Erasure of nanopores in silicate glasses induced by femtosecond laser irradiation in the Type II regime

Optical devices fabricated by femtosecond (fs) laser within the Type II regime are of interest for high temperature applications (> 800 °C). fs-Type II regime is characterized by the formation of self-organized nanogratings, which are composed of regularly spaced porous nanolayers with nanopores having a typical size of a few tens of nm. In this work, we first investigate the evolution of the nanopore size distribution as a function of fs-laser writing speed and pulse energy, as well as a function of annealing temperature after fs-laser irradiation. Then, the thermal stability of such nanopores is numerically investigated through the use of the Rayleigh–Plesset (R–P) equation, and is compared with experimental data. The R–P equation provides insights into the temperature range at which the nanopores would ultimately collapse, serving as a design tool for future high temperature fs-Type II based devices. The key role of glass viscosity and nanopore diameter on the overall thermal stability is also discussed.