Passive radiative cooling draws heat from surfaces and radiates it into space as infrared radiation to which the atmosphere is transparent. However, the energy density mismatch between solar irradiance and the low infrared radiation flux from a near-ambient-temperature surface requires materials that strongly emit thermal energy and barely absorb sunlight. We embedded resonant polar dielectric microspheres randomly in a polymeric matrix, resulting in a metamaterial that is fully transparent to the solar spectrum while having an infrared emissivity greater than 0.93 across the atmospheric window. When backed with a silver coating, the metamaterial shows a noontime radiative cooling power of 93 watts per square meter under direct sunshine. More critically, we demonstrated high-throughput, economical roll-to-roll manufacturing of the metamaterial, which is vital for promoting radiative cooling as a viable energy technology.

http://science.sciencemag.org/content/sci/early/2017/02/08/science.aai7899.full.pdf

Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling

Metadevices based on dielectric nanostructured surfaces with both electric and magnetic Mie-type resonances have resulted in the best efficiency to date for functional flat optics with only one disadvantage: a narrow operational bandwidth Here we experimentally demonstrate broadband transparent all-dielectric metasurfaces for highly efficient polarization manipulation We utilize the generalized Huygens principle, with a superposition of the scattering contributions from several electric and magnetic multipolar modes of the constituent meta-atoms, to achieve destructive interference in reflection over a large spectral bandwidth By employing this novel concept, we demonstrate reflectionless (∼90% transmission) half-wave plates, quarter-wave plates, and vector beam q-plates that can operate across multiple telecom bands with ∼99% polarization conversion efficiency

/pdf/invited-article-broadband-highly-efficient-dielectric-h6iade538p.pdf

Invited article: Broadband highly-efficient dielectric metadevices for polarization control

Nonlinear nanophotonics is a rapidly developing field of research with many potential applications for the design of nonlinear nanoantennas, light sources, nanolasers, and ultrafast miniature metadevices. A tight confinement of the local electromagnetic fields in resonant photonic nanostructures can boost nonlinear optical effects, thus offering versatile opportunities for the subwavelength control of light. To achieve the desired functionalities, it is essential to gain flexible control over the near- and far-field properties of nanostructures. To engineer nonlinear scattering from resonant nanoscale elements, both modal and multipolar control of the nonlinear response are widely exploited for enhancing the near-field interaction and optimizing the radiation directionality. Motivated by the recent progress of all-dielectric nanophotonics, where the electric and magnetic multipolar contributions may become comparable, here we review the advances in the recently emerged field of multipolar nonlinear nanophotonics, starting from earlier relevant studies of metallic and metal–dielectric structures supporting localized plasmonic resonances to then discussing the latest results for all-dielectric nanostructures driven by Mie-type multipolar resonances and optically induced magnetic response. These recent developments suggest intriguing opportunities for a design of nonlinear subwavelength light sources with reconfigurable radiation characteristics and engineering large effective optical nonlinearities at the nanoscale, which could have important implications for novel nonlinear photonic devices operating beyond the diffraction limit.

Multipolar nonlinear nanophotonics

The original Kerker effect was introduced for a hypothetical magnetic sphere, and initially it did not attract much attention due to a lack of magnetic materials required. Rejuvenated by the recent explosive development of the field of metamaterials and especially its core concept of optically-induced artificial magnetism, the Kerker effect has gained an unprecedented impetus and rapidly pervaded different branches of nanophotonics. At the same time, the concept behind the effect itself has also been significantly expanded and generalized. Here we review the physics and various manifestations of the generalized Kerker effects, including the progress in the emerging field of meta-optics that focuses on interferences of electromagnetic multipoles of different orders and origins. We discuss not only the scattering by individual particles and particle clusters, but also the manipulation of reflection, transmission, diffraction, and absorption for metalattices and metasurfaces, revealing how various optical phenomena observed recently are all ubiquitously related to the Kerker’s concept.

