Among recent advanced manufacturing techniques introduced over the last decades, non-ablative femtosecond laser processing has gained a lot of attention thanks to its applicability to a variety of substrates and its unique ability to locally process transparent materials in their volumes. [1-3]. The laser-induced taxonomy of structural modifications is rich and, despite the extreme brevity of the laser-matter interaction, includes nano-crystallization events as recently reported in various amorphous substrates [4,5]. Yet, the mechanism leading to these nano-crystallization phenomena driven by locally extreme exposure conditions, similar to warm-dense state of matter (WDM), remains elusive.

Thus, understanding phase transitions initiated upon modification with an ultrashort femtosecond infrared (IR) laser is key to tailor the properties of the modified volumes. One promising class of materials undergoing phase transformations are metallic glasses. In tellurite-based glasses, the interaction with an ultrashort IR laser leads to metallic grains inside the dielectric environment [4]. These transformations allow for local changes in the electrical conductivity, leading to the design of arbitrarily shaped conducting channels in an insulating material. Near the surface, the transformations also enable photoconductive functionalization [6].

Here, I present operando X-ray microdiffraction experiments studying in situ nano-crystallization dynamics initiated by non-linear material interaction of an ultrafast IR laser with the tellurite-based glass 80TeO2-10WO3-10K2O (mol%, TWK). The measurements allowed for identification of crystalline phases formed in the dielectric originating from the modification with non-linear laser absorption. We apply different laser absorption conditions namely varying the repetition rates, pulse sequences, and pulse energies for one modification voxel. Moreover, ex situ tomographic experiments reveal the distribution of the crystallites in the volume near the surface, combining the diffraction information with enhanced spatial resolution.

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[4] G. Torun, T. Kishi, Y. Bellouard, Direct-write laser-induced self-organization and metallization beyond the focal volume in tellurite glass, Phys. Rev. Materials 5, 55201 (2021)
[5] R. Ricca, Y. Bellouard, Single-Layer Subwavelength Femtosecond-Laser-Induced Confined Nanocrystallization in Multistack Dielectrics, Phys. Rev. Applied 19, 44035 (2023)
[6] G. Torun, A. Romashkina, T. Kishi, Y. Bellouard, Femtosecond-laser direct-write photoconductive patterns on tellurite glass, Phys. Rev. Applied 21, 14008 (2024)