Investigation and control of ultrafast laser-induced nanoscale patterns in bulk dielectric materials
Résumé
Local refractive index changes are the building blocks of laser-induced 3D optical functions in bulk transparent materials, e.g. fused silica. Depending on the regime of interaction, focused ultrashort pulses could induce either positive or negative isotropic smooth refractive index changes (usually denoted as type I) or produce regular nanoscale self-arranging layered structures resulting in form birefringence (type II nanogratings - Fig. 1), a regime which is regularly observed in fused silica [1,2]. Particularly the latter phenomenon is a spectacular and intriguing physical manifestation that allows the development of embedded polarization functions. A spectroscopic study is proposed to reveal the particular electronic and structural transformation of glassy matter in the self-organized subwavelength structures, indicating bond breaking and the abundance in oxygen deficiency. As the spontaneous arrangement is intermediated by electronic excitation, we equally propose a method of real time control and optimization of nanogratings formation in bulk fused silica under the action of ultrashort laser pulse with programmable variable envelopes. Relying on the advantage on the intrinsic anisotropies, the application potential in terms of polarization sensitive optical devices is discussed.