Preparation Of Subwavelength Structure And Its Mechanism Of Laser Induced Damage

With the further development of high power laser technology,the damage resistance and environmental tolerance of optical components are more and more demanding.Because of the subwavelength structure of fused silica surface,the refractive index of the surface can be controlled by micro nano structure,so as to realize various optical properties.On the one hand,the subwavelength structure has broken through the limitation of the material,and can be controlled arbitrarily between the air and the fused silica by the micro nano structure;On the other hand,the application of single material system for fused silica sub wavelength structure in high power laser field has given new meaning.This single material system can effectively avoid the physical and chemical mismatch between the layers under high power laser irradiation,thus greatly enhancing the stability of optical properties of optical components.Under this background,a variety of technical schemes are proposed to prepare a variety of antireflective subwavelength structures,and the anti damage properties of antireflective subwavelength structures are systematically studied.The rigorous vector diffraction theory based on the established analysis model of reducing reflection theory of periodic subwavelength structure;analysis of the structural parameters of subwavelength structures,such as cycle,duty ratio,influence of height on antireflection properties.The results show that the refractive index of subwavelength structure is influenced by the duty cycle,so the parameter has the biggest influence on the efficiency of antireflection.By optimizing,the optimum duty factor is 0.56.With the increase of subwavelength structure,red shift occurs in the anti reflection band.When the period increases gradually,some higher order diffraction components begin to appear in the transmitted light.When the period is much smaller than the wavelength,the period does not affect the anti reflection characteristics of subwavelength structures.The far field through the relationship between the rate and the high order diffraction efficiency and sub wavelength structure cycle analysis,the results show that when the period is less than 200nm,the far-field 351nm wavelength transmittance is approximately equal to the total transmittance,no high order diffraction components transmission components.This shows that the wavelength range of the subwavelength structure for 351nm should be less than 200nm.The characteristics of the light field controlled by the parameters of subwavelength structures are analyzed in detail.The modulation of the subwavelength structure to the light field leads to the distribution of light intensity on the subwavelength structure surface,which can be used in the design of subwavelength structures with high damage threshold.The modulation of the light field under three wavelengths of 355nm,532nm and 1064nm is simulated respectively.The results show that the cycle is the most important parameter affecting the light field regulation,when 0.3 times smaller than the wavelength of the cycle,cycle has little effect on the light field;the same period,part of the air field strength is always greater than the sub wavelength region,with the duty ratio of electric field strength and smaller the air is smaller.The subwavelength structures were prepared based on three kinds of techniques respectively.Preparation of periodic subwavelength structure based on colloidal crystal template method,preparation of random subwavelength structures based on rapid thermal annealing template method and fabrication of random subwavelength structures based on self-mask technique.In the colloidal crystal template preparation of subwavelength structure part,we study the mechanism of self-assembly of two-dimensional colloidal crystal,based on the analysis of the self motion form of microspheres in the assembly process,assembly method of gas-liquid interface improvement,analysis of the gas-liquid interfacial self-assembly process of particle size,concentration and surfactant concentration on the influence law self assembly quality.Under the guidance of this rule,all kinds of high quality and ordered single layer colloidal crystal templates with different sizes were prepared.Periodic subwavelength structures were prepared by one-step and two step methods,respectively.In the one-step method,the influence of the etching time of the plasma on the subwavelength structure was analyzed.Based on the shallow etched sample,the effect of wide spectrum anti reflection and the angle on the ant:ireflection performance of the tapered subwavelength structure prepared by this one-step method are analyzed.The scattering of short wavelength light by subwavelength structure is analyzed by Rayleigh scattering model.In the two step technique,the polystyrene microspheres were reduced by oxygen plasma etching,and then the substrate with controllable morphologies was obtained by etching the substrate with fluorine plasma.Study on the morphology change on polystyrene microspheres trend of oxygen plasma,according to the results of the second chapter is the theoretical simulation design preparation of periodic subwavelength structure,and anti reflection properties of periodic subwavelength structure research.Combining experimental and theoretical analysis,the influence of subwavelength structure height on optical properties is analyzed.The subwavelength structure has excellent anti reflection performance in the range of 300-1400nm,and the highest transmittance of double periodic subwavelength structure is more than 99%.A random subwavelength structure is fabricated by thermal