Femtosecond filamentation, supercontinuum generation and determination of n₂ in polycrystalline SBN

We demonstrate that polycrystalline strontium barium niobate (SBN) serves as an excellent nonlinear material for supercontinuum (SC) generation in the near- and mid-infrared, as pumped by femtosecond pulses in the regions of its normal, zero, and anomalous group velocity dispersion. We also show that broadband, octave-spanning planar second-harmonic emission generated via random quasi phase matching usefully serves to precisely monitor focusing/refocusing cycles of a filament and to determine position of the nonlinear focus in particular, which was used to estimate the nonlinear index of refraction of the material applying Marburger’s law. The measured $ {n_2} $n2 values are remarkably large: $ 44 \pm 7 \times {10^{ - 16}}\;{{\rm cm}^2}/{\rm W} $44±7×10−16cm2/W at $ 1.2\,\,\unicode{x00B5}{\rm m} $1.2µm, $ 81 \pm 23 \times {10^{ - 16}}\;{{\rm cm}^2}/{\rm W} $81±23×10−16cm2/W at $ 2.0\,\,\unicode{x00B5}{\rm m} $2.0µm, and $ 100 \pm 15 \times {10^{ - 16}}\;{{\rm cm}^2}/{\rm W} $100±15×10−16cm2/W at $ 2.4\,\,\unicode{x00B5}{\rm m} $2.4µm, and thus imply very low energy (below 100 nJ) and power (below 1 MW) thresholds for filamentation and SC generation in the infrared spectral range.