Ultrafast Laser Multifocus Parallel Processing of Single-Crystalline Diamond
Objective Periodic micro/nanostructures on the surface of diamond can increase transmission,decrease reflection,and improve quantum transport efficiency.Thus,they are suitable for diverse applications in aerospace,biomedicine,integrated photonics devices,and other fields.Conventional processing methods such as electron-beam exposure and ion etching involve many procedures and impose high environmental requirements;moreover,their processing efficiency is subpar.Hence,ultrafast laser micromachining technology has been introduced and has received considerable attention owing to its low thermal effect,high precision,and highly controllable design.However,single-beam ultrafast laser processing,which can process microstructures of specific shapes to a certain extent,can neither achieve fast and efficient fabrication nor satisfy the requirements for industrialization.Therefore,a method that can process periodic microstructures on diamond efficiently and with high quality must be devised.Methods An ultrafast laser-processing system based on a spatial light modulator(SLM)was constructed in-house.Through phase modulation,a Gaussian beam was shaped into 5×5 multifocal beams.The multifocal intensity uniformity generated by the SLM was calculated to be above 92％,which satisfies the requirement for the parallel processing of diamond.The microstructures of the diamond surface were characterized using a scanning electron microscope,and top and side views of the three-dimensional(3D)structure were captured.Additionally,an energy-dispersive spectrometer was employed to analyze the elements of the diamond before and after laser processing.A confocal laser scanning microscope was used to capture the 3D profiles of the diamond surface microstructures.The chemical composition of the diamond before and after laser processing was measured using a Raman spectrometer.Results and Discussions First,a single-focus laser was used to fabricate hemispherical structures on a diamond surface,and the effects of different layer spacings and laser power levels on the surface roughness were investigated.Subsequently,a parallel processing system based on 5×5 multifocal ultrafast laser beams was used to achieve high-precision and high-efficiency machining of 3D periodic structures,such as cylinders,hemispheres,pyramids,and cones,on the surface of a single-crystalline diamond.The fabricated microstructure shows a minimum roughness of 0.16 μm.The top diameter of the pyramid tower is 12.6 μm,the tower height is 101.5 μm,and the top diameter of the cylinders can reach 4.8 μm.Compared with single-beam laser machining,ultrafast laser parallel machining can significantly improve the machining speed while maintaining the machining accuracy.Raman spectra confirmed no significant graphitization or laser heat-affected zones in the laser-processing area,thus indicating no significant changes in the physical property after laser processing.Conclusions In this study,periodic microstructures such as cylinders,hemispheres,pyramids,and cones were successfully fabricated on a diamond surface using the proposed 5×5 ultrafast laser multifocus parallel processing method.For the single microstructure processed,its width,depth,and roughness are 5-100 μm,10-100 μm(with an error within 1.5 μm),and＜0.16 μm,respectively.Elemental analysis and Raman spectroscopy confirmed no carbonization or laser heat-affected zones in the microstructures.Ultrafast laser multifocus parallel processing significantly improves the processing efficiency and precision of diamond and is expected to promote the large-scale use of diamond components with micro/nanostructures in microelectronics,biotechnology,aerospace,and other fields.
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