Abstract
Calcium Fluoride (CaF2) was selected owing to its cubic symmetry and excellent luminescence properties as a crystal of interest, and ultrafast laser inscription of in-bulk double-track waveguides was realized. The guiding properties of these waveguides in relation to the writing energy of the femtosecond pulse are presented. The modified double-track waveguides have been studied by systematic developments of beam propagation experiments and numerical simulations. Furthermore, an adapted model and concepts were engaged for the quantitative and qualitative characterization of the waveguides, particularly for the transmission loss measurements and the three-dimensional refractive index mappings of the modified zones. Additionally, polarization-dependent guiding was investigated.
Highlights
The generalized model of bulk damage, in homogenous dielectric materials by ultrafast lasers, involves a combination of nonlinear absorption processes resulting in the excitation and heating of electrons followed by transfer of this heat energy to the surrounding lattice
direct laser writing (DLW) has been implemented for the functionalization of laser systems and subsystems in high-repetition-rate laser systems by miniaturizing photonic components, such as monolithic mode-locked waveguide lasers [5,6,7,8]
Once the 3D refractive index changes (RIC) is obtained, the 3D spatial mappings of refractive indices are realized by adding the refractive index of CaF2 at 632.8 nm, n = 1.4348, over the entire ensemble of 3D RIC values
Summary
The generalized model of bulk damage, in homogenous dielectric materials by ultrafast lasers, involves a combination of nonlinear absorption processes resulting in the excitation and heating of electrons followed by transfer of this heat energy to the surrounding lattice The deposition of this energy induces, by a variety of mechanisms, refractive index modifications localized over a micrometer-sized volume of the material [1,2,3]. The possibilities of extreme confinement and rapid prototyping of these modifications inside dielectric materials have resulted in the realization of vast ranges of photonic devices, from optical waveguides to more complex photonic circuits This has been a driving force for a flourishing industrial interest in direct laser writing (DLW) inside dielectric materials in the past two and a half decades [4]. Reference [10] provides an excellent review on optical waveguides in crystals describing the writing mechanism and giving an exhaustive overview of the different crystalline materials
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