Nonlinear optical properties of tungstate fluorophosphate glasses

The optical nonlinearity of tungstate fluorophosphate glasses, synthesized in the NaPO3-BaF2-WO3 system, was investigated through experiments based on the third-order susceptibility, χ(3). Nonlinear (NL) refraction and NL absorption measurements in the picosecond regime were performed using the Z-scan technique at 532 nm. NL refractive index, n2∝Re χ(3), ranging from 0.4×10−14 cm2/W to 0.6×10−14 cm2/W were determined. The two-photon absorption coefficient, α2∝Im χ(3), for excitation at 532 nm, vary from 0.3 to 0.5 cm/GW. Light induced birefringence experiments performed in the femtosecond regime indicate that the response time of the nonlinearity at 800 nm is faster than 100 fs. The experiments show that χ(3) is enhanced when the WO3 concentration increases and this behavior is attributed to the hyperpolarizabilities associated to W–O bonds.