Photonic Jet: Science and Application

Photonic jets (PJs) are important mesoscale optical phenomena arising from electromagnetic waves interacting with dielectric particles. PJs have applications in super-resolution imaging, sensing, detection, patterning, trapping, manipulation, waveguiding, signal amplification and high-efficiency signal collection, among others. This reprint provides an overview of the field and highlights recent advances and trends in PJ research

Nanopatterning with Photonic Nanojets: Review and Perspectives in Biomedical Research

: Nanostructured surfaces and devices offer astounding possibilities for biomedical research, including cellular and molecular biology, diagnostics, and therapeutics. However, the wide implementation of these systems is currently limited by the lack of cost-effective and easy-to-use nanopatterning tools. A promising solution is to use optical methods based on photonic nanojets, namely, needle-like beams featuring a nanometric width. In this review, we survey the physics, engineering strategies, and recent implementations of photonic nanojets for high-throughput generation of arbitrary nanopatterns, along with applications in optics, electronics, mechanics, and biosensing. An outlook of the potential impact of nanopatterning technologies based on photonic nanojets in several relevant biomedical areas is also provide

Bead Mediated Microscopy: from high resolution microscopy to nano-Raman

Solid-state physics, material science, as well as biology, need continuously more and more information from their samples. High spatial resolution information such as optical or electrical properties, chemical species identification as well as topography are important information that optical microscopy or Scanning Probe Microscopy (SPM) can provide. Although electron microscopy (SEM and TEM) certainly assumes a position of absolute importance in the field, its cost and its need to be used by highly specialised personnel still make it an instrument of limited everyday use. On the contrary, probe microscopy has now become of very high diffusion in research labs. To develop my thesis I focused myself on three main and somehow related microscopy techniques: high resolution Raman microscopy, Scanning Near-field Optical Microscopy (SNOM), and Tip Enhanced Raman Spectroscopy (TERS). All of them are state-of-the-art on surface optical analysis techniques but still present relevant limits; among others, respectively: spatial resolution, local power density, complexity and field of applicability. My approach wants to combine some aspects of these techniques to go beyond their limits. Raman spectroscopy is a powerful optical technique, which measures the inelastic scattering of an incoming EM radiation due to the vibrational modes of the molecules present on the surface of a sample. Thanks to its high specificity, it is very powerful in identifying the chemical components of a sample. Several organic and inorganic molecules have their typical Raman spectral peaks, hence, by the Raman spectra, it\u2019s possible to provide a qualitative and quantitative analysis of the elements of a sample. High spatial resolution Raman setups uses the combination of a confocal microscope with a spectrometer assisted by a series of long pass and band pass filters. Despite its extreme versatility, basing Raman spectroscopy on a confocal system also constrains it to acquire its limit in spatial resolution determined by the limit of diffraction. To overcome this limit the most used techniques in SPM are Scanning Near-field Optical Microscopy (SNOM) and Tip Enhanced Raman Spectroscopy (TERS). Both of them exploits evanescent field, which is an electric field that is created by oscillating charges and/or currents and does not propagate in the far field as a classical electromagnetic wave, but is spatially concentrated very near to its source. This confinement allows to obtain field sources definitely smaller than in confocal systems. In SNOM technique, the excitation light is focused through an aperture smaller than the wavelength, creating an evanescent field strongly localized near the aperture itself. Scanning the sample in this near range brings the spatial resolution down to the aperture dimension. The main disadvantage of aperture SNOM is that the overall optical efficiency of probes is very low. The excitation power cannot be too high in order to prevent any damage of the probe, hence the energy that reaches the sample is usually not enough for Raman analysis. TERS instead is more suitable for this purpose. It basically exploits Surface Enhanced Raman Spectroscopy (SERS) principles, using a laser irradiated gold sharp tip to obtain a local enhancement at its apex. Its good efficiency permits to analyze Raman effects with a spatial super-resolution, but, on the other hand, TERS probes usually lack of reprodubility and require very skilled and specialised users. My PhD project has been focused to investigate and optimize an original approach to perform high resolution optical microscopy and Raman spectroscopy, well below the diffraction limit. The concept is to exploit the optical proprieties of a dielectric micro bead lens to achieve a powerful nanoscale near field confinement of light and the Scanning Probe Microscopy (SPM) technique to scan a sample to acquire optical maps. When a dielectric micro bead is hit by an Electromagnetic (EM) wave its effect is to transmit and concentrate the incident EM radiation in a specific area called nanojet, at first glance similar to that created with a standard lens. Some optical proprieties of the nanojets have been already introduced in the literature, but their application in the world of SPM, their employment in Raman microscopy and their combination with nanostructures to improve the spatial resolution are novel features whose investigation is promising. I gave to this technique the name of Beam Mediated Microscopy (BeMM). The combination of super resolution bead mediated SPM with Raman spectroscopy opens interesting perspectives about powerful surface analysis for samples that need a versatile optical probe with a high spatial resolution and soft interaction with the sample, like soft matter substrates or biosamples

