Strong nuclear contribution to the optical Kerr effect in niobium oxide containing glasses

The electronic and nuclear contributions to nonlinear optical properties of niobium oxide-based glasses have been measured using third-harmonic generation and pump-probe techniques. The results have been found to be in agreement with Hellwarth’s model for niobium oxide $\left({\mathrm{Nb}}_2{\mathrm{O}}_5\right)$ concentrations below $30\mathrm{mol}\%$. Above $30\mathrm{mol}\%$ ${\mathrm{Nb}}_2{\mathrm{O}}_5$, discrepancies with the theoretical model have been observed. It has been found that high niobium ion content induces a change of the local structure within the glass and favors the formation of three-dimensional blocks of corner-sharing ${\mathrm{NbO}}_6$ octahedra. Since similarities with crystalline structures are present, we propose that some specific collective vibrational modes could be at the origin of the extra nuclear contributions to the optical Kerr effect.

Figure 1

THG susceptibility $\left({\sigma }_{1111}^{\left(3\right)}\right)$, Kerr effect susceptibility $\left[\Lambda \right(u=0\left)\right]$, and measured nuclear susceptibility $\left[\Lambda \right(u=0)-{\sigma }_{1111}^{\left(3\right)}]$ versus ${\mathrm{Nb}}_2{\mathrm{O}}_5$ molar concentration.

Figure 2

Functions $G\left(u\right)$ (dashed curve) and $H(d_{1212}^{\left(3\right)};u)$ (full curves) versus time delay between the pump and the probe pulses for a $100\mathrm{fs}$ pulse at $800\mathrm{nm}$ for different ${\mathrm{Nb}}_2{\mathrm{O}}_5$ concentrations.

Figure 3

Absolute polarized (VV) Raman spectra of the borophosphate matrix glasses with different ${\mathrm{Nb}}_2{\mathrm{O}}_5$ concentrations at $1064\mathrm{nm}$.

Figure 4

Absolute depolarized (VH) Raman spectra of the borophosphate matrix glasses with different ${\mathrm{Nb}}_2{\mathrm{O}}_5$ concentrations at $1064\mathrm{nm}$.