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The optical-based super-resolution, non-invasive method is preferred for the inspection of surfaces with massive microstructures widely applied in functional surfaces. The Structured Illumination Microscopy (SIM) uses standing-wave illumination to reach optical super-resolution. Recently, coherent SIM is being studied. It can obtain both the super-resolved intensity distribution and the phase and amplitude distribution from the sample surface. By analysis of the phase-depth dependency, the depth measurement for microgroove structures with coherent SIM is expected. FDTD analysis is applied for observing the near-field response of microgroove narrower than the diffraction limit under the standing-wave illumination. The near-field phase shows depth dependency in this analysis.

Photonic spin-orbit interaction has attracted much attention in recent years. This talk first reports the efficient generation of ultra-compact optical vortex (OV) in achiral nanostructures, which has a radius of only 1 μm and possesses a signal-to-noise ratio larger than 6 dB. A spin-selective and phase-resolved scanning near-field optical microscope (SNOM) is employed to probe and visualize the OV generation process in the spin basis. Furthermore, a SNOM system is developed for probing and analyzing nonlinear optical signals in nanostructures with subwavelength resolution, which images the near-field third-harmonic generation from an anapole dark-mode state in a silicon nanodisk.

We study the modification of fluorescence emission and decay rate of single fluorescent molecules in the near field of a periodic plasmonic nanostructure formed by a square lattice of Au hollow conical pillars with a periodicity of 250 nm. We perform nanometer-resolved imaging of the LDOS by simultaneously mapping the position and the decay rate of photoactivatable single-molecules with a novel super-resolved microscopy approach which enables multiplexed and super-resolved fluorescence lifetime imaging at the single-molecule level (smFLIM) with a field of view of ~10 µm2. We observe the LDOS modification of such optically rich material at different illumination conditions and we measure a large Purcell factor enhancement which increases for oblique illumination of the nanostructure.

Topologically tailored photonic crystals offer robust transport of optical states in quantum and classical systems. However, quantifying the robustness of edge states in topologically protected PhCs has remained elusive. In our recent work, we report a rigorous quantitative evaluation of topological photonic edge eigenstates, emulating the quantum valley Hall effect (VPC), and analyze their transport properties in the telecom wavelength range using a phase-resolved near-field optical microscope. Our results demonstrate that the backscattering energy ratio for the VPC is two orders of magnitude smaller compared to that in a conventional W1 waveguide. Such an evaluation opens a pathway for creating quantum photonic networks that can achieve secure and robust communications.

With the development of integrated circuits, MEMS devices and biotechnology, people are demanding more and more for the detection of complex micro-structures. The diffraction limit of light restricts the resolution of traditional optical microscopes. Near-field optical microscopes can avoid Rayleigh criterion and break through the diffraction limit by detecting the details of objects with evanescent waves to achieve super resolution measurement. The minimum resolution of 60nm can be achieved by balancing the light throughout and aperture size of the aperture SNOM. While, the resolution of the scattering SNOM depends on the curvature radius of the tip of the probe. The resolution below 20nm can be obtained, but the signal can be extracted by a composite interference optical system and phase-locked technology. People have continued to pursue the development of near-field optical microscope with more convenient, more reliable and smaller resolution. In this paper, a surface plasmon probe with the combination of aperture and scattering is presented. The structure is shown in the attached drawings. On the basis of a commercial AFM probe, a composite probe based on the combination of surface plasmon enhancement and scattering probe focusing was formed by coating SiO 2 probe and etching a single ring. The structure of the probe was optimized, in order to achieve larger enhancement of the light field. Furthermore, the combination of aperture SNOM illumination can greatly suppress background noise and achieve higher signal-to-noise ratio. By these two technologies, interference optical system and phase-locked technology can be avoided, thus simplifying the design of SNOM instruments. The finite-difference time-domain method is utilized to simulate and calculate the field distribution of the focusing spot and optimize the microstructure of the excited surface plasmon, which provides a strong theoretical support for the probe fabrication.

