Material Processing Of Dielectrics With Temporally Asymmetric Shaped Femtosecond Laser Pulses On The Nanometer Scale

摘要

Laser material processing of dielectrics with temporally asymmetric femtosecond laser pulses of identical fiuence, spectrum, and statistical pulse duration is investigated experimentally. To that end single shot structures at the surface of fused silica as a function of fiuence and pulse shape are analyzed with the help of scanning electron microscopy. Structures for the bandwidth limited pulses show the known expansion in structure size with increasing laser fiuence approaching the diffraction limit, which is 1.4 μm for the 0.5NA microscope objective used. In contrast, structures from the asymmetric pulses are remarkably stable with respect to variations in laser fiuence and stay below 300 nm despite doubling the fiuence. Different thresholds for surface material modification with respect to an asymmetric pulse and its time reversed counterpart are attributed to control of different ionization processes.