Research On Functional Structures And Characterization Of Surface Prepared By Ultrashort Pulsed Laser Micro-nano Processing

In recent decades,the birth and rapid development of ultrashort pulsed laser systems have contributed to the development and maturity of various research works in the field of precision micro-nano processing of materials.And rich results have been achieved.The continuous development of material surface functionalization technology puts forward more stringent requirements on the precision,efficiency and scope of application of the preparation technology.Compared with chemical etching,coating,reactive ion etching and other methods,Femtosecond laser micromachining technology,as a new micro-nano structure preparation technology,breaks the limitation of traditional machining methods on types and sizes of material.With its remarkable advantages such as contactless machining and diversity of machining morphology,femtosecond laser micromachining technology has developed into an irreplaceable new method for preparing surface micro-nano structures.The technology of preparing surface functional micro-nano structures based on ultrafast laser provides a new way to change or enhance the surface functional characteristics of materials,and has been applied to industrial processing in recent years.In this paper,the author takes the advantage of ultrafast laser technology to control the surface functional properties of materials,and focuses on the study of the optical properties and wettability of solid materials under the direct writing mode of femtosecond laser.At the same time,the author is committed to exploring the solid material surface micro-nano structure forming mechanism and the material change process,propeling the ultrashort pulse laser micro-nano structure of industrial application.The main work and innovations achieved are as follows:1)In order to solve the problem of rapid preparation of anti-reflective function surface of titanium alloy,a two-step strategy of using nanosecond laser and femtosecond laser to construct the anti-reflective surface of TC4 titanium alloy is proposed.Firstly,the micron-scale array structure can be rapidly formed on the titanium alloy surface by taking the advantage of high processing efficiency of nanosecond laser.At the same time,the densely arranged micro-scale air holes formed on the titanium alloy surface have been systematically studied,and it has been preliminarily confirmed that these holes play a major role in anti-reflection by forming multiple reflections of incident light.Subsequently,the nanostructure on the air hole wall was induced by femtosecond laser,and the micro-nano layered composite structure was successfully prepared on the titanium alloy surface,which further enhanced the overall anti-reflection characteristics of the surface structure and achieved satisfactory anti-reflection effect.In the wavelength of 250 nm-2250 nm,the surface reflectance of the samples covered by the two-scale structure is less than 4.7%.This two-step strategy that makes full use of the advantages of nanosecond laser and femtosecond laser processing is an efficient choice for constructing functional surfaces.2)In order to achieve the research goal of long-term efficient anti-reflection micro and nano structures on copper surface,it is proposed that the high power density property of femtosecond pulses is used to build up rich micro and nano composite structures on copper surface to achieve the efficient anti-reflection functional properties of copper surface.At the same time,by using magnetron sputtering to increase the plating of SiO2 protective film,the long-term effective isolation of the micro-nano structure on the copper surface from the environment can prevent it from chemically reacting with oxygen in the air.In addition,the author explores the diffuse reflection characteristics of the micro-nano structure on the surface of uncoated copper and the SiO2 protective film under wide spectrum,and proves that the SiO₂ protective film will not affect the anti-reflection function of the micro-nano structure on the surface of copper induced by laser.The average reflectivity of the two copper surfaces is 7.4%in the wavelength from 250 nm to 2250 nm.The average reflectivity of the micro-nano structure on the uncoated copper surface increased to 12%after the two copper surface structures were left standing in air for 60 days,while the average reflectivity of the micro-nano structure on the copper surface with SiO2 protective film remained at 7.4%.The change of element content before and after coating was obtained by energy dispersive X-ray spectroscopy,which confirmed that SiO2 protective film was adhered on the surface of the material.This work provides a solution to promote the fabrication of long-term efficient anti-reflection micro-nano structures on copper surfaces.3)In this paper,we designed and built a micro-nano structure processing system of ultrashort pulse laser surface with the function of online monitoring,and explored the response characteristics of high thermal conductivity graphite surface under the action of ultrashort pulse laser.At the same time,the influence of laser scanning spacing and pulse space deposition density on the surface modification mechanism and characteristics of high thermal conductivity graphite were discussed.Experiments verify the rapid preparation scheme of dual-function anti-reflection surface with superhydrophilic characteristics based on femtosecond laser writing.By this method,the graphite surface can be quickly covered with abundant micro-nano structures.In addition,the formation mechanism of micro nanostructures is explored,which is attributed to the ablation of multi pulse femtosecond laser and surface plasmon absorption.Also,the dependence of the broad-spectrum reflectance of the graphite surface on the scan interval and pulse energy was carefully investigated.In the ultraviolet-visible-near-infrared（250 nm-2250 nm）,the average diffuse reflectance of the graphite surface structure obtained by this scheme is less than 2.7%.At the same time,under three different temperature environments including room temperature,high temperature and low temperature,it has excellent superhydrophilicity on the wide spectrum antireflection surface.Graphite oxide/graphene was formed on the surface of bifunctional graphite by Raman spectroscopy and X-ray energy dispersive spectroscopy.Femtosecond laser direct writing method has the characteristics of high processing efficiency,high controllability,environmental friendly and pollution-free.At the same time,it demonstrates the potential application of femtosecond laser direct writing strategy in the preparation of interfacial functional sensors.