  Defining microstructures and managing local crystallinity allow the
implementation of several functionalities in thin film technology. The use of
ultrashort Bessel beams for bulk crystallinity modification has garnered
considerable attention as a versatile technique for semiconductor materials,
dielectrics, or metal oxide substrates. The aim of this work is the
quantitative evaluation of the crystalline changes induced by ultrafast laser
micromachining on manganese oxide thin films using micro-Raman spectroscopy.
Pulsed Bessel beams featured by a 1 micrometer-sized central core are used to
define structures with high spatial precision. The dispersion relation of Mn3O4
optical phonons is determined by considering the conjunction between X-ray
diffraction characterization and the phonon localization model. The asymmetries
in Raman spectra indicate phonon localization and enable a quantitative tool to
determine the crystallite size at micrometer resolution. The results indicate
that laser-writing is effective in modifying the low-crystallinity films
locally, increasing crystallite sizes from ~8 nm up to 12 nm, and thus
highlighting an interesting approach to evaluate laser-induced structural
modifications on metal oxide thin films.
