Modeling of Ultrafast Phenomena Induced by Ultrashort Pulsed Lasers

We present an experimental and numerical study of the spatio-temporal evolution characteristics of filamentary regions induced in dielectric materials by femtosecond (300 fs) and picosecond (2 ps) pulses. The evolution of the filamentary region was observed using precise and extensive time-resolved measurements. In the simulation, the evolution of the ultrashort laser pulse, induced electron density, energy conservation between the electron and lattice system, and changes in the dielectric properties of the material were calculated at each time. The results show that the distribution of filamentary regions, which has been simplified in previous studies to correspond mainly to that of the electron density, can be systematically explained by considering the effect of the electron relaxation time on the material absorptivity. Furthermore, the correspondence between the distribution of the filamentary region and the electron density was found to decrease as the temperature of the system increased. These results support recent reports that gradual heating of the material using relatively long pulses improves the modification efficiency, and thus, the findings of this study are expected to lead to the discovery of more efficient processing methods in the future.