Split Hole Resonator: A Nanoscale UV Light Source

Because of strong light absorption by metals, it is believed that plasmonic nanostructures cannot be used for generating intensive radiation harmonics in the ultraviolet (UV) spectral range. This work presents results of investigation of nonlinear optical interaction with a single gold nanostructure, the split-hole resonator (SHR) under the state-of-the-art experimentally realized conditions. To realize interaction with all spectral components of a 6 fs laser pulse several multipole plasmon resonances were simultaneously excited in the SHR nanostructure. To the best of our knowledge, this paper reports for the first time a strong nonlinear optical interaction at the frequencies of these resonances that leads to (i) the second harmonic generation, (ii) the third harmonic generation (THG), and (iii) the light generation at mixed frequencies. The THG near field amplitude reaches 0.6% of the fundamental frequency field amplitude, which enables the creation of UV radiation sources with a record high intensity. The UV THG may find many important applications including biomedical ones (such as cancer therapy)

Multipolar Third-Harmonic Generation in Fishnet Metamaterials

We study the third-harmonic generation from metal–dielectric–metal layered fishnet metamaterials and identify experimentally the multipolar contributions to the generated nonlinear harmonic fields by analyzing the radiation patterns of the emission. We observe that the third harmonic radiated from the fishnet structure is a result of the interference of the electric and magnetic dipoles and the electric quadrupole modes. Our results provide direct evidence of the importance of higher order multipoles in the nonlinear response of fishnet metamaterials, opening new opportunities for enhanced nonlinearities and controlled directionality of nonlinear processes in metamaterials