Heat Accumulation In High Repetition Rate Femtosecond Laser Micromachining And Its Applications

Femtosecond laser micromachining has gained wide applications in many areas,but the tr aditional la ser s ource f or mic romachining was low r epetition ratefemtosecond l aser, w hich l imited t he m achining efficiency a nd s peed. A highrepetition rate femtosecond laser can solve this problem very well. However, whenthe laser pulse repetition rate is increased, the heat accumulation between laser pulseswill be more and more notable, which will bring up the heat effects.This t hesis focuses on heat accumulation in high r epetition rate femtosecondlaser micromachining and its applications based on a high repetition rate photoniccrystal fiber femtosecond laser.The contents are listed below:1. The research progress of high repetition femtosecond laser micromachiningand the general theory about femtosecond laser micromachining was presented.2. The m icromachining pr ocess of m etal and transparent di electric w asnumerically modeled using two-temperature equation under3D cylindrical coordinateand the avalanche ionization model respectively, from which it was deduced that thelaser pulse energy used in our experiments was below the single pulse threshold. Thenthe te mperature di stribution of me tal f ilm a nd tr ansparent di electric under hi ghrepetition rate femtosecond laser was analyzed using reduced1D heat transfer modelin Cartesian coordinate system and spherical coordinate, respectively. The influenceof r epetition r ate on f emtosecond l aser m icromachining w as also r esearchednumerically.3. The experiment system and laser machining method was introduced, includinglaser f ocus pos ition de termination, i mage de tection, l aser s pot a nd t hresholdmeasurement.4. T he a pplication of h eat a ccumulation f or hi gh r epetition rate f emtosecondlaser in metal micromachining was researched.(1) Some micro-reliefs were createdon bulk metal surface. The influence of laser parameters under different repetition ratewas researched and the mechanism for micro-reliefs was given.(2) Uniform nanoparticles were produced on Copper film surface. The influence of laser parameters onthe nano particle shape and size was researched and the mechanism was developed.(3) The i nfluence o f l aser r epetition rate on metal m achining w as experimentallyinvestigated.5. T he a pplication of h eat a ccumulation f or hi gh r epetition r ate f emtosecondlaser in transparent dielectric micromachining was researched. Optical waveguide andphotonic crystal waveguide structure was created inside fused silica using52MHzand650kHz femtosecond laser respectively. The influence of laser parameters onwaveguide formation and the mechanism was analyzed. The laser transmittance modethrough t he w aveguide was i nspected a nd t he change o f i ndex of r efraction wasmeasured.6. T he s urface da mage t hreshold of G aP w as m easured b y area r egressionmethod, and the influence of laser repetition rate on s emiconductor machining wasexperimentally studied.