Femtosecond filamentation, supercontinuum generation, and determination of $ {n_2} $n₂ in polycrystalline SBN

Abstract

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 values are remarkably large: 44 ± 7 × 10 − 16 c m 2 / W at 1.2 µ m , 81 ± 23 × 10 − 16 c m 2 / W at 2.0 µ m , and 100 ± 15 × 10 − 16 c m 2 / W at 2.4 µ m , 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.