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 \pm 7 \times {10^{ - 16}}\;{{\rm cm}^2}/{\rm W} $ at $ 1.2\,\,\unicode{x00B5}{\rm m} $, $ 81 \pm 23 \times {10^{ - 16}}\;{{\rm cm}^2}/{\rm W} $ at $ 2.0\,\,\unicode{x00B5}{\rm m} $, and $ 100 \pm 15 \times {10^{ - 16}}\;{{\rm cm}^2}/{\rm W} $ at $ 2.4\,\,\unicode{x00B5}{\rm 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.
© 2020 Optical Society of America
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