Ultrashort laser-induced nanogratings in glass: insights from numerical modeling
Abstract
Three-dimensional nanostructures inside glasses, such as volume nanogratings (VNG), are known to be created by ultra-short laser interactions [1-4]. These structures have many potential applications in photonics, nanofluidics, material marking (ex: fighting with counterfeiting), etc. Contrary to the periodic surface structures, clear understanding of the physical origin of these structures is still lacking.
Here, numerical modeling of ultrashort laser interactions with glasses containing laser-induced inhomogeneities is performed to explain the periodic organization of nanoplasmas elongating perpendicular to the laser polarization and leading to VNG formation. In particular, two cases are considered:
-First, structures with a periodicity corresponding to laser wavelength in the irradiated material are attributed to the interference of the incident and the inhomogeneity scattered waves. These structures are shown to evolve from a sharp interface between two regions with different effective refractive indexes.
-Second, structures periodicity is defined by the local concentration of the laser-induced inhomogeneities. These structures are attributed to a coherent multiple scattering and require a smooth concentration profile. Sub-wavelength periodicity of these structures, local polarization dependence and the laser conditions for nanostructure formation similar to experimentally reported data make them a likely candidate for the explanation of VNG origin in glasses [5].
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