technology.In order to verify the focusing performance of the lens,in the simulation software,the collimating beam is incident on the designed freeform lens,and the focal length of the beam is about 100 mm,and the beam waist radius is small.After that,the experimental system is set up for experimental verification,and the results are close to the simulation,it is proved that the designed lens can be used to focus terahertz wave.Finally,using the experimental system to scan the resolution plate,the imaging effect of the freeform lens is better than that of the conventional spherical lensThen the Bessel beam of the non-diffracting beam and the two-axicon structure for increasing the non-diffractive distance are introduced.Then a design method offreeform axicon is introduced.The axicon whose incident surface is freeform surface is designed by this method,and it is made by 3D printing.The conventional axicon in the two-axicon structure is replaced by the freeform axicon.The simulation and experiment results show that the non-diffractive distance of the beam is not shorter than that of the conventional axicon,and the projection distance is longer than that of the conventional axicon.In this paper,two approximate design methods are used to design the freeform lens for focusing and the freeform axicon for generating non-diffractive beam.Simulation and experiment show that its performance is not inferior to that of conventional lens and axicon.