Surface roughness influence on photonic nanojet parameters of dielectric microspheres

Все природные и искусственно изготовленные твердые микрочастицы имеют шероховатую поверхность. При рассеянии на таких частицах оптического излучения текстура поверхности, помимо геометрической формы рассеивателя, становится важным морфологическим фактором, определяющим его оптические свойства. Мы представляем результаты численного FDTD-моделирования фокусировки оптической волны диэлектрической микросферой со случайно сгенерированными шероховатостями поверхности. Рассмотрены варианты азимутально симметричных и несимметричных искажений поверхности частицы. Показано, что ключевые параметры ближнепольной фокальной области (интенсивность, продольный и поперечные размеры, фокусное расстояние) для так называемой фотонной наноструи оказываются чувствительными к изменению текстуры поверхности сферы. При этом наибольшим изменениям подвержены два параметра – пиковая интенсивность фотонной наноструи и ее протяженность. Исследовано влияние оптического контраста (относительного показателя преломления) рассеивающей излучение микросферы на характеристики фотонной наноструи, а также показана возможность снижения влияния шероховатостей поверхности на качество фокусировки ближнего оптического поля при обводнении микросфер.Работа выполнена при поддержке Министерства науки и высшего образования в рамках выполнения работ по Государственному заданию ИОА СО РАН

Spectroscopic study of optical confinement and transport effects in coupled microspheres and pillar cavities

In this thesis we investigated the spatial and spectral mode profiles, and the optical transport properties of single and multiple coupled cavities. We performed numerical modeling of whispering gallery modes (WGMs) in such cavities in order to explain recent experiments on semiconductor micropillars. High quality (Q up to 20 000) WGMs with small mode volumes V ~0.3 µm3 in 4-5 µm micropillars were reproduced. The WGM spectra were found to be in a good agreement with the experimental data. The coupling between size-matched spheres from 2.9 to 6.0 µm in diameter was characterized using spectroscopy. We observed peculiar kites in the spectral images of such coherently coupled bispheres. The origin of these kites was explained due to the coupling of multiple pairs of azimuthal modes. We quantified the coupling constant for WGMs located in the equatorial plane of spheres parallel to the substrate which plays the most important role in the transport of WGMs in such structures. It was shown that in long (>10 spheres) chains of size-disordered polystyrene microspheres the transmission properties are dominated by photonic nanojet-induced modes (NIMs) leading to periodic focusing of light along the chain. In the transmission spectra of such chains we observed Fabry-Pe´rot fringes with propagation losses of only 0.08 dB per sphere at the maxima of the transmission peaks. The fringes of NIMs are found to be in a good agreement with the results of numerical modeling. These modes can be used in various biomedical applications requiring tight focusing of the beams

Dielectric-sphere-based microsystem for optical super-resolution imaging

Well-established imaging techniques proved that features below the diffraction limit can be observed optically using so-called super-resolution microscopies, which overcome Abbe's resolution limit. In traditional far-field microscopy, the introduction of fluorescent samples and engineered light paths was key for this breakthrough. In parallel, near-field techniques with similar performance were developed, but they suffered from a limited field-of-view. The merge of the two approaches was already demonstrated ~15 years ago, when micrometer-sized dielectric objects positioned on a sample were found to be able to image the sample with super-resolution. By observing the sample through the micro-object with a classical optical microscope, the latter could capture a virtual image showing sub-diffraction details. Although this way the near-field information transfer into the far-field by the micro-object was proven and found to be key for enabling super-resolution imaging, the limited field-of-view, as determined by the size of the micro-object, remained an issue. In this dissertation, a novel method is presented that provides a microscopy technique capable of achieving super-resolution without field-of-view restrictions. Based on previous studies, dielectric microspheres were chosen for this imaging technique. First, the working principle of these microspheres was explored by investigating both the illumination and the reflected light path. These findings provided a better understanding on the phenomena working behind microsphere-assisted imaging and allowed to create an engineering toolbox that can be used to design microsphere-based optical systems. This was followed by an investigation on microfabrication techniques, in order to create a microchip that can serve as a bridge between a single microsphere and the macro-sized-components of a classical optical microscope. The resulting chip was later embedded in a custom fixation system that allowed scanning of this microsphere over the sample, while keeping its position fixed compared to the microscope objective. The microscope mounted camera recorded pictures during the scan, which were used to generate a large field-of-view super-resolution image by stitching. After initial successes, the setup was improved in terms of robustness and application range. The new version allowed field-of-view in the millimeter range, while it could be operated in both oil- and water-immersion. Parallel imaging with an array of microspheres was also implemented, which further enhanced the imaging speed. The algorithmic background (including an automated scanning and image reconstruction protocol) of this microscopy method was developed in-house. Its validation showed superior performance compared to existing software. Future developments (e.g. employment of 3D-printing for mass-production, imaging in vivo biological samples, metrology applications) are envisioned. The findings presented here may pave the road for an easy-to-use, generalized super-resolution imaging system

