Reconfigurable VO metasurfaces with hybrid electro-optical control: manipulating THz radiation with 0.3 W/cm light.

Dynamicallyprogrammable metasurfaces capable of manipulating terahertz (THz) wavefronts in various manners depending on external controls are highly desired for next-generation wireless communication systems and new tools for THz diagnostics. Such metasurfaces may utilize the insulator-to-metal transition in , which can be induced both electrically and optically. Optical control is especially convenient for individual addressing to each meta-atom, but it is hampered by the high optical switching threshold of .

Photothermal Effect and Phase Transition in VO Enhanced by Plasmonic Particles.

Phase change metasurfaces based on VO, which are pre-heated with electric current and optically addressed by projected structured light hologram, are considered to become a new paradigm in programmed THz/middle IR flat optics. Macroscopic quasi-homogeneous arrays of Au nanoparticles show large near IR absorption and a significant photothermal effect capable of boosting a light-triggered switching of VO and are to be carefully examined. We propose a new approach to simultaneously probe the altered temperature and electric conductivity of a hybrid Au particle-VO film composite by monitoring a phase shift and attenuating a surface acoustic wave in a YX128° cut LiNbO substrate.

Coherent optical phonons of ZnO under near resonant photoexcitation.

Ultrafast electron-phonon coupling dynamics in ZnO are investigated by degenerate pump-probe reflectivity measurements using near resonant 400 nm light. Because of the below-gap excitation, photocarriers are excited primarily from deep levels of intrinsic point defects. At least six coherent phonon modes, including two E(2) modes and their combination, longitudinal optical (LO) mode and its overtone (2LO), are observed.

Spatial fluctuations of optical emission from single ZnO/MgZnO nanowire quantum wells.

MgZnO/ZnO quantum wells on top of ZnO nanowires were grown by pulsed laser deposition. Ensembles of spatially fluctuating and narrow cathodoluminescence peaks with single widths down to 1 meV were found at the spectral position of the quantum well emission at 4 K. In addition, the number of these narrow QW peaks increases with increasing excitation power in micro-photoluminescence, thus pointing to quantum-dot-like emission centers.

Whispering gallery modes in nanosized dielectric resonators with hexagonal cross section.

The size dependence of whispering gallery modes in dielectric resonators with hexagonal cross section has been observed within the visible spectral range for cavity diameters comparable to the light wavelength. As a model system single, tapered, high aspect ratio zinc oxide nanoneedles were analyzed. They enable systematic investigations as a function of the resonator diameter down to the nanometer regime.