Ultrafast imaging of transient electronic plasmas produced in conditions of femtosecond waveguide writing in dielectrics

Femtosecond laser-induced plasmas in bulk dielectrics are imaged under waveguide writing conditions, for different polarizations, pulse durations, and processing depths, and their temporal evolution is measured using ultrafast pump-probe microscopy. The irradiation beam profile is elliptically shaped yielding a disklike focal volume. We demonstrate for doped phosphate glass that increasing the pulse duration improves the spatial distribution of deposited energy by minimizing beam filamentation and prefocal depletion effects. As a consequence, energy deposition in the desired volume is greatly enhanced. Our results identify key parameters for optimizing femtosecond laser processing of dielectrics and different strategies to minimize energy loss channels.