Erasure of nanopores in silicate glasses induced by femtosecond laser irradiation in the Type II regime
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Erasure of nanopores in silicate glasses induced by femtosecond laser irradiation in the Type II regime Maxime Cavillon1 · Yitao Wang1 · Bertrand Poumellec1 · François Brisset1 · Matthieu Lancry1 Received: 15 June 2020 / Accepted: 7 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract 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. Keywords Femtosecond laser · Nanogratings · Silicate glasses · Thermal stability
1 Introduction Optical devices capable to withstand and operate at high temperatures (> 800 °C) for a long period of time (e.g., hundreds of hours) are attractive for many applications, including aircraft engine monitoring, fuel bed combustors, long lifetime optical data storage or fiber lasers [1–3]. Within the tools at one’s disposal to fabricate devices in both fiber and bulk glass materials, femtosecond laser-direct writing (FLDW) is particularly interesting. Indeed, FLDW is a versatile technique that enables high peak powers to induce local three-dimensional (3D) modifications inside the glass subtract, due to the nonlinear absorption processes involved during the laser light–matter interaction. One of the unique features of FLDW is the possibility to induce self-organized nanogratings, within the so-called Type II regime [4]. In addition, nanogratings have been reported in a variety of glasses, including silica, germanates, silicates, borosilicates [5, 6]. * Maxime Cavillon maxime.cavillon@universite‑paris‑saclay.fr 1
Institut de Chimie Moléculaire et des Matériaux d’Orsay (ICMMO/SP2M/MAP), Université Paris-Saclay, CNRS, 91405 Orsay Cedex, France
In silica, these nanogratings can survive beyond 1000 °C for several hours [7], and are composed of regularly spaced porous nanolayers (typically few tens of nm thickness, with a period of about 300 nm). The latter are filled with nanopores having their size and number being a function of the laser parameters as well as the glass material [8]. Upon an increase in temperature, Type II regime laser-induced modifications would be accompanied by changes in the glass st
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