Large negative refractive index modification induced by irradiation of femtosecond laser inside optical glasses

We report on the refractive index modification (Δn) and its cross sectional profile of the created lines inside the different types of optical glasses, containing BaO, TiO2, or La2O3 as a metal oxide. The lines were fabricated by scanning a stage and focusing the femtosecond laser pulses, 800 nm wavelength, a 250 kHz repetition rate and 200 fs pulse duration, from the Ti:sapphire regenerative amplifier system. The Δn measurements were performed with the qualitative phase microscopy technique. As a result, it was found that the Δn and its sign are different depending on glass types. For example, in the glasses containing TiO2, the Δn became smaller in the modified region and some of them showed relatively large decrease of the Δn, Δn < −0.01, with about 10 μm width. Such a glass material could be useful for the compact optics and optical devices.

Research highlights▶ The refractive index modification (Δn) inside a several optical glasses were investigated. ▶ The Δn was fabricated by the irradiation of femtosecond laser pulses. ▶ The glasses were silicate or borosilicate system containing BaO, TiO2, or La2O3 as a metal oxide. ▶ The Δn and the profiles were measured with the qualitative phase microscopy. ▶ A glass containing TiO2 showed relatively large decrease of the Δn, Δn < −0.01.