Ultrashort Laser Ablation: Fundamental And Its Application In Fabricating Wedge And Strip Anode

Ultrashort, sub-picosecond lasers bring new opportunities in a variety of technological applications in miro- to nanotechnologies, micro-electronics, measurement and microscopy, medicine industry, biotechnology and aerospace industry. However, the processes governing ultrashort pulsed laser ablation are not completely understood at the moment.In order to fabricate Wedge and Strip Anode(WSA) with high quality, the basic theory of ultrashort laser processing material is analyzed, and the fabrication and testing method of WSA is studied. Regarding on these questions, the main contents, methods and achievements are presented as follows:1. The Galerkin Weighted Residual Method is applied to induce the equivalent integral form of two temperature model(TTM), and the weak forms of TTM are deduced by Green formula, thus the finite element functions of TTM are obtained; The finite element functions of TTM are soluted to study the phase change region during femtosecond laser processing Al film.2. The Drude model and free gas theory are proposed in this work to describe temperature-dependent optical reflectivity and absorption coefficient for laser ablating metal and dielectric materials, and the ultrafast phase change function is incorporated into the TTM to describe the solid to liquid phase change process; An ultrafast thermoelasticity based on TTM is used to study investigate the thermomechanical response of Al film irradiated by picosecond laser by using finite element method(FEM); The electron and lattice temperatures, displacements and stresses are depicted; Results show that the hot-electron blast force can boost the thermoelastic wave induced by picosecond laser.3. A semi-classical two temperature model is studied with finite element calculation method; The spatial and temporal lattice temperature distribution map of Al film irradiated by 0.12 W picosecond laser is depicted; The phase explosion is found to be the reason for ablation; The over-heated zone(OHZ) is defined, and the calculated ablation depths of single pulses coincide with experiment for 10 picosecond lasers.4. The relationship between ablation rate and single pulse laser fluence is studied and the effect of spot overlapping rates on profilograms of grooves is analyzed; The ablation rates calculated from Gaussian Linear method(Gl) are compared with Corrected Gaussian Linear method(CGL), experimental results show that CGL is suitable for calculating ablation rates of grooves; The 3D profilogram of grooves in Al film ablated by 10 ps at different spot overlapping rates are simulated through CGL calculated ablation rates.5. The parameters for picosecond laser ablating insulated grooves of wedge and strip anode(WSA) are studied by theoretical and experimental analysis; Using defocused laser, the WSA is fabricated with high ablation precision and quality; The performances of wedge and strip anode detector with direct collection readout and induction readout methods are studied; The induce charge on every single electrode of WSA is calculated with finite element method; When the radius of charge cloud is 4 mm, the decoding equations and the marginal non-linear performance of fabricated WSA are ascertained.