| The study of the periodic structure on the material surface induced by pulsed laser is always a hot issue. Recently, the periodic structure of the metal surface made of femtosecond laser have extensive applications in many fields. It can be used to modify the surface properties of the metal surface. Such as increasing the surface optical absorption, emission rate or enhanced biological compatibility,etc. The functional properties of these metals have important applications in the fields of energy, military and medicine.In this thesis, we focus on the surface of metal titanium surface by focusing femtosecond laser directly, and we study the microstructure of the micro nanostructure in two ways: single pulse cumulative irradiation and double pulse(pulse delay in picosecond order). The experimental results show that the structure of the sub wavelength fringes of the titanium sample surface can be covered by the femtosecond laser, which has a close relationship with the laser energy density, pulse number and pulse delay. In particular, by optimizing the delay time between two femtosecond optical pulses, especially the fringe edges is more clearly when pulse delay is more than 5ps, the fringe(period is about 500nm)structure of the titanium surface can be improved obviously, which is found to be important for the optimization of the surface morphology. At the same time, it can be found that the microstructure coverage area of the surface will change with the increase of the time delay,that is, the area of the micro structure is gradually reduced with the increase of time delay. By using the double temperature equation numerical simulation, the ultrafast thermodynamic process of the electrons and the lattice in the process of the double pulse is studied. On the other hand, this paper also carried out the the study on the metal aluminum by the double pulse femtosecond laser. It was found that the formation of stripe clarity of aluminum is lower than that of titanium. |
PDF Full Text Request