Highly Efficient Super-Continuum Generation on an Epsilon-Near-Zero Surface.

The efficient super-continuum (SC) generation on a surface via a high-order photo-electron interaction is a great challenge for integrated optics because the surficial nonlinear optical efficiency is usually limited by finite light-matter interaction length and electric field intensity. Nowadays, epsilon-near-zero (ENZ) materials, showing infinite enhanced electronic field in theory, provide a kind of new platform to obtain a giant nonlinear response on the surface. Here, under the irradiation of a multiwavelength laser, an exotic and efficient SC generation from 406 to 1100 nm on the ENZ aluminum-doped zinc oxide surface was experimentally demonstrated by diversified nonlinear processes, including second harmonic generation, third harmonic generation, four wavelength mixing, and cascading stimulated Raman scattering. Particularly, an unprecedented nonlinear conversion efficiency of 3.94% W, 16 orders of magnitude higher than the common surface case (about 10% W), was presented.