Spectroscopic characterization of different femtosecond laser modification regimes in fused silica

Structural changes associated with femtosecond laser fabrication of waveguides and Bragg gratings in fused silica were analyzed using optical microscopy and laser spectroscopy. Using 800 nm femtosecond lasers with a kilohertz repetition rate and various pulse energies, both smooth and rough modifications were induced. The different modification regimes were characterized by measuring the spectra of the light emitted during writing with the femtosecond laser and collecting fluorescence spectra after femtosecond writing using a low power 488 nm laser as an excitation source. The spectral features observed during and after writing can be used to distinguish the smooth and rough modification regimes, and they assist in understanding the underlying modification mechanisms.. (c) 2007 Optical Society of America.