Contribution To Nano Or Micro Crystallization Induction In Silica-based Glasses By Femtosecond Laser Irradiation

Femtosecond laser processing in transparent materials is promising owing to the accessible control of energy deposition in time and in space. In this regime, it opens fantastic opportunities to manufacture novel multifunctional composite materials by manipulating the size, shape and orientation of nonlinear crystals with intrinsic symmetry embedded in glasses. This dissertation mainly contributes to the control of nano or micro crystallization inside silica-based glasses for the development of novel multifunctional electro-optical materials by femtosecond laser irradiation. We demonstrate the feasibilities of femtosecond laser materials processing for re-shaping linear and non-linear optical properties in silica-based glass by inducing or fabricating different micro/nanoclusters as well as their shapes and orientation (especially asymmetric clusters), sizes, and distributions (at the sub-micrometer scale).In this thesis, it firstly covers a chapter for the investigation on ultrafast asymmetric orientational writing in pure silica as well as in silica-based glass in order to well master the laser writing. We discuss the effects of the laser parameters on asymmetric writing such as writing speed and the laser polarization by the femtosecond-laser generated optical properties and structures, e.g., birefringence, phase change and surface topography of the cross section of laser tracks. The mechanism of orientational dependent writing is likely due to the oblique pulse front tilt affected by the polarization orientation plane leading to different anisotropic photosensitivity.3D photo-precipitation of oriented LiNbO2-like crystals in glass with femtosecond laser irradiation is achieved at high repetition rate (typ.300 kHz). Oriented crystals with their polar axis mostly aligned with the laser scanning direction have been fabricated by manipulation of the temperature gradient in adjusting the laser parameters. Second harmonic generation (SHG) microscopy demonstrates optical activity of crystalline features and provides some orientation information suggestive of certain dominant or favored orientations. Electron back-scattering diffraction (EBSD) results provide more detailed local crystal orientation information and illustrate interesting features of the structure of the lines, with regions of distinctly different grain sizes and orientations. It provides interesting new data for femtosecond laser crystallization inside bulk glass of a crystalline phase of significant interest for commercial optics. Furthermore, modeling the temperature gradient was proposed for better understanding the formation mechanism of the orientation of femtosecond laser-induced crystallization when the laser is moved (not only in the static mode).Quasi-spherical or quasi-rod gold nanoparticles in silica-based glass can be re-shaped by femtosecond laser irradiation studying through their properties, and their orientation appears to be parallel to the written lines. In this work, we prepared the gold-doped glass by a conventional melt-quenching method. Gold nanoparticles in the size range of 3-4 nm were precipitated by post heat-treatment. After ultrafast laser irradiation, optical absorption, birefringence and dichroism measurements are performed to investigate the modification of gold nanoparticle shape in glass. Theoretical simulations have been carried out to interpret the experimental results based on the Gans'theory and Drude model together with the known dielectric constants of gold. They show that a small fraction of gold nanospheres are transformed into nanorods and nanopellets with the aspect ratio of 1.8 and 0.5, respectively, and that they are oriented along the writing laser polarization or the direction writing.Furthermore, feasible applications and efficient design strategies are also referred for future devices based on micro/nanoclusters 3D precipitation, shaping and orientation mastering.