Surface Micromachining With Femtosecond Laser Pulses

As ultrashort pulse duration confines heat diffusion, the femtosecond laser pulses provide a promising tool for the alteration of surface morphology and texture without significant damage to the underlying material. Unique materials modification and surface texturing effects may be achieved through the controlled use of laser irradiation parameters. In this thesis, surface micromaching with femtosecond laser pulses was studied. The main points are classified as follows:1. Detailed studies on the micromachining of silicon. The effects of debris on the micromachining precision were studied. We try to deposite thin film for reducing debris on silicon surface before laser micromaching, and the effect of reducing debris was investigated.2. Detailed studies on the ablation of amorphous alloy FeCuNbSiB in air with femtosecond laser. The accumulation effect of multiple pulses and formation law of periodical ripples were discovered. The result indicates that the physical mechanisms responsible for material removal during ablation transfer from equilibrium vaporization to phase explosion and some liquid flow occurred as laser power increasing. As observed with X-ray diffraction (XRD) and Field Emission Transmission Electron Microscopy (FETEM), the amorphous form is kept with no change in the damaged zone, and there is few crystallization form in ablation zone. So femtosecond laser is very suitable to cut amorphous alloy.3. Detailed studies on the ablation of Ni foil.The results show that the phase explosion occurred and rapid expulsion of large amount of liquid and vapor droplets which cooled quickly and resolidified. The observed morphologies seem to suggest that phase explosion and extremely high cooling rate are the most probable physical mechanisms responsible for the formation of surface nanostructures. The two temperature model (TTM) calculation and Field Emission Transmission Electron Microscopy (FETEM) were used to study the nature of the morphology and grain structure of nickel foil, and determine the essential features .The results indicate that there are many random nanostructures in the centre of the ablated region composed of nanocrystalline grains as well as some core-shell structures, and no amorphous was observed.