Research On Patterned Nano-painting Based On Femtosecond Laser

The structural color of materials is produced by the interaction of the micro-scale structures and the light,which provides the unique advantages of being environmentally friendly and never fading.Its rapid development and applications can be attributed to the intensive study of the microscopic morphology of biological surfaces in nature.Currently,structural colors have been widely used in the fields of color printing,new display,high-precision anti-counterfeiting and high-sensitivity sensing.Among the numerous methods of generating structural colors,femtosecond laser-induced periodic surface structures(LIPSS)have shown significant advantages due to the non-polluting,non-contact,and simple fabrication procedures.Usually,the production of LIPSS is based on the tight focusing of the objective lens.However,the micro-scale focusing beam spot area caused by the objective lens seriously limits the efficiency of fabricating the structural-color patterns.In recent years,although a method of the line-focusing by a cylindrical lens has been proved to improve the preparation efficiency of LIPSS,its macro-patterning process still requires a hard mask covered on the material surface,which consequently limits both the spatial accuracy and the quality of the structural colors.In order to solve these common problems,our thesis proposes a new strategy of nano-painting patterns that combines the data slicing of the pattern design,the spatial light modulator to act as virtual dynamic masking,double cylindrical lenses for the linear-shaped focusing and LABVIEW control program.And we have successfully fabricated the single and the composite structural-color patterns on the graphene oxide film,which shows the potential applications in the field of color display,image hiding and anticounterfeiting.The key points of the research are provided as follows:(1)Aiming at the existing problem that the current LIPSS cannot simultaneously guarantee the high quality and the high efficiency during the fabrication of structurecolor patterns,our thesis proposes a novel processing scheme for the LIPSS patterning in the macroscales,which includes the digital slicing of the picture design in the first step,and then utilizing an SLM for modulation of the spatial intensity distribution of the incident laser beam to act as a virtual dynamic mask,and after that two cylindrical lenses for the linear-shaped focal spot scanning to improve the processing efficiency,and a LABVIEW based computer program for the coordinate control of these different parts.Eventually,we have realized the high speed and high efficient preparation of the macro-scale nano-painting patterns.(2)A system and experimental setup for the nanopainting of macro-scale patterns has been established,and it has been successfully applied on several different material surfaces including GO film,metal tungsten and semiconductor Si,which indicates the validity of this method.In particular,the chromatic study of the nanopainted patterns based on r GO-LIPSS shows that the structural colors of the material surface are characterized by the high brightness,high saturation,and high contrast,the performance of which meets or even exceeds the general commercial standards.(3)Based on the measured relationship between the viewing angle and the structural color displaying,we have proposed an experimental approach for the application of anti-counterfeiting by compounding different patterns within the same macroscale surface area but leaving them separate in the microscale.Through varying the directions of the femtosecond laser linear polarization to fabricate different patterns with LIPSS oriented in variable directions,we have preliminarily realized the patterned information hiding and displaying based on the change of the viewing angle.This result indicates the potential in the field of graphic anti-counterfeiting.(4)In order to solve a common problem of the LIPSS-based patterns usually having a small viewing angle range,we have proposed to transform one picture design into multiple identical nanopainting patterns except for their having different structural orientations and then fabricated them separately in the microscale but within the same macroscale surface area.Therefore,the range of viewing angle for the structural colors has been successfully expanded by 3 times,while still maintaining the high spatial resolution of the patterns.