| Modern infrared detection technology is developing in the direction of diversified application fields and complicated using environments.The infrared window material as the core component should not only have a better transmission effect in the infrared band,but also protect the infrared sensing optoelectronic device from being disturbed and damaged by the external environment.Multilayer antireflection film systems are commonly used in infrared detection applications to increase the infrared transmittance of window materials.However,the film is easy to peel off when heated,with low mechanical strength and poor thermal stability.The antireflection microstructures inspired by moth-eye structures prepared on the surface of the material have the advantages of high mechanical strength,wide spectral bandwidth,wide incident angle.As a new anti-reflection technology,it is widely used in the field of infrared detection.Femtosecond laser processing technology has the advantage of the extremely high instantaneous power,which makes it possible to process any material.At the same time,its high precision,high efficiency,and "cold processing" characteristics are very suitable for the processing of antireflection microstructures.Therefore,this paper will focus on the manufacture of subwavelength antireflection structures.Firstly,the simulation modeling of the array antireflection structure is guided by rigorous coupled-wave analysis.Then build a shaping femtosecond laser processing system,and optimize the laser processing parameters.Finally,the antireflection microstructures were prepared on the surface of zinc sulfide.At the same time,the infrared spectral properties,wettability,mechanical properties,laser damage properties and imaging effects of the antireflection microstructures were detected.The main contents of the paper are as follows:(1)According to the subwavelength diffraction theory,the initial array convex and concave microstructure antireflection model was established,and the electric field distribution of the zinc sulfide surface antireflection structure was calculated by rigorous coupled-wave analysis.Analyze the relationship between the local enhancement of the light field intensity of the antireflection structures and the wavelength of the incident light wave,the incident angle,the height/depth of the anti-reflection structures,and the period of anti-reflection structures.The focus of research is the influence of the changes of parameters such as the profile and size of the antireflection microstructure on the infrared transmission spectrum of zinc sulfide.When the microstructure of the array processed on the surface of zinc sulfide is 3 microns in period and 2.5 microns in height/depth,the maximum transmittance in the infrared band can reach 93%.Through the research,it is concluded that the infrared transmittance of zinc sulfide increases with the increase of the height/depth and the fill factor,and decreases with the increase of the period.These simulation data provide theoretical reference for subsequent experimental research.(2)A method of temporal shaping femtosecond laser processing of antireflection microstructures is proposed.Explore the influence of pulse delay on the structure parameters of the array Gaussian hole,and optimize the laser parameters.The effect of array Gaussian hole structure parameters on the infrared transmittance of Zn S was investigated.When the period of the array Gaussian hole structures prepared by the double-pulse femtosecond laser is 3.5m and the depth is 0.65m,the transmittance of the structures is about 82% near the 9m wavelength,which is higher than 10% in the same band.In addition,an infrared imaging detection system was built to analyze the infrared image data of the array antireflection Gaussian hole structure.Then using it to verify the gain effect of antireflection structure on infrared imaging.(3)Build a spatial shaping femtosecond laser processing system,and using an axicon lens generate a Bessel laser beam with "diffraction-free" properties.According to geometric optics theory,the influence of different axicon tip angles on Bessel beam lasers parameters is calculated and analyzed.The relationship between different Bessel beam lasers and topography of structures is studied by experiments.Array truncated cone antireflection microstructures were prepared on the surface of zinc sulfide by two Bessel beams scanning which is vertical to each other.After experimental detection,it was found that the array truncated cone structures not only improved the transmittance of Zn S in the far-infrared band,but also made it have a wide incidence angle.It also improved the surface hydrophobic properties of Zn S,the contact angle with droplets of water is 170°.(4)Design and build a spatio-temporally shaping femtosecond laser processing system by combining the temporal shaping and spatial shaping technology.Then use it to fabricate an array inverted cone antireflection structures on the surface of Zn S.The influence of the spatial position deviation of the axicon lens on the intensity distribution of the laser beam was calculated by Zemax software.And the evolution relationship of the microstructure topography profile was studied experimentally.Due to the high efficiency of temporal shaping and the deep processing depth of spatial shaping,the spatio-temporally shaping femtosecond laser can complete the fabrication of an array of inverted cone antireflection structures with an area of 100 mm × 100 mm within 80 hours.The array inverted cone structure with a period of 3.5m and a depth of 0.92m not only increases the transmittance of the Zn S to 88%,but also enables it to have a wide spectral bandwidth anti-reflection effect,which further improves the image clarity in the infrared system. |
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