Photosensitivity of barium germano-gallate Glasses Under Femtosecond Laser Writing for Mid-IR Applications
Résumé
Barium germano-gallate (BGG) glasses are attractive glass hosts for photonic applications in the mid-infrared region up to 6 µm. In this work, we investigate the photosensitivity of such glasses under femtosecond laser, with an emphasize on the formation of refractive index changes. Six glasses with varying compositions (including addition of K, Na, Y, and La) were studied. We observed several transformation regimes in the pulse energyrepetition rate landscape: Type I (isotropic refractive index change) and a spatial broadening regime with a phase shift Δφ > 2π rad at 550 nm. This translates into refractive index changes Δn > 10-2 and is comparable to values obtained in most chalcogenide glasses. The effect of glass composition on Δφ appears correlated to the number of non-bridging oxygen (NBO) present in the glass and is brought to evidence by monitoring the Cations/GaO3/2 ratio. This provides a way to design a range of germano-gallate glasses suitable to imprinting high refractive index contrast.
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