Creating unusual structures by ultrashort light pulses in glass

Progress in high power ultra-short pulse lasers has opened new frontiers in physics and technology of light-matter interactions and laser micro-machining. The use of femtosecond lasers to directly write photonic structures deep within transparent media has attracted much attention due to its capability for precise structuring in three dimensions. Recent observations of anisotropic light scattering and reflection from the regions modified by intense femtosecond light pulses in the direction parallel to the polarization of wring laser, have given the evidence of sub-wavelength periodic structures imprinted in irradiated materials. Form birefringence induced by self-organized sub-wavelength index gratings has been also proposed to explain a puzzling phenomenon of uniaxial birefringence of structures written within silica glass. Recently the first direct evidence of self-assembled periodic structures within the bulk of material has been reported. The observed volume grating structures are the smallest (20 nm width) and the strongest (-0.2 index change) ever created by light in transparent materials. Moreover these are the first gratings created by interference of bulk electron plasma waves. Another recent unusual observation is the demonstration that writing by femtosecond laser from left to right can be different from writing in the opposite direction. Structures with broken mirror symmetry and chiral patterns in chalcogenide glass have been demonstrated. In the talk the study of these unusual structures created by ultrashort light pulses is reviewed