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Simultaneous field- and aperture-plane (back-focal plane, BFP) imaging enriches the information content of fluorescence microscopy. In addition to the usual density and concentration maps of sample-plane images, BFP images provide information on the surface proximity and orientation of molecular fluorophores. They also give access to the refractive index of the fluorophore-embedding medium. However, in the high-NA, wide-field detection geometry commonly used in single-molecule localisation microscopies, such measurements are averaged over all fluorophores present in the objective’s field of view, thus limiting spatial resolution and specificity. We here solve this problem and demonstrate how an oblique, variable-angle, coherent ring illumination can be used to generate a Bessel beam that - for supercritical excitation angles - produces an evanescent needle of light. Scanning the sample through the this evanescent needle enables us to acquire combined sample-plane and BFP images with sub-diffraction resolution and axial localisation precision. Background, resolution and polarisation considerations will be discussed.

We present two distinct types of ‘smart’ surfaces designed for facilitating the quantitative exploration of dynamic processes occurring at sub-wavelength distances from interfaces, using far-field optical techniques. Based on evanescent waves in excitation and/or emission, we achieve an axial localization precision of about 10 nm. The first type of substrate incorporates nanocavities in a thin metallic film, enhancing and confining the electromagnetic field to a tiny volume. The second sample consists of a thin fluorescent film sandwiched between transparent spacer and capping layers deposited on a glass coverslip. The emission pattern from this film codes detailed information about the local fluorophore environment, namely, the refractive index, defects, reciprocal lattice, and the axial distance of the molecular emitter from the surface. An application to axial metrology in total internal reflection fluorescence and axial super-localisation microscopes is presented.

Emission patterns from molecules at interfaces encode many details about their local environment and their axial position, along the microscope’s optical axis. We introduce an advanced approach that synergizes back focal plane (BFP) imaging with innovative ‘smart’ surfaces make surface imaging more qualitative, more reliable, and more robust. Our method is particularly focused on accurately measuring the refractive index (RI) of transparent thin films and their imperfections close to the interfaces. Our technique utilizes a ‘smart’ surface, which features a uniform fluorescent thin film of about 4 nm thickness together with back-focal plane (BFP) imaging. We manage to detect bubbles or other imperfection in 100 nm thin film of polymer with RI of 1.34.

Localized surface plasmon resonances of individual sub-wavelength cavities milled in metallic films can couple to each other to form a collective behavior. This coupling leads to a delocalization of the plasmon field at the film surface and drastically alters both the linear and nonlinear optical properties of the sample. In periodic arrays of nanocavities, the coupling results in the formation of propagating surface plasmon polaritons (SPP), eigenmodes extending across the array. When artificially introducing dislocations, defects and imperfections, multiple scattering of these SPP modes can lead to hot-spot formation, intense and spatially confined fluctuations of the local plasmonic field within the array. Here, we study the underlying coupling effects by probing plasmonic modes in well-defined individual triangular dimer cavities and in arrays of triangular cavities with and without artificial defects. Nonlinear confocal spectro-microscopy is employed to map the second harmonic (SH) radiation from these systems. Pronounced spatial localization of the SPP field and significant enhancements of the SH intensity in certain, randomly distributed hot spots by more than an order of magnitude are observed from the triangular arrays as compared to a bare silver film by introducing a finite degree of disorder into the array structure. Hot-spot formation and the resulting enhancement of the nonlinear efficiency are correlated with an increase in the lifetime of the localized SPP modes. By using interferometric SH autocorrelation measurements, we reveal lifetimes of hot-spot resonances in disordered arrays that are much longer than the few-femtosecond lifetimes of the localized surface plasmon resonances of individual nanocavity dimers. This suggests that hot spot lifetime engineering provides a path for manipulating the linear and nonlinear optical properties of nanosystems by jointly exploiting coherent couplings and tailored disorder.

