Optomechanical manipulation with hyperbolic metasurfaces

Auxiliary nanostructures introduce additional flexibility into optomechanical manipulation schemes. Metamaterials and metasurfaces capable to control electromagnetic interactions at the near-field regions are especially beneficial for achieving improved spatial localization of particles, reducing laser powers required for trapping, and for tailoring directivity of optical forces. Here, optical forces acting on small particles situated next to anisotropic substrates, are investigated. A special class of hyperbolic metasurfaces is considered in details and is shown to be beneficial for achieving strong optical pulling forces in a broad spectral range. Spectral decomposition of the Green functions enables identifying contributions of different interaction channels and underlines the importance of the hyperbolic dispersion regime, which plays the key role in optomechanical interactions. Homogenised model of the hyperbolic metasurface is compared to its metal-dielectric multilayer realizations and is shown to predict the optomechanical behaviour under certain conditions related to composition of the top layer of the structure and its periodicity. Optomechanical metasurfaces open a venue for future fundamental investigations and a range of practical applications, where accurate control over mechanical motion of small objects is required

Phenological shifts of abiotic events, producers and consumers across a continent

Ongoing climate change can shift organism phenology in ways that vary depending on species, habitats and climate factors studied. To probe for large-scale patterns in associated phenological change, we use 70,709 observations from six decades of systematic monitoring across the former Union of Soviet Socialist Republics. Among 110 phenological events related to plants, birds, insects, amphibians and fungi, we find a mosaic of change, defying simple predictions of earlier springs, later autumns and stronger changes at higher latitudes and elevations. Site mean temperature emerged as a strong predictor of local phenology, but the magnitude and direction of change varied with trophic level and the relative timing of an event. Beyond temperature-associated variation, we uncover high variation among both sites and years, with some sites being characterized by disproportionately long seasons and others by short ones. Our findings emphasize concerns regarding ecosystem integrity and highlight the difficulty of predicting climate change outcomes. The authors use systematic monitoring across the former USSR to investigate phenological changes across taxa. The long-term mean temperature of a site emerged as a strong predictor of phenological change, with further imprints of trophic level, event timing, site, year and biotic interactions.Peer reviewe

Chronicles of nature calendar, a long-term and large-scale multitaxon database on phenology

We present an extensive, large-scale, long-term and multitaxon database on phenological and climatic variation, involving 506,186 observation dates acquired in 471 localities in Russian Federation, Ukraine, Uzbekistan, Belarus and Kyrgyzstan. The data cover the period 1890-2018, with 96% of the data being from 1960 onwards. The database is rich in plants, birds and climatic events, but also includes insects, amphibians, reptiles and fungi. The database includes multiple events per species, such as the onset days of leaf unfolding and leaf fall for plants, and the days for first spring and last autumn occurrences for birds. The data were acquired using standardized methods by permanent staff of national parks and nature reserves (87% of the data) and members of a phenological observation network (13% of the data). The database is valuable for exploring how species respond in their phenology to climate change. Large-scale analyses of spatial variation in phenological response can help to better predict the consequences of species and community responses to climate change.Peer reviewe

Optical Pulling Forces In Hyperbolic Metamaterials

Control over mechanical motion of nanoscale particles is a valuable functionality desired in a variety of multidisciplinary applications, e.g., biophysics, and it is usually achieved by employing optical forces. Hyperbolic metamaterials enable tailoring and enhancing electromagnetic scattering and, as the result, provide a platform for a new type of optical manipulation. Here optical pulling forces acting on a small particle placed inside a hyperbolic metamaterial slab were predicted and analyzed. In order to attract particles to a light source, highly confined extraordinary modes of hyperbolic metamaterial were excited via scattering from an imperfection situated at the slab\u27s interface. This type of structured illumination together with remarkable scattering properties, inspired by the hyperbolic dispersion in the metamaterial, creates optical attraction. Forces acting on high-, low-index dielectric, and gold particles were investigated and it was shown that the pulling effect emerges in all of the cases. The ability to control mechanical motion at nanoscale using auxiliary photonic structures paves the way for investigation of various phenomena, e.g., biochemical reactions, molecular dynamics, and more

Optical binding via surface plasmon polariton interference

[EN] Optical binding allows creation of mechanically stable nanoparticle configurations owing to formation of self-consistent optical trapping potentials. While the classical diffraction limit prevents achieving deeply subwavelength arrangements, auxiliary nanostructures enable tailoring optical forces via additional interaction channels. Here, a dimer configuration next to a metal surface was analyzed in detail and the contribution of surface plasmon polariton waves was found to govern the interaction dynamics. It is shown that the interaction channel, mediated by resonant surface waves, enables achieving subwavelength stable dimers. Furthermore, the vectorial structure of surface modes allows binding between two dipole nanoparticles along the direction of their dipole moments, contrary to vacuum binding, where a stable configuration is formed in the direction perpendicular to the polarization of the dipole moments. In addition, the enhancement by one order of magnitude of the optical binding stiffness is predicted owing to the surface plasmon polariton interaction channel. These phenomena pave the way for developing new flexible optical manipulators, allowing for control over a nanoparticle trajectory on subwavelength scales and opening opportunities for optical-induced anisotropic (i.e., with different periods along the field polarization as well as perpendicular to it) organization of particles on a plasmonic substrate.The authors acknowledge the support of the Russian Foundation for Basic Research (Grants No. 16-32-60167, No. 18-02-00414, No. 18-29-20063, and No. 18-52-00005). M.I.P. also acknowledges the support from the BASIS Foundation. A.S. acknowledges the support of the Ministry of Education and Science of the Russian Federation (GOSZADANIE, Grant No. 3.4982.2017/6.7). The force calculations were partially supported by Russian Science Foundation (Grant No. 18-72-10127). M.N.-V. is supported by the Spanish MINECO Grants No. FIS2012-36113-C03-03, No. FIS2014-55563-REDC, and No. FIS2015-69295-C3-1-P