Micro-nano Structure Fabrication Based On Ultra-fast Bessel Pulse Laser Processing Transparent Material

Ultra-short pulse laser processing can induce various nonlinear effects and efficient energy deposition inside the transparent material for their ultra high peak power intensity and thus they can be used as three-dimensional direct writing tool.And ultra-short pulse laser is also a preferred tool for micro-structure industry based on these advantages.Nevertheless,traditional Gaussian pulse beam is not suitable for processing high-aspect-ratio structures inside the transparent material for their short focusing length and beam size that can not be modified flexibly.Nowadays,Bessel beam has been widely used in precision manufacturing of high-aspect-ratio structures because of the long non-diffraction transmission distance and self-healing.Various material has different physical properties,exploratory parameter experiments therefore be needed in order to find out the optimum range of processing parameters.With this context,in order to manufacture nano-viods structures with high precision and high-aspect-ratio in different transparent dielectrics,detailed experiments have been completed.In this thesis,by correlated experimental results,the mechanism of nano-voids formation and the general rule of laser processing different materials have been discussed.Finally,high quality nano-voids with diameters around hundred nanometers have been manufactured successfully in three different materials,which are fused silica,Gorilla glass and sapphire.The major content of this thesis includes the following sections.Basic theory of the axicon based Gaussian-Bessel beam has been investigated.Tightly focused Bessel beam has been produced using a low angle(1 degree)axicon and a 4f system.An ultra-short Bessel pulse beam processing system has been built based on the theoretically and experimentally analysis.Nano-voids array with large area has been manufactured using non-diffraction Bessel beams and the general rule of laser processing fused silica has been discussed.Experimental results reveal a new mechanism of nano-voids formation which can beexplained as the shock on the surface which is induced by internal material exclusion and inside micro-explosion.Contrast experiment has been used to proved this explanation.Characterization of the embedded high-aspect-ratio nano-void structure is a difficult task.Here an accurate and time-saving tomography-like methodology is proposed and adopted for reconstructing the morphology of high-aspect-ratio nano-holes.The technique allows an accurate assertion of laser parameter and position on nano-structured features.The reconstructed configuration reveals that nanoholes morphologies have a close relationship with energy distribution in the focal region.The minimum size of the nano-void can be 67 nm,and the aspect ratio can be523:1.This new method provided a new thought for embedded high-aspect-ratio nano-structure characterization.In order to promote the industrialization of the ultra-short Bessel processing,a type of commercial aluminosilicate glass named Gorilla glass has been used for nano-void fabrication.Nano-particles and 127 nm diameter high quality nano-void generated on the bottom surface of the sample have been found.Reason of the nano-particle generation can be explained as the difference between the physical properties of fused silica and this commercial aluminosilicate glass(lower annealing point and higher coefficient of thermal expansion).Optimized range of processing parameters can be summarized as 6-10 ps and around 10 ?J/pulse.This will provide valuable experience for Bessel processing Gorilla glass and promote the industrialization of laser processing.C-plane sapphire crystal has also been proceed using ultra-short Bessel pulse beams.Combined with the experience of the commercial aluminosilicate glass processing and the physical properties of sapphire,appropriate laser parameters have been set.Finally,high quality nano-void with 120 nm diameter has been manufactured on sapphire.This work suggests that the physical properties of materials have important influence on the laser processing.