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Asymmetric metal-dielectric nanostructures are demonstrated superior optical properties arising from the combination of strong enhancement of near-fields and controllable scattering characteristics which originate from plasmonic and high-index dielectric components. Here, being inspired by the recent advances of the asymmetric hybrid nanoparticles fabrication [Dmitry Zuev, et al., Adv. Mater. 28, 3087 (2016)], we suggest and study numerically a novel type of hybrid dimer nanoantennas. The nanoantennas consist of asymmetric metal-dielectric (Au/Si) nanoparticles and allow tuning of the near- and far-field properties via laser induced reshaping of the metal part at the nanoscale. We demonstrate an ability to modification of the scattering properties, near-field distribution profilis, normalized local density of states, and radiation patterns of the nanoantenna upon the laser reshaping. The parameters used to investigate these effects correspond to experimentally demonstrated values. [ABSTRACT FROM AUTHOR]

Photoconductive antennas are promising sources of terahertz radiation that is widely used for spectroscopy, characterization, and imaging of biological objects, deep space studies, scanning of surfaces, and detection of potentially hazardous substances. These antennas are compact and allow for generation of both ultrabroadband pulses and tunable continuous wave terahertz signals at room temperatures, with no need for high-power optical sources. However, such antennas have relatively low energy conversion efficiency of femtosecond laser pulses or two close pump wavelengths (photomixers) into the pulsed and continuous terahertz radiation, correspondingly. Recently, an approach to solving this problem that involves known methods of nanophotonics applied to terahertz photoconductive antennas and photomixers has been proposed. This approach comprises the use of optical nanoantennas for enhancing the absorption of pump laser radiation in the antenna gap, reducing the lifetime of photoexcited carriers, and improving the antenna thermal efficiency. This Review is intended to systematize the main results obtained by researchers in this promising field of hybrid optical-to-terahertz photoconductive antennas and photomixers. We summarize the main results on hybrid THz antennas, compare the approaches to their implementation, and offer further perspectives of their development including an application of all-dielectric nanoantennas instead of plasmonic ones. [ABSTRACT FROM AUTHOR]

Tailoring of the near‐field properties of the nanostructures is a significant task for the control of radiation of nanoscale light sources as well as for sensing applications. Generally, this task is solved in plasmonic oligomers on the fabrication step by the choice of geometry or by controlling the excitation light during the experiments. Here, the pronounced modification of the near‐field pattern in hybrid gold‐silicon oligomers by femtosecond laser reshaping by visualizing it with aperture‐type near‐field optical microscope is demonstrated. This effect correlates with a moderate red‐shift of the broadband magnetic dipole resonance of the structure that occurs upon reshaping the gold component of the oligomers. The proposed all‐optical near‐field reconfiguration approach makes hybrid oligomers a promising platform for on‐demand engineering of local field enhancement in metadevices for data recording and sensing. An exciting opportunity to control near field at the nanoscale by modifying the gold component of hybrid gold‐silicon oligomers by femtosecond laser pulses is reported. The shape of oligomers can be changed to enhance the confinement of optical fields accompanying a moderate redshift of the magnetic dipole resonance. This method can be applied for light sources control, sensors and data recording. [ABSTRACT FROM AUTHOR]