The Basic Study On The Pulsed Laser Ablating Metals

In this thesis, the mechanism of laser ablating copper material is studied by the interaction of different duration pulse lasers and the copper-targets. The expanding mechanism and expanding velocity of the particles ablated by a nanosecond (ns) pulse laser from the material surface is analyzed and measured by the electrostatic Langmuir probe method. The ablated depth on the copper surface by the ns pulse laser with different pulse energy and surroundings pressure is measured by using a three-dimensions surface profiler. The competition between the thermal-equilibrium ablation and the non-equilibrium electrostatic field ablation in the process of 1-20 picoseconds (ps) pulse laser etching copper-target is discussed based on the numerical simulation. A brief statement on the mechanism of the femtosecond pulse laser ablating state materials is presented for the integrality of this thesis. The conclusions obtained are summarized as follows:1. When the pulse duration is less than 100fs in the process of laser etching metals, the heat conduction effect can be ignored because its relaxation time scale is much longer than the interaction duration. The ejective electrons from the target surface are accelerated by the laser field and a strong electrostatic field (non-equilibrium) is instantaneously formed due to the separation of the positive and negative charge centers. When the electrostatic field is strong enough, the negative charge center pulls the ions directly out of the copper-target surface by the laser field accelerating the ejective electrons further, by which the etching process is actualized.2. Due to the interaction duration of the laser-metal, the process of 1-20ps pulses ablating the metal-targets becomes extremely complicated because both the mechanisms, thermal-equilibrium ablation and non-equilibrium electrostatic field ablation, are can not neglected in the competition. But for the shorter duration pulse the non-equilibrium electrostatic field ablation is dominant, and vice versa.3. The process of thermal-equilibrium ablation is dominant in the ns pulse laser etching copper-target. The experiment results show that, the etching process is changed from the normal evaporation to the liquid-phase exploding along with the pulse energy increase; the surroundings pressure also affects the plasma expanding greatly. We find that the ablated particles assemble on the target surface and absorb lots of the incident pulse energy, which process makes against the effectively ablation; the heat-effect zone exists obviously in the ns pulse etching process, which reduces not only the processing efficiency but also the ablation quality and precision.