arXiv subjects

Augustine M. Urbas

Publications and source records attributed to Augustine M. Urbas.

9 recordsLinked to original sources

arXiv2023

All-glass 100 mm Diameter Visible Metalens for Imaging the Cosmos

Metasurfaces, optics made from subwavelength-scale nanostructures, have been limited to millimeter-sizes by the scaling challenge of producing vast numbers of precisely engineered elements over a large area. In this study, we demonstrate an all-glass 100 mm diameter metasurface lens (metalens) comprising 18.7 billion nanostructures that operates in the visible spectrum with a fast f-number (f/1.5, NA=0.32) using deep-ultraviolet (DUV) projection lithography. Our work overcomes the exposure area constraints of lithography tools and demonstrates that large metasurfaces are commercially feasible. Additionally, we investigate the impact of various fabrication errors on the imaging quality of the metalens, several of which are unique to such large area metasurfaces. We demonstrate direct astronomical imaging of the Sun, the Moon, and emission nebulae at visible wavelengths and validate the robustness of such metasurfaces under extreme environmental thermal swings for space applications.

physics.optics↗

arXiv2018

Saddle point singularity and optical phase transition in bilayer hyperbolic metamaterials

We study theoretically and numerically high density of states for hyperbolic bilayered metamaterials (HMM). It reveals that density response of HMM is reminiscent of Fermi electronic band structure of metal or semiconductors. By the method of Green function a van Hove type singularity is found in photonic density spectra of HMM with saddle point localization on photonic Fermi surface (FS) of metamaterial. Similar to the electronic systems, the photonic FS experiences instabilities induced by the changes in volume fractions of its constituents that leads to the Lifshitz type zero-temperature phase transition between FS of types I and II hyperbolic states at the topology protected critical point.

physics.app-ph↗

arXiv2016

Surface plasmon amplification by stimulated emission of radiation in hyperbolic metamaterials

We study theoretically and numerically spasing conditions and optical dynamics of a composite hyperbolic metamaterial interacting with gain molecules. By combining Maxwell-Bloch equations with Green's function approach, we calculate lasing frequency and threshold population inversion for various gain density in the gain layer. We demonstrate high level of enhancement for photonic density of states in spacious spectral range provided by hyperbolic metastructures. We find that direct dipole-dipole interactions between molecules in the gain layer has a negligible effect on spasing conditions. We identify a region of parameters in which spasing can occur considering these effects.

cond-mat.mes-hall↗

arXiv2016

Label-Free Nanoscopy with Contact Microlenses: Super-Resolution Mechanisms and Limitations

Despite all the success with developing super-resolution imaging techniques, the Abbe limit poses a severe fundamental restriction on the resolution of far-field imaging systems based on diffraction of light. Imaging with contact microlenses, such as microspheres or microfibers, can increase the resolution by a factor of two beyond the Abbe limit. The theoretical mechanisms of these methods are debated in the literature. In this work, we focus on the recently expressed idea that optical coupling between closely spaced nanoscale objects can lead to the formation of the modes that drastically impact the imaging properties. These coupling effects emerge in nanoplasmonic or nanocavity clusters, photonic molecules, or various arrays under resonant excitation conditions. The coherent nature of imaging processes is key to understanding their physical mechanisms. We used a cluster of point dipoles, as a simple model system, to study and compare the consequences of coherent and incoherent imaging. Using finite difference time domain modeling, we show that the coherent images are full of artefacts. The out-of-phase oscillations produce zero-intensity points that can be observed with practically unlimited resolution (determined by the noise). We showed that depending on the phase distribution, the nanoplasmonic cluster can appear with the arbitrary shape, and such images were obtained experimentally.

physics.optics↗

arXiv2016

Coulomb and quenching effects in small nanoparticle-based spasers

We study numerically the effect of mode mixing and direct dipole-dipole interactions between gain molecules on spasing in a small composite nanoparticles with a metallic core and a dye-doped dielectric shell. By combining Maxwell-Bloch equations with Green's function formalism, we calculate lasing frequency and threshold population inversion for various gain densities in the shell. We find that gain coupling to nonresonant plasmon modes has a negligible effect on spasing threshold. In contrast, the direct dipole-dipole coupling, by causing random shifts of gain molecules' excitation frequencies, hinders reaching the spasing threshold in small systems. We identify a region of parameter space in which spasing can occur considering these effects.

cond-mat.mes-hall↗

arXiv2015

Movable thin films with embedded high-index microspheres for super-resolution microscopy

Microsphere-assisted imaging emerged as a surprisingly simple way of achieving optical super-resolution imaging. In this work, we use movable PDMS thin films with embedded high-index barium titanate glass microspheres a sample scanning capability was developed, thus removing the main limitation of this technology based on its small field-of-view.

physics.optics↗

arXiv2015

Spectrally resolved resonant propulsion of dielectric microspheres

Use of resonant light forces opens up a unique approach to high-volume sorting of microspherical resonators with much higher uniformity of resonances compared to that in coupled-cavity structures obtained by the best semiconductor technologies. In this work, the spectral response of the propulsion forces exerted on polystyrene microspheres near tapered microfibers is directly observed. The measurements are based on the control of the detuning between the tunable laser and internal resonances in each sphere with accuracy higher than the width of the resonances. The measured spectral shape of the propulsion forces correlates well with the whispering-gallery mode resonances in the microspheres. The existence of a stable radial trap for the microspheres propelled along the taper is demonstrated. The giant force peaks observed for 20-μm spheres are found to be in a good agreement with a model calculation demonstrating an efficient use of the light momentum for propelling the microspheres.

physics.optics↗

arXiv2014

Super-Resolution Imaging by Arrays of High-Index Spheres Embedded in Transparent Matrices

We fabricated thin-films made from polydimethylsiloxane (PDMS) with embedded high-index (n~1.9-2.2) microspheres for super-resolution imaging applications. To control the position of microspheres, such films can be translated along the surface of the nanoplasmonic structure to be imaged. Microsphere-assisted imaging, through these matrices, provided lateral resolution of ~λ/7 in nanoplasmonic dimer arrays with an illuminating wavelength λ=405 nm. Such thin films can be used as contact optical components to boost the resolution capability of conventional microscopes.

physics.optics↗

arXiv2013

Cooperative amplification of energy transfer in plasmonic systems

We study cooperative effects in energy transfer (ET) from an ensemble of donors to an acceptor near a plasmonic nanostructure. We demonstrate that in cooperative regime ET takes place from plasmonic superradiant and subradiant states rather than from individual donors leading to a significant increase of ET efficiency. The cooperative amplification of ET relies on the large coupling of superradiant states to external fields and on the slow decay rate of subradiant states. We show that superradiant and subradiant ET mechanisms are efficient in different energy domains and therefore can be utilized independently. We present numerical results demonstrating the amplification effect for a layer of donors and an acceptor on a spherical plasmonic nanoparticle.

cond-mat.mes-hall↗