Anomalous Anisotropic Light Scattering in Ge-Doped Silica Glass

Extraordinary stability of anisotropic femtosecond direct-written structures embedded in silica glass

“…6 It has been shown that femtosecond laser writing in wide band gap materials can induce an optically isotropic positive index change 1 as high as 3 ϫ 10 −2 ͑type I_fs͒. However, when the material is irradiated above a certain intensity threshold ͑which depends on the material, laser wavelength and pulse duration͒ we observe that the femtosecond written structures are characterized by anisotropic scattering, 7 anisotropic reflection, 8 strong birefringence and average negative index change, 9 due to the formation a self-assembled periodic nanostructures. 10 During the energy absorption process, tunneling, multiphoton and avalanche ionization produce free electrons within the focus of the ultrashort pulsed laser.…”

Embedded anisotropic microreflectors by femtosecond-laser nanomachining

“…Evidence was given here of index inhomogeneities with a period estimated to be ϳ90 nm. 9 Closer inspection of Fig. 4 shows an additional smaller peak at 835 nm.…”

“…6,7 Although molecular defects caused by such intense irradiation have been identified in fluorescence, electron-spin resonance and other studies, 8 the mechanism of induced modifications in glass is still not fully understood. Moreover, such structures in Ge-doped silica 9 and other glass materials 10 show an unexpected anisotropic light scattering which is dependent on the plane of light polarization. This has been interpreted in terms of photoelectrons moving along the direction of light polarization inducing index inhomogenities.…”

“…Anisotropic index inhomogeneities are then induced by electrons moving along the direction of light polarization. 9 By analogy to the mechanism ascribed to cause surface ripples on materials ͑i.e., interference initiated by a coupling between incident laser and a surface-plasma wave͒, 12 we further suggest that the self-organized nanostructures are similarly produced by a pattern of interference between the incident laser radiation and a plasmon-polarition wave generated within the sample. Positive feedback leads to exponential growth of the periodic nanostructures in the plane of light polarization, which become frozen within the material.…”

Exciton mediated self-organization in glass driven by ultrashort light pulses

“…4 A decade ago, highly ordered subwavelength structures with features smaller than 20 nm were discovered in the ultrafast laser irradiated volume of SiO 2 glass, 5 which were found to be responsible 6 for the induced optical anisotropy reported earlier. 7,8 Despite several attempts to explain the peculiar self-organization process, the formation of these nanostructures still remains debatable. 5,9 The effect of nanograting formation has already found numerous applications for polarization control devices [10][11][12] and microfluidics.…”