飞秒激光加工蓝宝石超衍射纳米结构

Sub-diffraction-limit fabrication of sapphire by femtosecond laser direct writing

蓝宝石具有超强硬度及耐腐蚀、耐高温、在紫外-红外波段具有良好的透光性等优点,在军工业以及医疗器械方面具有广泛的应用前景.然而这些优点又对蓝宝石的机械加工或化学腐蚀加工带来困难.飞秒激光脉冲具有热损伤小、加工分辨率高、材料选择广等特点,被广泛应用于固体材料改性和高精度三维微纳器件加工.本文提出了利用飞秒激光多光子吸收特性在蓝宝石表面实现超越光学衍射极限的精细加工.利用聚焦后的波长为343 nm的飞秒激光,配合高精密三维压电位移台,实现激光焦点和蓝宝石晶体的相对三维移动,在蓝宝石晶体衬底上进行精确扫描,得到了线宽约61 nm的纳米线,纳米线间的最小间距达到142 nm左右.利用等离子体模型解释了加工得到的纳米条纹的产生原因,研究了激光功率、扫描速度对加工分辨率的影响.最终本工作实现了超越光学衍射极限的加工精度,为实现利用飞秒激光对高硬度材料的微纳结构制备提供了参考.

Sapphire has shown broad application prospects in military and medical fields,due to its high hardness,excellent corrosion resistance and high transmission in the infrared band.However,these characteristics have also brought about lots of difficulties in machining or chemical etching the material.Femtosecond laser processing with excellent characteristics including small heat-affected zones and high processing resolution ratio,has become an emerging field.Therefore,it has important application prospects and has found increasingly wide applications in the fields of material modification and high-quality fabrication of three-dimensional micro-nano structures and devices.In this paper,we propose a method in which femtosecond laser processing based on multi-photon absorption is used to process sapphire beyond the optical diffraction limit.In this work,femtosecond laser with a central wavelength of 343 nm is focused on the sapphire and the surface of sapphire is scanned with the high-precision piezoelectric positioning stages.Nano structures each with a width of about 61 nm are obtained,and the minimum space between the nano structures could be as short as about 142 nm.Further,the influences on the processing resolution from laser power and scanning speed are investigated and the generation mechanism for the nano-ripple structure is discussed.Finally,femtosecond laser processing on the sapphire with a resolution beyond the optical diffraction limit is achieved.This work provides a reference for processing the hard and brittle materials by femtosecond laser.