We investigated the formation of nanoporous metallic networks through a physical vapor deposition (PVD) process. Utilizing transmission electron microscopy (TEM), we observe the early stages of growth, revealing the presence of large pores and pillars. Our findings highlight the significant influence of the electrostatic nature of the substrate on the metallic network growth, where repulsion and attraction mechanisms come into play during the deposition process. We extend the applicability of this method, demonstrating its versatility in fabricating macroscopic metallic networks composed of submicrometer building blocks on different substrates, among them an amber stone, in a one-step process. The resulting three-dimensional (3D) networks display distinctive nonlinear optical properties, including enhanced second harmonic generation (SHG) and surface-enhanced Raman scattering (SERS) responses. The latter is used to detect contamination in water down to 10–8 M. [ABSTRACT FROM AUTHOR]

Samples of H6TPPS J aggregates and bundles, deposited on glass and aligned under nitrogen flow, were measured in a 2-photon microscopy setup. Changes in the polarization state of the incoming laser have shown a difference in the resulting 2-photon scanning of the same measured sample, revelling otherwise hidden features. In addition, tracing the response of certain areas under different polarisation can provide information about the arrangement of the dipoles in that area. This shows the significant role of polarisation in 2-photon measurement, and the need to consider such effects in the microscopy of biological samples.

Confocal microscopes have been the workhorses of 3-D biological imaging, but they are slow, offer limited depth penetration and collect only ballistic photons. With their inefficient use of excitation photons they expose biological samples to an often intolerably high light burden. The speed limitation and photo-bleaching risk can be somewhat relaxed in a spinning-disk geometry, due to shorter pixel dwell times and rapid re-scans during image capture. Alternatively, light-sheet microscopes rapidly image large volumes of transparent or chemically cleared samples. Finally, with infrared excitation and efficient scattered-light collection, 2-photon microscopy allows deep-tissue imaging, but it remains slow. Here, we describe a new optical scheme that borrows the best from three different worlds: the speed and direct-view from a spinning-disk confocal, deep tissue-penetration and intrinsic optical sectioning from 2-photon excitation, and a large field of view and a low invasiveness of a selective-plane illumination microscope – all with a single objective lens. We validate the performance of our 2-photon spinning-disk microscope in various applications that have in common to simultaneously require a large depth penetration, high speed and larger fields of view. Beyond biological fluorescence, we demonstrate an application in material science, imaging coherent non-linear scattering from a 3-D nano-porous network.

Second harmonic generation (SHG) is forbidden for centrosymmetric materials such metals. Yet, symmetry can be broken by introducing plasmonic nano-structures which lead to enhancement of the electromagnetic field at both the fundamental and the SH frequencies. Using non-linear microscopy, we experimentally demonstrate enhanced SHG from isosceles triangular cavities (~215 nm side length, 200 nm base) milled in thin aluminum film. Upon strong interaction between the cavities, they behave as a single unit and response in a coherent manner, i.e. SHG is observed from the coupled system. The hybridization between the cavities is not only dependent on the distance between them, but their spatial arrangement is found to be a crucial parameter. That is, the SHG efficiency can be enhanced upon different arrangement of the same cavities, holding the same distance between them. We characterize those cavities also by cathodoluminescence and show that the structure support plasmonic modes both at the fundamental and the SH frequencies.

Total internal reflection fluorescence (TIRF) has come of age, but a reliable and easy-to-use tool for calibrating evanescent-wave penetration depths is missing. We provide a test-sample for TIRF and other axial super-resolution microscopies for emitter axial calibration. Our originality is that nanometer(nm) distances along the microscope’s optical axis are color-encoded in the form of a multi-layered multi-colored transparent sandwich. Emitter layers are excited by the same laser but they emit in different colors. Layers are deposited in a controlled manner onto a glass substrate and protected with a non-fluorescent polymer. Decoding the penetration depth of the exciting evanescent field, by spectrally unmixing of multi-colored samples is presented as well. Our slide can serve as a test sample for quantifying TIRF, but also as an axial ruler for nm-axial distance measurements in single-molecule localization microscopies, supercritical-angle fluorescence, and related super-resolution.

