Non-linear optical properties of Li2O–TiO2–P2O5 glasses

The non-linear optical properties of Li2O–TiO2–P2O5 glasses were measured by Z-scan technique using a nanosecond pulsed laser. The non-linear refractive index (γZ) estimated from Z-scan normalized transmittance was considered to include the optical Kerr effect (γK), the thermo-optic effect (γT) and the resonant non-linearity (γR) related to Ti3+ ions of which content was increased with TiO2 content. The sign of γZ for glasses with 5 and 10 mol% TiO2 was positive, whereas for glasses with 15 and 20 mol% TiO2 it was negative. The γT of all the glasses in the present work was negative due to the negative temperature coefficient of linear refractive index (dn/dT), and decreased with increasing TiO2 content, and was considered to be dominated by the two-photon absorption. For Ti3+-containing 50Li2O · 15TiO2 · 35P2O5 glass with negative γZ (−1.78 × 10−18 m2 W−1), each of these three contributions was evaluated. The thermo-optic γT of the Ti3+-containing glass was determined to be −22.11 × 10−18 m2 W−1. Using the γZ and γT for the Ti3+-free glass made by remelting the Ti3+-containing glass at 1000 °C under O2 atmosphere, the optical Kerr γK of the Ti3+-containing glass was found to be positive (11.87 × 10−18 m2 W−1). The resonant γR of the Ti3+-containing glass was found to be positive (8.46 × 10−18 m2 W−1). As a result, it was concluded that negative γZ of the Ti3+-containing glass resulted from negative thermo-optic γT.