annealing template method.A random Island mask of nanoscale metal was prepared by atmospheric thermal annealing,and then a random subwavelength antireflection structure was fabricated by reactive ion etching.The atmospheric annealing technique mainly controls the random island size and distribution of the surface by annealing temperature and the thickness of the gold nano film with two parameters.The research results show that when the nano Au thin film is lower than 5nm,the mask is too thin and can not effectively protect the substrate,the island shaped mask structure may soon be etched.When the film thickness is more than 10nm,higher annealing temperature and high temperature annealing will cause the surface Island mask size to be uncontrollable.The random subwavelength structure prepared by this technique has excellent antireflective properties in the 400nm-1100nm band,with a maximum transmittance of over 99%.In the fabrication of random subwavelength structures by self mask technique,the formation mechanism of plasma induced self mask was studied.The influence of CHF3 content and etching time on the sub wavelength structure of the fluorocarbon polymer film during the process of producing the grassland effect was analyzed.Combined with the second chapter analysis the theory of optical properties of subwavelength structure analysis,a detailed study of the total reflectance total transmittance,transmittance,reflectance,the relationship between the effect and the analysis of subwavelength structure parameters on the optical properties of the.By optimizing the preparation conditions,the average size of subwavelength structures is as low as 150nm,and the anti reflection characteristics of ultraviolet 351nm are excellent,and the maximum transmittance is above 99%.The prepared subwavelength structures show excellent broadband antireflection properties in the visible range,and the theoretical and experimental results are in good agreement.The maximum sample size is 4 inches.After preparation of subwavelength structure,the damage properties of fused silica substrate and sub wavelength structure after advanced AMP technology were compared and studied.Among them,the fused silica substrate is cleaned to remove oil and impurity defects,and inorganic acid leaching removes metal impurities in the polished and re deposited layer,hydrofluoric acid corrosion,passivation,sub surface scratches.Sub wavelength structure samples were pre washed and inorganic acid leach process.Using fluorescence confocal microscopic imaging technique,Tof-sims element analysis and characterization of the original untreated substrate,and sub wavelength structure of sample surface and sub surface impurity distribution of substrate AMP treatment;analysis of the structural deficiency of three groups of sample surface subsidence by fluorescence spectroscopy;surface weak absorption characterization of three groups of samples using photothermal technique weak absorption.The results showed that AMP substrate and sub wavelength structure surface of the metal impurity content is much lower than that of the original sample,but the deposition of impurities fluorocarbon subwavelength structure sample surface is higher than that of AMP substrate;the preparation process of sub wavelength structure to sample introducing oxygen vacancies,non bridging oxygen and other structural defects.Comparing the weak absorption data,it is found that the average weak absorption level of the subwavelength structure surface is lower than that of the original sample,but higher than that of the AMP substrate.351nm and 532nm laser-induced damage thresholds of three sets of samples were tested.The results show that the damage threshold of 351nm laser induced by subwavelength structure is lower than that of AMP substrate,but higher than that of untreated substrate.The damage threshold of 532nm laser induced by subwavelength structure is higher than that of AMP substrate and untreated substrate.From the introduction of fluorocarbon polymer defects and subwavelength structure light regulation of two angles of the anti damage performance of subwavelength structure 351nm and 532nm different injury,to verify the feasibility of subwavelength structure to improve the components damage threshold.The innovation of this paper is the vector diffraction theory analysis of different sub wavelength structure based on the 351nm,532nm and 1064nm three kinds of wavelength of light field regulation,subwavelength structure design and analysis may have high damage threshold;the preparation process for the first time on the sub wavelength structure system may introduce and damage related defects;by using the technique of fluorescence spectrum analysis,analysis of the distribution of the defects of Tof-Sims technology;photothermal weak absorption to establish the relationship between defects and damage based on;and using the light field regulation damage analysis of subwavelength structure can change;verify the feasibility of subwavelength structure can improve the damage threshold.The first systematic study of the surface of the glass material with fused silica as the representative from the mask forming mechanism of fluorocarbon based on sediment;breakthrough template technology,the preparation of high quality from the ultraviolet to the near infrared wavelength can be arbitrary regulation of the anti reflection structure;at the same time the anti reflection performance of ultra wide spectrum,anti reflection spectrum width is close to 700nm,reached the international advanced level;the sub wavelength structure with excellent anti reflection characteristics were made on the surface of the grating and other non planar structure.