Study On Femtosecond Filamentation In Noble Gases And Femtosecond Pulse Carving On LiNbO₃ Crystals

This thesis includes two parts of research: the spectrum expansion of femtosecond through filamentation in noble gas and the periodically poling of LiNbO₃ (LN) with femtosecond laser carving technique. To achieve intense monocycle laser pulses, sufficient spectral width is required. Due to the nonlinear interaction and ionization, the spectrum of femtosecond laser pulses can be expanded through filament in noble gases. One of the purposes of this study was to investigate the dependence of the spectrum width on the pulse energy, pulse width, and pressure of noble gases. In the second part, the preliminary numerical simulation and the experiment of poling in femtosecond laser carved LN crystal is described. The mean contents and innovation are listed as follows.1. The historical review of laser and femtosecond laser interaction with gas and solid state materials was presented. We focused on how to achieve intense monocycle pulses in recent years.2. A theoretical description was given to summarize the self-focusing during laser propagation and the condition of filamentation. From the mathematic representation, we derived the dependence of the filament length on the characterization of the incident pulses.3. Investigation on filamentation was examined using a capillary as a probe, for various parameters. They are very useful in next step of pulse compression.4. As the second part, the principle of femtosecond laser machining was introduced for preparation of writing PPLN with those pulses.5. Experiment on machining LiNbO₃ crystal by femtosecond laser pulse and high electric field poling was described. The poling pattern was observed by microscope and machining parameter influences on the electric field distribution in the crystal, though the fully poling has not been fulfilled.6. Summarization of my work and outlook of the future experiment.