Research On Mechanism And Process Of Nickel Microstructure Fabrication By Femtosecond Laser

As the continuously increasing in demand for the micro-fluidic chip, there is a highertechnological requirement for the metal mold which is used to fabricate the micro-fluidicchip. Nickel is widely used as the metal mold for the micro-fluidic chip as it’s goodcorrosion resistance. Femtosecond laser is becoming the effective and important method forthe fabrication of the micro-structure on the metal as the pulse width is ultra-short and theenergy density is extremely high.This article had explained the mechanism between the femtosecond laser and the metalin detail, then the simulation had been done with the two-temperature model. We found thatthe variations of the coupling time, the equilibrium temperature and the diameter of the holeversus the energy density are very similar, they all tend asymptotically to a constant value asthe energy density increasing. We got the theoretical single pulse ablation threshold basedon the liquid bang theory. Besides, we simulated the influence of the heat-affected zonearound the hole by the energy of the femtosecond laser and we found that the heat-affectedzone decreases asymptotically versus the increase of the energy density. The decrease iscaused mainly by the decrease of the melting and re-solidification zone while the thermalactivation zone unchanged with hundreds of nanometers.Based on the simulation, we do the experiment on the nickel plate with thefemtosecond laser in order to get the ablative hole. First, it’s verified that the nickel plate ismore suitable for the fabrication of the micro-structure than the nickel film. Second, thequality of the micro-structure can be improved by the polishing treatment for the nickelplate and there will be an improvement for the precision of the micro-structure with a morepowerful long-focal length lens. So after the analysis about the experimental result, wefound that the diameter of the hole is increasing almost in linear with the increase of thelaser power while the diameter increases rapidly with the increase of the number of thepulses at the beginning50pulses and then it tends asymptotically to a constant value as thenumber of pulses increasing. For the depth of the hole, we can get the deepest hole use lesspulses with the higher laser power while just higher laser power or more pulses is not benefit for deeper hole. At the same time, the correctness of the theoretical analysis andnumerical simulation are verified by the comparison between the experimental single pulseablation threshold and the theoretical single pulse ablation threshold as well as the diameterof the hole between the experimental and the theoretical.After that we got the ablative line on the nickel plate by the femtosecond laser withseries of laser power and pulses. With shorter distance between the two neighboring holesthe ablative line is more consecutive and the variation of the width of the line versus thelaser power is desired. If the distance is longer the consecutive of the line is worse, but itcan be made up by increasing the laser power. More pulses are benefit for the uniformity ofthe width of the line but it’s not good for the ideal morphology of the ablative line as well ashigher laser power. So we should select the reasonable parameter for fabricating the idealablative line.In a word, we had researched the influence for the size and the morphology of themicro-structure by the laser power, the number of the pulse and the distance between thetwo neighboring holes. It will be the guidance for more complicated micro-structure in thefuture.