Refractive index modification in fluoro-borate glasses containing WO3 induced by femtosecond laser

•New glasses belonging to the NaF–Na2B4O7–WO3 system were prepared and characterized.•Their glass structure was investigated by Raman spectroscopy.•Homogeneous optical waveguides were inscribed by 800 nm femtosecond pulse exposure.•Positive refractive index change of 5 × 10− 3 has been measured by using QPM technique.

New glasses belonging to the NaF–Na2B4O7–WO3 system have been studied in order to inscribe optical waveguides within their volume through local refractive index modification after irradiation by ultrafast laser pulses. Appropriate addition of NaF to glasses belonging to the pseudo-binary vitreous system Na2B4O7–WO3 has allowed to obtain striae-free bulk glasses of large volume with high content of WO3 (35 mol%). Their physical and structural properties have been investigated through UV–visible spectroscopy, differential scanning calorimetry, densitometry and Raman spectroscopy. The glass of composition (NaF)15–(Na2B4O7)50–(WO3)35 has been then exposed to 800 nm femtosecond pulses of 70 fs width at a repetition rate of 100 kHz from a Ti-sapphire regenerative amplifier system. By varying the input pulse energy and scanning speed, homogeneous optical waveguides were inscribed and a positive refractive index change of the order of 5 × 10− 3 has been measured.