Femtosecond Laser Joining of Silver Submicron/Nanoparticles

The development of future devices is towards to the miniaturization and performance improvement. This requires the large scale integration of nanodevices. Nanojoining is an essential step for the industrial scale production of nanodevices which possess extensive applications in nanoelectronics, nanophotonics and biomedicines. Many techniques have been developed to produce nanojoining, and among them femtosecond (fs) laser nanojoining is a promising one due to its limited thermal damage to the fabricated nanomaterials. However the fs laser nanojoining technique is still not probably characterized. In this thesis, the research of fs laser nanojoining of silver (Ag) nanomaterials with or without polyvinylpyrrolidone (PVP) coating is conducted in different environments (aqueous solution, air, vacuum), targeting to different application areas. It is reported that the joining behavior of PVP coated Ag nanoparticles (NPs) can be manipulated by controlling the distribution of localized surface plasmon induced electric field enhancement (or hotspots) and/or the decomposition of PVP coatings into amorphous carbon or some ionized products. This facilitates the fabrication of joined-NPs structures with tunable plasmonic properties by tuning the geometries of the structures, for possible application as SERS (surface enhanced Raman spectroscopy) detector. For Ag particles without PVP coating and exposed to vacuum (10-6 Torr), their joining behavior under fs laser radiation is also controlled by the hotspots; and high integrity interconnection of Ag particles can be obtained benefiting from the localized ablation of the particles in the hotspots. The joining efficiency can be improved by introducing reactive oxygen gas which produces external heating to the irradiated particles through O Ag reaction on the surface of Ag particles in the hotspots. Overall, the hotspots-dependent fs laser nanojoining technique which is developed in this research provides an alternative way for precise fabrication of nanodevices based on the interconnection of nanoscale functional components

NIAC Phase II Orbiting Rainbows: Future Space Imaging with Granular Systems

Inspired by the light scattering and focusing properties of distributed optical assemblies in Nature, such as rainbows and aerosols, and by recent laboratory successes in optical trapping and manipulation, we propose a unique combination of space optics and autonomous robotic system technology, to enable a new vision of space system architecture with applications to ultra-lightweight space optics and, ultimately, in-situ space system fabrication. Typically, the cost of an optical system is driven by the size and mass of the primary aperture. The ideal system is a cloud of spatially disordered dust-like objects that can be optically manipulated: it is highly reconfigurable, fault-tolerant, and allows very large aperture sizes at low cost. This new concept is based on recent understandings in the physics of optical manipulation of small particles in the laboratory and the engineering of distributed ensembles of spacecraft swarms to shape an orbiting cloud of micron-sized objects. In the same way that optical tweezers have revolutionized micro- and nano-manipulation of objects, our breakthrough concept will enable new large scale NASA mission applications and develop new technology in the areas of Astrophysical Imaging Systems and Remote Sensing because the cloud can operate as an adaptive optical imaging sensor. While achieving the feasibility of constructing one single aperture out of the cloud is the main topic of this work, it is clear that multiple orbiting aerosol lenses could also combine their power to synthesize a much larger aperture in space to enable challenging goals such as exo-planet detection. Furthermore, this effort could establish feasibility of key issues related to material properties, remote manipulation, and autonomy characteristics of cloud in orbit. There are several types of endeavors (science missions) that could be enabled by this type of approach, i.e. it can enable new astrophysical imaging systems, exo-planet search, large apertures allow for unprecedented high resolution to discern continents and important features of other planets, hyperspectral imaging, adaptive systems, spectroscopy imaging through limb, and stable optical systems from Lagrange-points. Furthermore, future micro-miniaturization might hold promise of a further extension of our dust aperture concept to other more exciting smart dust concepts with other associated capabilities. Our objective in Phase II was to experimentally and numerically investigate how to optically manipulate and maintain the shape of an orbiting cloud of dust-like matter so that it can function as an adaptable ultra-lightweight surface. Our solution is based on the aperture being an engineered granular medium, instead of a conventional monolithic aperture. This allows building of apertures at a reduced cost, enables extremely fault-tolerant apertures that cannot otherwise be made, and directly enables classes of missions for exoplanet detection based on Fourier spectroscopy with tight angular resolution and innovative radar systems for remote sensing. In this task, we have examined the advanced feasibility of a crosscutting concept that contributes new technological approaches for space imaging systems, autonomous systems, and space applications of optical manipulation. The proposed investigation has matured the concept that we started in Phase I to TRL 3, identifying technology gaps and candidate system architectures for the space-borne cloud as an aperture