Abstract
This work investigates the role of a B2O3 addition (up to 21 mole %) into a lithium niobium silicate glass matrix, focusing on the orientational dependency of second harmonic generation (SHG), induced after femtosecond laser irradiation. We detected the sharp emission of light at 515 nm, characteristic of SHG, in both static and scanning configurations, using pulse energy, repetition rate, and laser polarization as varying parameters. Among the results to highlight, the SHG signature appears within a few seconds in highly doped B2O3 glass, i.e., one order of magnitude smaller than in B2O3-free glass. Additionally, we found that the orientability of the polar axis of LiNbO3 nanocrystals by writing laser polarization can be obtained in glasses when SiO2 is substituted with B2O3. These preliminary results open the door to the fabrication of crystal / glass based photonic devices with lower laser power deposited and much faster crystallization kinetics.
Highlights
Femtosecond laser direct writing (FLDW) is a powerful and versatile tool enabling a large variety of optical components to be fabricated in transparent materials such as glasses (e.g.Bragg gratings, waveguides, graded index lenses, birefringent optics) [1,2,3]
We revealed the creation of polarization dependent χ(2) by the second harmonic generation (SHG) detection and confirmed this is related to LiNbO3 nanocrystals by electron backscattered diffraction (EBSD)
As the deposited power (P = RR x Ep ) increases, the area of the modified region becomes wider than the spot size, which is characteristic of thermal accumulation in and around the focal spot (of radius w0 ∼ 1.2λ/(2NA) ∼ 1 μm)
Summary
Femtosecond (fs) laser direct writing (FLDW) is a powerful and versatile tool enabling a large variety of optical components to be fabricated in transparent materials such as glasses (e.g. Bragg gratings, waveguides, graded index lenses, birefringent optics) [1,2,3]. In addition to surface modifications, the femtosecond laser irradiation has allowed the 3D-nanostructuring of optical properties induced by permanent effects on material structure. A particular focus is about fs-laser crystallization of LiNbO3 in silicate matrix, a crystal that allows many applications in different fields because of its properties: ferroelectricity, pyroelectricity, piezoelectricity and a large second order susceptibility.
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