Application and validation of a viscosity approach to the existence of nanogratings in oxide glasses

Nanogratings are self-organized and sub-wavelength birefringent structures that are formed upon the action of high intensity ultrashort light pulses in the bulk of a transparent material. They have found interest in optics/photonics, microfluidics, optical data storage or sensing applications. However, the ability to successfully imprint 3-dimensional (3D) nanogratings in silicate glasses is a strong function of the glass composition. In this work, we investigate the role of glass viscosity on the ability to induce these nanogratings. We first study the nanogratings formation window in an energy-repetition rate laser parameter landscape for five common oxide glasses: SiO2 (Suprasil), GeO2, and Schott glasses AF32, Borofloat, and BK7. Secondly, and based on previous work, we define a domain of existence of the nanogratings using viscosity-based arguments. The lower limit corresponds to a temperature at which the viscosity is ~106.6 Pa⋅s, where nanocavitation of the glass occurs, forming the nanopores that compose the nanogratings. An upper temperature limit, set for a viscosity value of ~103.0 Pa⋅s, relates to either collapse or growth of the nanopores, resulting in the erasure of the nanopores, hence the nanogratings. The experimental results agree with the predictions made by this viscosity approach and literature data. This work opens the door to future glass viscosity engineering to maximize 3D nanogratings imprinting