Giant Broadband Refraction in the Visible in a Disordered Ferroelectric Perovskite

In this work we report broadband refraction and diffraction experiments in a ferroelectric perovskite, a solid-solution K 0.997 Ta 0.64 Nb 0 .36:Li 0.003 (KTN:Li), that demonstrate an index of refraction of $n > 26$ across the entire visible spectrum. The sample has a natural-occurring room temperature phase that propagates visible light along its normal axis without significant diffraction or chromatic dispersion, irrespective of beam size, intensity, and angle of incidence.