Femtosecond Laser Fabrication For Functional Micro/nano Devices In Sapphire

Sapphire has been widely used in the fields of aerospace,defense,medical,and semiconductors owing to its high transmittance in wide spectrum,high hardness,and chemical stability.Owing to the lack of effective machining technology,the work on micro/nano functional devices on sapphire has been developing slowly.For instance,it is difficult to fabricate micro/nano devices using conventional machining process,and chemical etching can only fabricate two-dimensional(2D)structures on flat substrates.Femtosecond laser(fs-laser)fabricating technology has become common for fabricating functional micro/nano devices in transparent materials owing to its high precision,three-dimensional(3D)machining capability,and processing of various materials.However,as an important transparent material,the work of fs-laser fabricating sapphire is still in the mechanism research stage.Although there have been a few reports of functional micro/nano devices on sapphire fabricated through laser-induced modification and wet etching assisted fs-laser fabrication,the variety of devices is small.Through analysis,the main reason for this phenomenon is that it is difficult to control the degree of laser-induced modification,resulting in generating cracks due to the stress accumulation and causing low fidelity of the devices fabricated by fs-laser fabricating technology,which affects the precision of this technology and the controllable fabrication of complex 3D devices.Based on the requirements of high-quality functional micro/nano devices on sapphire,owing to the existing problems and challenges of fs-laser fabricating technology,fs-laser in-situ self-annealing technology was innovatively proposed to solve the problem of cracking in laser scanning.Therefore,various high-quality embedded micro-optical devices in sapphire were fabricated.To expand the application field of the devices fabricated by fs-laser fabricating technology,the difference of the etching rate between laser modified region and unmodified region was improved by controlling the degree of laser-induced modification,enhancing the fidelity of the process.Therefore,many high-quality functional micro/nano devices in sapphire were fabricated.The specific research results are as follows:1.Fs-laser in-situ self-annealing technology inhibits the generation and propagation of cracks.The fs-laser in-situ self-annealing technology was innovatively proposed.Experimental results indicate that the fs-laser with a high repetition rate inhibits the generation and propagation of cracks.The mechanism of the technology is as follows:(1)fs-laser with a high repetition rate induces recrystallization,reducing the stress generated by laser modification;(2)fs-laser with a high repetition rate forms self-organizing nano-fringe,which reduces the void size of a laser-scanned structure;(3)the artificial introduction of fs-laser inducing nano-grating perpendicular to the direction of crack propagation realizes the "stitching" of crack,reducing the probability of crack propagation.It has been proved that the fs-laser in-situ self-annealing technology significantly relieves the stress and increases the crack generation threshold of sapphire scanned by fs-laser to 2.7 times,which promotes the development of high-quality functional micro/nano devices in sapphire by fs-laser fabricating technology.2.Fabrication of high-quality embedded micro-optical devices in sapphire by fs-laser modification.Fs-laser in-situ self-annealing technology reduces the stress,inhibiting the microcracks in the fabrication of embedded devices and avoiding the cracking phenomenon caused by increasing the thickness of the device to meet the phase modulation.Based on these two optimizations,various high-quality embedded micro-optical devices were fabricated in sapphire,including a 2D geometric phase lens with stable focusing characteristics at 800?;a large-size multilayer quarter-wave plate with 94.5% efficiency;3D continuous-surface spiral zone plates for generating high-quality vortex beam;large internal patterned structures for optical encryption,optical storage and beam shaping.The components fabricated by this method have the characteristics of good morphology,high efficiency,and stable optical properties in different environments,having broad application prospects.3.Fabrication of high-quality functional micro/nano devices in sapphire by wet etching assisted fs-laser fabricating technology.The difference in the etching rate between the laser-modified region and unmodified region is improved by controlling the degree of laser modification,improving the precision and fidelity of the fabricated devices.High-quality microchannels inside sapphire were fabricated using wet etching assisted fs-laser fabricating technology with a maximum aspect ratio of 110000:1,maximum etching length of 3.5 cm,and minimum etching linewidth of 12 nm.Because the roughness of the sidewall of the microchannel is 26 nm,which ensures smooth water flow,the device can be used for water-cooling,and the cooling range reaches 70?.On this basis,the bandgap of the 3D photonic crystal fabricated by this method in sapphire could be modulated by injecting different liquids.Moreover,many 3D micro/nano devices with controllable morphology were fabricated using this technology on sapphire and the fabricating efficiency was increased up to 200 times.Finally,we extend this technique to the field of fs-laser drilling,and we realize the microhole and microhole array of arbitrary size,arbitrary taper,and arbitrary shape in transparent materials.These works provide a simple and universal fabricating scheme for high-quality functional devices applied in microfluidic,optofluidic,and micro-optics.In conclusion,to fabricate high-quality functional micro/nano devices in sapphire,the fs-laser in-situ self-annealing technology was proposed to suppress the generation and propagation of cracks.Various high-quality embedded micro-optical elements in sapphire were fabricated through fs-laser modification.Moreover,the precision and fidelity of the devices fabricated by wet etching assisted fs-laser fabricating technology were improved by controlling the degree of fs-laser induced modification,realizing various high-quality functional micro/nano devices in sapphire.The above work proposes a novel method for fabricating functional integrated chips in transparent materials for defense,aerospace,civil medical,and other fields.Additionally,it provides a key technology for high precision removal of hard and brittle materials in MEMS device manufacturing and 3D electronic integration.