Imaging of plasma dynamics for controlled micromachining

Abstract

Femtosecond (fs) microscopy constitutes a powerful tool for imaging laser-induced plasmas, assessing their dynamics (formation and decay), and spatial distribution, as well as quantifying their density. This experimental technique can be applied in different modalities to fs laser processing, revealing a wealth of information on the interaction mechanisms. For the case of surface processing, fs-resolved microscopy has the capability of enabling a link between the plasma properties and the induced material modifications. Fs microscopy inside dielectric materials is similarly a powerful tool for optimizing the structures produced. The technique unveils a number of complex interaction mechanisms taking place, including multiple beam filamentation (MBF), and pre-focal energy depletion that act as important energy loss channels, which deteriorate the spatial distribution of the deposited laser energy. Detailed studies performed with this technique show how these undesirable effects can be minimized by adjusting the processing parameters: pulse duration, energy, polarization, and processing depth. As a consequence, the energy is deposited more efficiently and confined to the focal volume region, leading to the production of structures with optimized performance.