| Abstract [eng] |
In a competitive industry, efficiency of material processing must constantly increase, so various methods to achieve that are being sought. A burst mode, which generates pulses that are divided into high-repetition frequency sub pulses, was invented as one of the ways to increase processing efficiency. The resulting ablation efficiencies of the burst mode vary for different materials, so it is not yet easy to predict what parameters are required for the material being processed. In order to increase material processing efficiency, it is important to get acquainted with the trends of damage dynamics using different processing configurations. In this paper, the effect of pulse interaction on crystalline unalloyed silicon using pump-probing method is investigated. The study used a Yb:KGW laser system emitting 1030 nm, 320 fs wavelength radiation, which beam was used to excite the sample, and a second harmonic was generated to probe the sample at 515 nm. To verify that the system was functioning properly, the dynamics of single-pulse-induced damage in chrome was first recorded. In the dynamics, metal-specific changes in the reflection coefficient were observed and recorded at different delay times. After making sure that the system was suitable for recording the dynamics, other experiments were performed with silicon. No ablation was observed when silicon was excited by single pulses with energy densities of 0,74 J/cm2 and 0,55 J/cm2, but the processes like changing density of excited carriers, temperature rise, overheating and cooling of the melt can be observed with the help of dynamics. In the final state, the formation of an amorphous silicon ring with a higher coefficient of reflection was observed. The same experiments were performed with double excitation pulses, which were delayed with respect to each other by durations: 1 ps, 300 ps, 600 ps. The observed dynamics show that the same processes are observed during single pulse and double pulse processing with a 1 ps delay, and the final modifications of silicon and the affected area are similar. With higher delay values, the excited zone is smaller, and with higher pulse energy, ablation can be observed. During all experiments, an amorphous silicon ring was formed in the final states, which could potentially serve as a good indicator of temperature. By recording the dynamics of the induced damage, it is possible to observe the change of the reflection coefficient of the material and to relate the change to the ongoing processes. However, it has not been demonstrated in the experiment that a long-term change in the amorphizing properties of silicon can be a suitable indicator of temperature to help identify the entire heat-affected area profile. |
