The Set Up Of The Femtosecond Pulse Shaping System And Its Application In Controlling Of The Ablation Process

The technique of pulse shaping by femtosecond laser is an important experimental method in which the parameters (such as phase, laser intensity and so on) of the input pulse are modulated by special shaper tool, and the pulse train including several pulses between which special delay time are formed. Since the ultrafast dynamics process in microcosmic system can be distinguished by this output pulse train, the pulse shaping technique is dramatically concerned recently. The work of this thesis was actually based on the realization and application of the pulse shaping technique.In the work of this thesis, the setup of the reflection-type and transmission-type 4f pulse shaping apparatus based on the Fourier space-time transforming has been finished. Some optimization methods were introduced for avoiding the problems in the setup course. The non-dispersion outputs have been realized in the finished apparatus. Then, a series of masks were made by printing film and a series of pulse train waveforms were produced successfully. Spatial light modulation (SLM) was used for the exactitude of the output pulse train, and the function relationship between the pixel-wavelength and the phase- voltage on the SLM were calibrated. By using SLM, a lot of defined shaped pulse waveforms were produced, such as the THz trains which have six sub-pulses apart 441fs from each other; the double pulses which have 730fs width and variable distances between each other. The experimental results were consistent with the theoretical predictions.In order to check out the performance of the pulse shaping system, the defined pulse trains were exported by SLM: the pulse trains have fixed waveform and different time interval; the trains have fixed time interval and different numbers of pulses; and the single pulses have different width in femtosecond spectrum. Using the defined pulse waveforms, the semiconductor Si, GaAs and the electrolyte SiO2 were ablated. In the experiment the variety of output pulse waveforms have different influence on different material samples. Some simple explanation was made for these experimental phenomenons:To the semiconductor Si, which has a narrow forbidden band, the effect of multi-pulses exhibits that former pulses melt sample surface resulting the absorption coefficient of the sample surface is enhanced, and the energy density in surface melting layer is enhanced, thus, the efficiency of ablation is improved.To the electrolyte SiO2 which has a wide forbidden band, the effect of multi-pulses exhibits that the all energy were distributed into each sub-pulses; the ionization probability decreases with decreasing the laser intensity, so that the efficiency of ablation is weaken.Fifty times optical microscope was used to observe the surface figure of the ablated sample. The surface figure ablated by the single pulse and multi-pulses illustrated some difference. The fact above represented that the pulse shaping affect ablating process remarkably.