RIKEN Center for Advanced Photonics, Wako, Saitama, Japan
25.09.2018. u 15:00h
IF - predavaonica u zgradi Mladen Paić
This presentation focuses on theoretical and experimental studies of laser second harmonic generation (SHG) in periodically-poled crystals in the range from ns to ps pulse duration. High-intensity and high-efficient SHG operation is inhibited by many side effects associated with dephasing of the involved lased waves caused by generation of non-uniform temperature distributions and plasma generation along the beam propagation. Generation of free electrons by generated second harmonic and accelerated to a high energy by generated pyro-electric field is shown to be able to produce high-density defects and damage in the rear side of the operating crystals. Temperature-controlled experimental study of high-intensity high- frequency ps SHG allowed to find the temperature effect of a single ps pulse. The detailed analysis of the plasma generation kinetics and related recombination pathways related to this experiment allowed to suggest a new modification of the non-equilibrium two-temperature model of short-pulsed laser-matter interaction leading to an excellent agreement with the experiment. This modification is valid for a wide range of laser-matter interactions and related application for operation and processing of dielectric materials for electron density below 1021 cm-3. Finally, we suggest a new scaling estimate for the characteristic time of electron-lattice energy transfer time agreeing well with experimental data for a wide range of materials.