Abstract
Ultrashort pulsed laser photoinscription of Ti:Sapphire crystals may result in the self-organization of nanoscale material redistribution regions in regular patterns within the laser trace and stress-induced birefringence around the laser trace. We report on the formation of anisotropic optical waveguides in Ti:Sapphire by a procedure that involves femtosecond laser inscription of adjacent nonguiding birefringent traces with nanopatterned crosssections and the accumulation of stress birefringence in the region between. Double parallel line structures with a separation of 25μm with vertical and horizontal nanoscale arrangements were written with a choice of orthogonal polarizations. Due to anisotropic light scattering on periodic nanostructures and stress-induced birefringence in the central zone, remarkable polarization dependent guiding effects were observed as a function of the microscopic geometry of the structures. Building on this polarization sensitivity, several structure such as 3 × 3 waveguide arrays, diamond and hexagon patterns are also investigated.
Highlights
Femtosecond direct laser writing (DLW) of transparent materials is a reliable and powerful micromachining technique emerged in the recent years
When a femtosecond pulse is focused inside a dielectric material, the energy is only deposited in the vicinity of the focal spot due to a combination of nonlinear multi-photon absorption and avalanche ionization
We firstly describe the structure and polarization dependent properties of the double track stress-confined waveguides in Ti:Sapphire in comparison to the LiNbO3 crystals and fused silica, correlating the stressed refractive index change, core birefringence, and
Summary
Femtosecond (fs) direct laser writing (DLW) of transparent materials is a reliable and powerful micromachining technique emerged in the recent years In such a way, a wide range of three-dimensional (3D) photonic devices manufactured using this method has been demonstrated in glasses and crystals [1,2]. A certain irradiation dose and as a function of the material, a succession of dense and low density layers may appear, with subwavelength periodicities. In these processes, the laser electric field direction is a main factor in controlling both excitation efficiency and subsequent polarization of the dielectric matrix that assists the formation of ordered nanogratings. The dynamics of the nanogratings growth may involve collective electronic oscillations and local changes in polarizabilities which, due to a modulation of energy deposition and hydrodynamic matter redistribution, lead to the formation of a rippled structure under the condition of appropriate material relaxation
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