/pdf/generalized-kerker-effects-in-nanophotonics-and-meta-optics-3869p829ry.pdf

Generalized Kerker effects in nanophotonics and meta-optics [Invited]

A nanoantenna with balanced electric and magnetic dipole moments, known as the first Kerker condition, exhibits a directive radiation pattern with zero backscattering. In principle, a nanoantenna can provide even better directionality if higher order moments are properly balanced. Here, we study a generalized Kerker condition in the example of a nanoring nanoantenna supporting electric dipole and electric quadrupole moments. Nanoring antennas are well suited since both multipole moments can be almost independently tuned to meet the generalized Kerker condition.

/pdf/a-generalized-kerker-condition-for-highly-directive-cq4w3mqo2o.pdf

A generalized Kerker condition for highly directive nanoantennas

We study the angular scattering properties of individual core-shell nanoparticles that support simultaneously both electric and optically-induced magnetic resonances of different orders. In contrast to the approach to suppress the backward scattering and enhance the forward scattering relying on overlapping electric and magnetic dipoles, we reveal that the directionality of the forward scattering can be further improved through the interferences of higher order electric and magnetic modes. Since the major contributing electric and magnetic responses can be tuned to close magnitudes, ultra-directional forward scattering can be achieved by single nanoparticles without compromising the feature of backward scattering suppression, which may offer new opportunities for nanoantennas, photovoltaic devices, bio-sensing and many other interdisciplinary researches.

Ultra-directional forward scattering by individual core-shell nanoparticles.

Ultra-directional forward scattering by individual core-shell nanoparticles

The generation of vortex laser beam by using phase-only liquid crystal spatial light modulator (LC-SLM) combined with the spiral phase screen is experimentally and theoretically studied. Results show that Gaussian and dark hollow vortex laser beams can be generated by using this method successfully. Differing with the Gaussian and dark hollow beams, far field intensities of the generated vortex laser beams still exhibit dark hollow distributions. The comparisons between the ideal generation and experimental generation of vortex laser beams with different optical topological charges by using phase only LC-SLM is investigated in detail. Compared with the ideal generated vortex laser beam, phase distribution of the experimental generated vortex laser beam contains many phase singularities, the number of which is the same as that of the optical topological charges. The corresponding near field and far field dark hollow intensity distributions of the generated vortex laser beams exhibit discontinuous in rotational direction. Detailed theoretical analysis show that the main reason for the physical phenomenon mentioned above is the response error of phase only LC-SLM. These studies can provide effective guide for the generation of vortex laser beam by using phase only LC-SLM for optical tweezers and free space optical communication.

Study on the generation of a vortex laser beam by using phase-only liquid crystal spatial light modulator

The invention relates to an optical fiber laser collimating and shaping device and a design method thereof, which can be used for shaping light intensity of light beams output by an optical fiber laser device into required distribution, and can effectively compensate light beam phase change caused by light intensity shaping. The optical fiber laser collimating and shaping device adopts a double aspherical mirror structure, an aspherical mirror 1 is responsible for collimating and shaping light intensity of optical fiber laser, and further forming the required light intensity distribution at position of an aspherical mirror 2; and the aspherical mirror 2 1 is responsible for conducting phase compensation on the light beams after collimation and light intensity shaping, so that the light beams after shaping has the required light intensity distribution and has near-diffraction-limited phase distribution. The optical fiber laser collimating and shaping device integrates the light beam collimation, light intensity shaping and phase correction, and has the advantages of high shaping efficiency, convenient use and the like.

Wenke Xie

Papers

Ultra-directional forward scattering by individual core-shell nanoparticles.

Ultra-directional forward scattering by individual core-shell nanoparticles

Study on the generation of a vortex laser beam by using phase-only liquid crystal spatial light modulator

Optical fiber laser collimating and shaping device, and design method thereof

Adaptive beam shaping for improving the power coupling of a two-Cassegrain-telescope