抄録
The non linear optical properties of glasses are investigated with the object of potential applications as optical devices e.g. amplification and modulation of light, parametric frequency conversion, ultra-fast switching etc. By combining structural, optical and theoretical studies the origin of the third-order optical response has been determined in sodium calcium borophosphate glasses containing increasing proportion of TiO2 or Nb2O5. The values of the third-order susceptibility χ(3) can be analysed on the basis of the bond orbital theory and are directly related to the Ti/Nb d-orbital contributions. For the richest titanium and niobium glasses the clustering of TiOn(n=5,6) or NbO6 entities tends to increase leading to an enhancement of the non linear index n2. More recently Second Harmonic Generation (SHG) has been observed when these glasses were subjected to a dc bias of 3kV at 300°C. The close examination of the glasses surfaces before and after poling brings new ideas about the microscopic origin of this phenomenon.
