| With the rapid development of science and technology,countries use for their own construction of equipment and devices more and more advanced.Infrared tracking and detection systems require high optical performance and need to maintain a high transmission rate in the infrared band.As a wide band gap transparent material with excellent optical properties and physicochemical properties,zinc sulfide is widely used in infrared windows.As a transparent material with excellent optical and physicochemical properties,zinc sulfide is widely used in detection systems,so it is especially important to study the surface transmission properties to improve its transmission rate in the infrared band.The traditional method is to prepare antireflection films on the surface of zinc sulfide,but the films are easy to peel off and have limited effect on broad-spectrum,large-angle incident infrared signal de-reflection.Preparing antireflective structures on the surface is also an effective way to improve the surface transmittance.Antireflective structures have good antireflective properties because they reduce the refractive index gap between the air and the interface,which can effectively reduce the surface Fresnel reflection.Femtosecond laser processing is a high-precision method for manufacturing anti-reflective structures,which has the advantages of no material selectivity,high quality(low thermal impact),high precision and flexible processing,making it one of the ideal means for manufacturing micro and nano structures.The main research of this paper is as follows:Anti-reflection properties of zinc sulfide surface microstructures were analyzed by physical modeling with time-domain finite-difference software.Firstly,the FDTD software is used to establish a physical model to analyze the effect of microstructure height variation on anti-reflection properties and to obtain the optimal structure depth.Next,the relationship between taper and transmission performance was explored by varying the width of the bottom slot.The optimal cell structure parameters are determined in conjunction with the actual machining conditions.Finally,onedimensional strip structure arrays and two-dimensional grid structure arrays were modeled to investigate the variation of infrared transmittance with period.The infrared transmittance performance of the two types of structures is compared,and the trend of transmittance with period is investigated using theoretical simulations to provide theoretical guidance for subsequent experimental preparation.Femtosecond laser Bessel beams were used to prepare antireflective microstructures on the Zn S surface to enhance the intrinsic transmission performance,and experiments showed that the transmission rate of both types of microstructure arrays was enhanced in the mid-to far-infrared band of 7-10 μm.Firstly,we introduce the light intensity distribution of Bessel beam and the way to generate Bessel beam by using cone lens and 4f system.Next,the morphology of the two types of structures is characterized and the distribution of elements in the heat-affected zone on the surface is analyzed.Finally,the average transmittance of the prepared 5 μm spaced strip arrays was 78.9% in the 7.5～10 μm band,an improvement of 3.3% relative to the native.The average transmittance of the grid structure with 8 μm spacing is 79.93% in the 8.2～10μm band,an increase of 4.1% relative to the native.It shows that the preparation of strip and grid structures can achieve the purpose of enhancing the surface permeability of zinc sulfide.It is shown that the problem of low transmission performance of zinc sulfide in a wide spectral range can be solved by the present experimental method.A combination of theoretical calculations and laser processing is used to investigate the anti-reflective properties of zinc sulfide surfaces and to illustrate the intrinsic connection between theoretical calculations and practical operations.The antireflective properties of the two types of structures studied in this paper provide new ideas for the subsequent improvement of the surface permeability of zinc sulfide,which has great potential for application in the field of infrared imaging and detection technology. |
