ABSTRACT
Zinc oxide-zinc tungstate (ZnO-ZnWO4 ) is a self-organized eutectic composite consisting of parallel ZnO thin layers (lamellae) embedded in a dielectric ZnWO4 matrix. The electromagnetic behavior of composite materials is affected not only by the properties of single constituent materials but also by their reciprocal geometrical micro-/nano-structurization, as in the case of ZnO-ZnWO4 . The light interacting with microscopic structural features in the composite material provides new optical properties, which overcome the possibilities offered by the constituent materials. Here remarkable active and passive polarization control of this composite over various wavelength ranges are shown; these properties are based on the crystal orientation of ZnO with respect to the biaxiality of the ZnWO4 matrix. In the visible range, polarization-dependent polarized luminescence occurs for blue light emitted by ZnO. Moreover, it is reported on the enhancement of the second harmonic generation of the composite with respect to its constituents, due to the phase matching condition. Finally, in the medium infrared spectral region, the composite behaves as a metamaterial with strong polarization dependence.
ABSTRACT
We investigate the possibility of spatially and spectrally controlling the thermal infrared emission by exploitation of the Yagi-Uda antenna design. Hybrid antennas composed of both SiC and Au rods are considered and the contributions of emission from all the elements, at a given equilibrium temperature, are taken into account. We show that the detrimental effect due to thermal emission from the not ideal parasitic elements drastically affect the performances of conventional thermal Au antennas in the 12 µm wavelength range. Nevertheless, our results show that the hybrid approach allows the development of efficient narrow-band and high directivity sources. The possibility of exploiting the Yagi-Uda design both in transmission and in reception modes, may open the way to the realization of miniaturized, efficient, robust and cheap sensor devices for mass-market applications.
ABSTRACT
By means of an ultrafast opto-acoustic technique we study the nanoindentation of thin chromium films on sapphire substrates using a ceramic ball bearing. Acoustic pulses at approximately 40 GHz returning from the film-indenter interface allow the film indentation profiles to be probed to sub-nanometer resolution over contact areas approximately 25 microm in radius. The deformation of the films during loading is thereby revealed. Furthermore, thermal wave imaging of the contact at megahertz frequencies is simultaneously achieved.