Nanoporous metallic systems exhibit a new generation of advanced materials with potential in a wide variety of technological fields among them catalysis, photonics, optoelectronics and sensors.Their high surface-to-volume ratio, multimodal nanoscale moieties, ability to host guest materials, and inhomogeneous surface at the submicron scale distinct them from both bulk metals and conventional plasmonic materials as well as meta-surfaces. Those structures can be prepared through different fabrication and synthesis strategies including chemical dealloying, assembly of pre-synthesized metallic nanoparticles, and via templating. In a sharp contrast with these preparation strategies, we have demonstrated one can fabricate a macroscopic nanopourus metallic networks by using physical vapor deposition in a short single-step process. These materials are highly pure, and they show very unique linear and non-linear optical properties, among them high Second-Harmonic-generation response. Herein, we will discuss their growth process mechanism, and utilize it for more complex 3d structure which behave as SHG reflectors.

Metamaterials and plasmonic structures made from aluminum (Al) have attracted significant interest due to their low cost, long-term stability, and the relative abundance of aluminum compared to the rare metals. Also, aluminum displays distinct dielectric properties allowing for the excitation of surface plasmons in the ultraviolet region with minimal non-radiative losses. Despite these clear advantages, most of the research has been focused on either gold or silver, probably due to difficulties in forming smooth thin films of aluminum. In the present work, we detect and characterize second harmonic generation (SHG) in the optical regime, emanating from triangular hole arrays milled into thin aluminum films in reflection mode, at normal incidence. We report intense nonlinear responses, year-long stability, and overall superior performances with respect to gold. The robustness of the Al structures and high reproducibility of the measured SHG responses allowed us to investigate changes in the directional emission upon tiny modifications in the structure's symmetry. We also demonstrate large-field instantaneous SHG imaging over areas containing several hole arrays using a recent, non-linear single-spinning disk microscope. Such high spatio-temporal resolution imaging has important applications, e.g., when studying chemical transformations occurring at electrode surfaces during charging and discharging cycles, as well as ageing. [ABSTRACT FROM AUTHOR]

Disordered metallic nanostructures have features that are not realized in well‐defined nanometallic counterparts, such as broadband light localization and inhomogeneous refraction index at the nanoscale. Disordered metal systems with a networked inner architecture have both particles and voids with subwavelength dimensions which are randomly 3D organized in space. These disordered structures are benefited from high surface area and damage stability, permit guest materials permeability, and can be achieved in large scales employing less costs and expertise. Their abundant nanosize gaps and sharp tips can interact with incident light over a broadband range to generate a rich pattern of hot‐spots and can therefore function as an artificial leaf, for example. Here, the linear and nonlinear optical properties of both well‐defined and disordered plasmonic structures are reviewed with a focus on largescale 3D metallic networks. An efficiency comparison of those structures as an optical source for second harmonic generation is presented as well. [ABSTRACT FROM AUTHOR]

An investigation on monolayers of alkyl chains, attached through direct Si-C bonds to Si(111), through phosphonates to GaAs(100) surfaces, or deposited as alkyl-silane monolayers on SiO2 is conducted by ultraviolet and inverse photoemission spectroscopy and X-ray absorption spectroscopy. Exposure to ultraviolet radiation from a He discharge lamp, or to a beam of energetic electrons, leads to significant damage, presumably associated with radiation- or electron-induced H-abstraction leading to carbon-carbon double-bond formation in the alkyl monolayer.

The direct chemical synthesis of coloidal Co2+: TiO2 nanocrystals and the use of these nanocrystals for the preparation of thin films showing very strong room temperature ferromagnetism. It was concluded that very stron room temperature ferromagnetism can be obtained by processing nomogenous colloidal Co2+:TiO2 nanocrystals under aerobic conditions that preclude the formation of metallic cobalt.

The effect of the presence or absence of chemical bonds between alkyl chain monolayers and the contacts in metal/molecule/semiconductor junctions on the current-voltage characteristics is studied. The result suggests that small geometrical defects produced by relatively low pressures are sufficient to make substantial changes in the electrical behavior of alkyl chains.