Research On Processing Of Silica Fiber Ceramic Based On The Femtosecond Laser

Silica fiber ceramic which is a new kind of superhard composite material has a wide range of applications both in the military and civilian industries due of its unparalleled advantages. The research on processing of the material is of great significance, for there is still no systematic research work at home and abroad. The high hardness and strength characteristics of silica fiber make it difficult to be processed by traditional machining methods, and those methods meet serious aging problem and cannot meet the accuracy requirements. To solve the problems above, the research on processing technology and mechanism of silica fiber applying femtosecond laser was carried out in this paper based on the distinct advantages of femtosecond laser microprocessing.In this paper, all experiments were done using femtosecond write-processing methods of femtosecond laser micromachining system. The femtosecond laser damage thresholds of silica fiber and sapphire were measured using extrapolation, and the relationship between ablation threshold and lattice structure was obtained by comparing the thresholds of silica fiber and sapphire. The results showed the stronger atoms bound together, the higher energy damaging this material requires. At the same time the dependence of the ablation threshold energy density with the number of pulses was researched, which showed that there’s incubation effect in the event of multi-shot. When a piece of material is exposed to laser radiation whose energy density is below the threshold, the material is modified rather than macroscopically damaged, so removal of material also occurs although the subsequent laser pulse energy is less than the ablation threshold of single pulse. The reason why incubation effect plays a hole in silica fiber is the presence of impurities, and color centers are formed under laser irradiation in sapphire.Optical microscope and surface profiler were used to analyze the relationship between parameters and processing effect, and micro-machining parameters were optimized. The results showed that the morphology is better but the removal rate of single pulse is smaller and base angle is bigger when the direction of processing is perpendicular to the fiber. The removal rate of material and the heat affected zone increase with the growth of laser energy. With the increase of processing times, the depths of grooves increase rapidly at the beginning and tend to be unchanged at last, but widths of grooves vary little. The depths of grooves are inversely correlated with processing speed and the widths vary little with the processing speed under the experimental conditions. When the laser is circularly polarized light, machining morphology and material removal rate are unaffected by the direction of movement, the material removal rate and surface morphology are different at different movement directions when the laser is linearly polarized light. The laser of low repetition rate shows small heat-affected zone and poor processing edge quality.Finally laser induced plasma emission lines were collected during the experiment and the element valences of plasma emission lines during femtosecond and nanosecond lasers were compared, and then the mechanism of the processing of silica fiber applying femtosecond laser was analyzed and charge transfer process during femtosecond laser processing was acquired. We found that the bonding electrons of the wide band gap superhard material were excited by multiphoton absorption under femtosecond laser irradiation, so that the covalent bond was broken. After electronic dephasing process and electronic thermalization process, laser energy deposited into the material’s surface layer of a few nanometers thickness rapidly, so the temperature of electrons reached far beyond vaporization temperature, and then the material was removed following the plasma jet, thus achieving the non-thermal processing.