Research On Interaction Of Capillary Discharge 46.9nm Laser With Solid Targets

For the last several decades,scientists in the laser field are focusing on the decrease of the wavelength into the shorter domain.The development of the laser source with shorter wavelength promotes the research interest in the interaction of soft X-ray laser with matters.The high energy of the soft X-ray laser photon makes the interaction process essentially different from that with traditional optical lasers.The research on the interaction process of soft X-ray laser with matters is of great significance on micro/nano-processing,micro-characteristic probing and related fields.In this thesis,the interaction process of capillary discharge 46.9nm laser with solid targets was studied theoretically and experimentally.In the theory,thermal effect in the interaction of soft X-ray laser with solid targets was discussed.Because of the high energy photon,the plasma shielding effect could be neglected.Therefore,the Heat Conduction Equation was built with the heat source term.Based on that,the temperature distribution and thermal elastic force of the target induced by the laser irradiation were calculated by COMSOL Multiphysics Software and the thermal effect in the interaction process was analyzed.In the experiment,interaction process of soft X-ray laser with different type materials was researched systematically.With the irradiation of 46.9nm laser,conductor?Cu?,semiconductor?Si?and large bandgap dielectrics?BaF₂,LiF,SiO₂ and fused silica?were damaged.The experimental results were used to analyze the damage mechanism.In terms of theory,heat source function was built in accord with the characteristics of 46.9nm laser.Reflectivity and absorption coefficient were chose based on the type of the materials.On one hand,temperature variation caused by the laser irradiation was simulated on and inside the surface of different targets.According to the calculation,taking the significance of thermal effect in the interaction process into account,the damage results of different materials were discussed.On the basis of the analysis,Cu surface would be melted or even to sputter caused by the laser irradiation.On the other hand,thermal elastic force induced by the laser irradiation was simulated.Based on the calculation and the characteristics of different materials,damage results were analyzed.According to the analysis results,compared with other measured materials,the surface of BaF₂ and LiF would to be smashed by the laser irradiation more easily.In terms of experiment,Ce:YAG scintillator was used to measure the original 46.9nm laser spot systematically.Shape variation of the laser spot with different initial pressure in the capillary and length of the gain medium was studied.Then the focusing methods of 46.9nm laser were studied and selected.The focusing beam path was simulated and the focused spot at different position along the axis was measured.The focused spot of 46.9nm laser was determined by simulation and experimental measurement.The simulated focused spot was in accord with experimental results.After the measurement of the original and focused 46.9nm laser spot,Si,Cu and four large bandgap dielectrics were irradiated by the 46.9nm laser under different experimental environment.Surface responses of different materials under different conditions were recorded.On the surface of Cu,melted trace and nanoparticles induced by the resolidification of liquid copper ejected from the surface were detected.Fragmentation trace on BaF₂ and LiF induced by thermal elastic force was detected and researched.Both the experimental results were in accord with the theoretical expectation.With the use of 46.9nm laser comes the advantage of material surface processing on large bandgap dielectrics.Therefore,in the thesis,the interaction of 46.9nm laser with large bandgap dielectrics was studied deeply.Ablation rate of four dielectrics under different conditions was measured.Laser induced surface periodic micro/nano-structures which was appeared in the damage area steadily on BaF₂ was researched in the experiment.Based on the experimental results,the period of the structures had a relationship with the energy density of the laser,not with the laser pulse number.It increased with the rising of the energy density.The orientation of the structures has a relationship with the cleavage of the crystal,not with the orientation of the 46.9nm laser spot.In terms of theory,according to the calculations,the damage results induced by 46.9nm laser on different materials was predicted,which confirmed the exit of the thermal effect in the interaction process.In terms of experiment,two practical focusing beam paths with respect to 46.9nm laser were built with a toroidal mirror or a SiC spherical mirror.The beam paths were verified to be useful experimentally.To a certain extent,the two beam paths above made up the shortfall of multi-layer spherical mirror,which was used generally in the world.In addition,one method to create periodic micro/nano-structures on BaF₂ surface was explored,which could control the size of the structures.This improves the development of the research on micro/nano-processing on large bandgap dielectrics with a 46.9nm laser,which also promotes the development of capillary discharge soft X-ray laser.