飞秒激光仿生复眼制造进展

Progress in femtosecond laser fabrication of artificial compound eye

复眼系统是自然界中普遍存在的一种视觉成像系统,与单眼相比,它具有体积小、视场角大、景深大以及对快速运动物体灵敏度高等优点.人工仿生的复眼结构在机器人视觉、三维成像、目标跟踪、导航、监测、医学等领域具有极其重要的应用价值.与传统复眼透镜制备技术相比,飞秒激光微纳加工技术在三维制备、高精度加工、可程序化设计等方面具有突出的优势,使得飞秒激光技术成为重要的仿生复眼制备方式.本文总结了飞秒激光加工仿生复眼透镜的最新研究进展,对激光增材和减材两种制备方式分别进行了阐述和分析,对仿生复眼透镜的应用进行了简单的介绍,最后探讨了飞秒激光制备复眼透镜领域存在的一些挑战,并对该领域的未来发展方向进行了展望.

Compound eyes of arthropods are widespread and fascinating visual systems created by natural evolution.Compound eyes consist of many identical small eye units called'ommatidia',each of which is an individual imaging system composed of cornea lens,crystalline cone and rhabdome.Compared with single eyes,compound eyes have distinct advantages in small volumes,large field of view,large depth of field,and high temporal resolution.Therefore,it has sparked considerable research interests in developing various manufacturing technologies towards the fabrication of artificial compound eyes that can be applied in robot vision,three-dimension imaging,motion detection and medical examination.To date,various methods have been proposed for fabricating artificial compound eyes,such as hot embossing method,thermal reflow method,microdroplet jetting method,and ultraprecision machining method.However,these methods inherently suffer from low accuracy and multi-step processing.In particular,it is extremely difficult for these methods to acquire curved artificial compound eye lens,which is quite important for promoting the optical performance and practical applications of artificial compound eyes.In recent years,femtosecond laser direct-writing(FsLDW)has emerged as a practical and promising technique for fabricating artificial compound eyes owing to its capability of three-dimensional(3D)processing and high fabrication precision.First of all,FsLDW is performed by point by point scanning process layer by layer,making it capable of realizing various 3D structures as designed.Second,the extremely high transient intensity of femtosecond laser pulses leads to a non-linear absorption effect(two-photon absorption or multi-photon absorption)with materials in a much smaller volume than the cubic size of wavelength,which endows it with a high resolution(tens of nanometers)beyond the optical diffraction limit.Moreover,the high power of femtosecond laser pulses also provides the ability to process various materials,from soft photopolymer materials to rigid substrates as hard as diamonds.For soft materials,the fabrication mechanism is two-or multi-photon polymerization of photosensitive polymers triggered by the high energy at the localized laser focus region.Through point by point process,two-photon polymerization technology by FsLDW becomes a powerful tool for fabricating complex 3D structures.In spite of this,its shortcoming is obvious as well.The single point scanning procedure causes a relatively low efficiency,which needs further improvement.For hard materials,femtosecond laser serves as an ablation source to form micro-hole,where the local material is removed or chemically modified.Femtosecond laser ablation can be combined with a subsequent etching treatment for improving efficiency,including wet etching and dry etching.The drawback of etching assisted femtosecond laser ablation technology lies in that usually only concave structures can be obtained,further soft embossing treatment is needed in order to acquire convex compound eye lens.In this review,the latest progress in femtosecond laser fabrication of artificial compound eyes is summarized.Manufacturing of artificial compound eyes by FsLDW is introduced according to the two methods mentioned above:femtosecond laser two-photon polymerization that belongs to additive manufacturing and femtosecond laser ablation that is regarded as a subtractive manufacturing method.Then,the diverse applications of artificial compound eyes produced by FsLDW are described.At last,current challenges and future perspectives in this field are discussed.