Dynamics of Femtosecond Laser Modification Inside Fused Silica

Abstract

This paper discusses the dynamics of fs-laser modification in fused silica by tightly focusing (NA = 0.25) a 200 fs, 800 nm pump probe. Transmission spectroscopy is performed during a pump-probe experiment with the 800 nm (near infrared) laser and generated supercontinuum light filtered around roughly 660 nm (visible) and 1100 nm (infrared) as probe. In the visible and near infrared spectrum a consistent drop of 40-70% in transmission is seen when pump and probe are temporally overlapped. Within 1 ns after modification the transmission is recovered to its value before modification. In the infrared spectrum a drop in transmission is seen but the transmission plots show unexplainable behavior, probably due to the instability of the generated infrared light. Finally, a difference in time of arrival of different wavelengths is shown to be in the order of a few picoseconds which is confirmed by a ray-tracking model.