| Transparent brittle materials such as sapphire,glass,and ceramics have great potential for applications in related fields such as consumer electronics,display,illumination,aerospace,defense,and medicine.In these applications,high quality and high precision processing of materials is required,and traditional point-by-point processing is inefficient,while the spot focused inside the material can bring about severe aberrations.By precisely modulating the light field distribution inside the material,the processing efficiency,processing accuracy,and energy utilization can be improved at the same time,therefore it is important for the application in hard-brittle materials.In this dissertation,we proposed the light-field modulation algorithms for the internal processing of transparent materials,and developed the corresponding optical systems for long-depth-of-focus cutting of glass,stealth dicing of silicon wafers and glass,and three-dimensional marking inside materials.Finally,we performed micro-nano processing experiments.The main research works in the dissertation are as follows:(1)An on-axis energy-controllable long-depth-of-focus beam optical system was developed to realize long-depth-of-focus cutting of transparent thick-plate materials.Firstly,the correspondence between radial and axial coordinates is determined,and the phase derivative of the objective lens is solved.Thus,the depth-of-focus position,length,direction,and energy distribution of the on-axis light intensity distribution are controllable respectively.According to the above algorithm,a long depth-of-focus cutting optical system based on a liquid crystal spatial light modulator was constructed and the laser cutting experiments were performed on different thicknesses of glass.Cuttings of glass plates with 300 μm thickness and 800 μm thickness are accomplished in a single scan respectively using long depth-of-focus beams of 500 μm and 1000 μm.Compared with the conventional long-depth-of-focus method,the depth-of-focus position,length,direction,and energy distribution can be flexibly adjusted with the proposed algorithm.(2)An on-axis multifocal optical system with the controllable number,energy,and interval of focal points is designed and applied to the stealth dicing of silicon wafers.Firstly,an on-axis multifocal model with a large numerical aperture objective is established,and the on-axis optical field modulation problem is converted into a phase retrieval problem with a one-dimensional function by adjusting the unit defocusing distance and the coefficients of the Fourier expansion,and the on-axis focal number,focal interval,and focal energy are simultaneously controllable.By applying the bias compensation method,the numerical solution is optimized,and the two-dimensional phase plane is derived by nonlinear point-topoint mapping.A multi-focus stealth dicing optical system based on a liquid crystal spatial light modulator for silicon wafers is built.Using a 1342 nm wavelength nanosecond laser,a 250 μm thick wafer is stealth diced with four single-focus scans,two dual-focus scans,and one triple-focus scan,respectively.Compared with the conventional single-focus stealth dicing method,the number of scans is reduced and the cutting efficiency is improved significantly.(3)A multifocal spherical aberration compensation algorithm inside the material is proposed for application in the stealth dicing of thick glass plates.In this algorithm,the spherical aberration compensation phase and defocusing phase inside the material are obtained by analyzing the aberration caused by the material boundary.Subsequently,we transform the multi-focusing modulation problem inside the material into a phase retrieval problem as a onedimensional function.The extent of the spherical aberration is reflected in the experiment by measuring the width of the heat-affected zone,which gradually increases from 89.2 μm to 196.0 μm during the depth increases from 0.5 mm to 3.5 mm before aberration compensation is performed.After aberration compensation,the heat-affected zone increases from 37.9 μm to 52.3 μm,which is a small increase.Single-focus,bifocus,and trifocus stealth dicing experiments were performed on 1 mm-thick glass,using an infrared solid-state laser at 1064 nm,and six equally spaced scratches were scanned inside the material.After compensating the spherical aberration,a more concentrated energy distribution can be obtained,improving the cutting efficiency and cutting quality.(4)A spherical compensation compensated 3D multifocal algorithm is investigated to achieve 3D parallel marking inside the material.In the iterative optimization process,the effects brought by the processing depth,the refractive index of the material,and the numerical aperture of the objective lens are considered.In the phase retrieval process,the optical field distribution inside the material is obtained by adjusting the Ewald cap radius and increasing the spherical aberration function.By introducing the weighting factor,the focal uniformity was improved from 81.3% to more than 95.0%.By adjusting the number of axial samples,the focus uniformity was improved from 85.9% to 99.7%.Based on the above algorithm,a multifocal parallel marking system was built.Three-dimensional parallel marking experiments were performed within 300 μm and at 1 mm depth inside the material using 0.55 and 0.67 numerical aperture objectives,respectively.By switching the loaded phase holograms,linear,planar,and volumetric intensity distributions were achieved respectively,while higher processing accuracy could be realized after compensating for aberrations.This method enables efficient and high-quality parallel marking of arbitrary 3D structures inside the material.In summary,this dissertation improves the efficiency,quality and energy utilization of laser cutting and marking by modulating the three-dimensional laser field focused inside the transparent brittle materials,providing a novel technical approach for laser micro-nano processing. |
