Research On Data Model Of Femto-second Laser Micro-nano-fabrication

Femtosecond laser micro-nano-fabrication technology (FsLF) is a simple, high accuracy and three dimensional (3D) fabrication technology. When applied to fabrication, this technology requires a data model that is set up for the object to create. It is the most important part of the FsLF process to build a appropriate data model. The data model represents the structure of the object and the detailed scanning mode. For more complexed objects, it is essential to build more complex model and optimized scanning mode to assure the high precision of the fabrication. However, so far, there is not any software developed for generating data model for FsLF technology. In this thesis, the data models used in FsLF are generated optimized based on CAD technology and analytical equations which complement each other. We have solved some key problems that emerge in the generating process of complex data model which have been applied in the femtosecond laser direct writing of high-quality micro-nano structures. For instance, in the transformation of STL file, we have achieved some innovative results, which offers a new strategy of data processing for the field of rapid prototyping. Finally, we combine computer simulation and experiments to design several high-precision micro-optical elements and study their optical performance systematically. In addition, exploratory researches on application of femtosecond laser micro-nano-fabrication tachnology in integrated optics are also conducted. Main contents of the thesis are shown as follows:Firstly, The system driver software is the key part of the fabrication process.n Control precision and motion range are two important parameters of a femtosecond laser micro-nano-fabrication system. Optimization was made on the FsLF system driver software as well as the high-precision positioning of micro-nano-fabrication based on an objective lens, a digital scanning galvanometer and a linear motor drive flotation platform. Further, the optimization of the above parameters are cooperated with buffer mode and PSO system to enhance the smoothness.(1) The surface quality is very important for high-precision micro-nao fabracation, especially for high quality micro optical devices. High precision optical elements require low surface roughness, which requires a high control precision of the fabrication system, that is, high precision spatial location and high precision of exposure time control. To reduce the roughness of the target, we must improve the resolution of the processing through optimizing the control program of the scanning system which cooperating the digital driving galvanometer with the objective lens. In this thesis, buffer mode in processing can reduce the exposure time to microseconds and reduce resolution to less than 20 nm and average surface roughness to less than 2.5 nm. The diffraction efficiency of zone plate fabricated in buffer mode processing reached 35.8% while that of zone plate fabricated in no buffer mode processing is 30% that is an obvious increasement.(2)The digital driving galvanometer cooperating with objective lens system has a relative small range about 100μm which limits the application of fFsLF.To enhance the fabrication range of FsLF system, we utilize a air-bearing stage driven by a line motor. However, due to the high inertia of the stage, the enhancement of fabrication range is at the cost of reduction of capability of fabricating complex objects. In order to eliminate this paradox, we use multi-threaded control mode with PSO (Position Synchronized Output) system. In addition, the dynamic velocity control system is also designed to optimize the fabrication process. The PSO system combined with the dynamic velocity control system can enhance the ability of fabricating complex structures which can be exemplified by the smoothness and completeness of the heart model fabricated by the system. So the optimized large-range fabrication system could be applied into the area of microfluidics and MEMS furtherly.Secondly, with the design of the above system of FsLF, we can use data model for processing. We have made a series of researches on generating the data model Of STL files and analytical equation mainly, and the two ways to achieve data model were optimized. We realize fabrication of high-smoothness cambered micro-lens and some other complex 3D structures in practice.(1) A Cartesian coordinate system makes a great enhacement of transfomation efficiency when using this algorithm to respair data instead of STL mode. Detecting the intersection ring through the interacted algorithm b the platform and STL model. We utilize the method of intersecting line with intersection ring to realize the transformation from STL data mode to point cloud of entity data. The algorithm based on STL date model transformation is raised first in this thesis. The curvature degree is designed dynamically to control the cutting density which could be benefit for keeping the STL data model perfect and avoiding the leaking hole in the bipolar. Innovatively, the end-on normal vector is caculated through the normal vector of the plane including the end-on dots to scale the STL data model.(2) When fabricating some cambered structures, the rough edges and corners are harmful for the high precision fabrication of micro-devices. We raised a new scanning mode that is equal-radian incision scanning mode, in other words, the distance between the adjacent dots along the cambered surface is constant and the height is variable. Through the optimization in this method, high-quality diamond crystal structure, high stuffed array of aspheric surface micro-lens and biomimetic compound eye structure were all fabricated with ideal optical properties. Especially, the visual angle of biomimetic compound eye could attain 90°which exceseded the 10°largely.Thirdly, through the optimization of control software and data model, as a high-resolution processing method, the FsLF technology has a certain advantage in the production of various high-quality microstrictures and micro-optical elements. In this thesis, several micro-optical elements such as array of zone plates and high-precision microlens were produced and studied.(1) The Fresnel zone plates are important optical devices. However, the diffraction efficiency of normal optical element is low. Herein, the efficiency can be improved by increasing the number of levels of the optical element. To enhance diffraction efficiency of Fresnel zone plates, we designed and produced the eight-level Fresnel zone plate, whose diffraction efficiency reached at least 85%. We used the created Fresnel zone plates for laser collimation. The divergent angle of the laser was reduced from 20 milliradians to less than 10 milliradians.(2) Except single zone plate, we designed and produced zone plates array and tested its optical performance. We used photoelectric conversion device to measure the diffraction efficiency of Fresnel zone plates. Under irradiation with a wavelength of 532 nm, we measured the diffraction efficiency of the square-, hexagon-, and 100%-fill-factor lenslet arrays, and the results are 33.7%,35% and 33%, respectively. The diffraction efficiency of hexagon-lenslet array of Fresnel zone plates is very close to the theoretical value 40.5%. To improve the efficiency of utilization of light energy of zone plate array, we designed and produced square-, hexagon-, and 100% fill factor arrays of eight-level zone plates and attain excellent optical performance.(3) In this thesis, hyperboloid formula with certain conditions was deduced to meet fabrication of strong focusing lenses, and was proved that which should be adopted relies on the specific case of the refractive index of a lens. Spherical and hyperbolic lenses were fabricated and the focusing efficiency of a hyperbolic micro-lens is 50% higher than that of a spherical lens.