The single-beam gradient force optical tweezers have transformed various fields of scientific research by enabling manipulation and characterization of single molecules. Conventional optical tweezers pose limitations in trapping particles in the sub-Rayleigh regime. These limitations have been overcome with the help of plasmonic nanoapertures like the double-nanohole aperture. A modified colloidal lithography technique has been used in fabrication of double-nanohole apertures achieving dimensions appropriate for trapping single molecules in this regime. This paper demonstrates optical trapping of a single 10 nm enzyme, rubisco, using double-nanohole apertures fabricated using the modified colloidal lithography technique as well as presents the results from transmission characterization of different double-nanohole apertures carried out using the finite-difference time-domain (FDTD) simulations.

The effective optical constants of fishnet metamaterial are affected by the surrounding dielectric material or layers Analytical formulas were derived to retrieve the effective optical constants of fishnet metamaterial surrounded by different bulk materials, from reflection and transmission coefficients, and the effective optical constants of the fishnet embedded in thin film layers stack were retrieved numerically. With increase of the refractive index of the surrounding dielectric material as well as of the thickness of the nearby dielectric layers, the plasmonic resonance spectral position undergoes redshift while the absolute maximum value of negative refractive index of fishnet decreases.

Near-field imaging techniques at terahertz (THz) frequencies are severely restricted by diffraction. To date, different detection schemes have been developed, based either on sub-wavelength metallic apertures or on sharp metallic tips. However high-resolution THz imaging, so far, has been relying predominantly on detection techniques that require either an ultrafast laser or a cryogenically-cooled THz detector, at the expenses of a lack of sensitivity when high resolution levels are needed. Here, we demonstrate two novel near-field THz imaging techniques able to combine strongly sub-wavelength spatial resolution with highly sensitive amplitude and phase detection capability. The first technique exploits an interferometric optical setup based on a THz quantum cascade laser (QCL) and on a near-field probe nanodetector, operating at room temperature. By performing phase-sensitive imaging of THz intensity patterns we demonstrate the potential of our novel architecture for coherent imaging with sub-wavelength spatial resolution improved up to 17 ?m. The second technique is a detector-less s-SNOM system, exploiting a THz QCL as source and detector simultaneously. This approach enables amplitude- A nd phase-sensitive imaging by self-mixing interferometry with spatial resolution of 60-70 nm.

At the German Aerospace Center in Stuttgart a laser damage test bench is run to evaluate damage thresholds of various optical components. The system setup is based on the current ISO standards 11254 for single shot and multiple pulse operation. The laser damage test bench contains two repetitively pulsed laser sources, a Ti:Sapphire and a Nd:YAG laser, operating at wavelengths of 775 nm and 1064 nm, respectively. Harmonic wavelength converters to the visible spectral range are available. Both lasers are supplying the same damage testing rig. Online damage assessment techniques like sensitive scatter probe monitoring and video microscopy monitoring are used. The system is suited and has been tested extensively in the past for dielectric coated optics like beam turning mirrors, reflectors and windows, nonlinear optical components, semiconductors, and laser crystals. The damage test bench is located in a class 10,000 cleanroom environment under a laminar flowbox providing an additional isolation factor of >10^3. The tests can also be performed in sealed optical compartments in partial vacuum and under long term irradiation conditions. All experiments are supported by theoretical simulation of laser-material interactions, down to the sub-ps timescale.

In October 2013 the Lunar Laser Communications Demonstration (LLCD) made communications history by successfully demonstrating 622 megabits per second laser communication from the moon’s orbit to earth. The LLCD consisted of the Lunar Laser Communication Space Terminal (LLST), developed by MIT Lincoln Laboratory, mounted on NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft and a primary ground terminal located in New Mexico, the Lunar Laser Communications Ground Terminal (LLGT), and two alternate ground terminals. This paper presents the optical layout of the LLST, the approach for testing the optical subsystems, and the results of the optical qualification of the LLST. Also described is the optical test set used to qualify the LLST. The architecture philosophy for the optics was to keep a small, simple optical backend that provided excellent boresighting and high isolation between the optical paths, high quality wavefront on axis, with minimal throughput losses on all paths. The front end large optics consisted of a Cassegrain 107mm telescope with an f/0.7 parabolic primary mirror and a solar window to reduce the thermal load on the telescope and to minimize background light received at the sensors.

In this work, nanolithographic patterning by means of a nanostencil inscribed on an optical fiber tip is presented. Oneshot registration of multiple-sized features within a 4 μm diameter patterning circle has been experimentally tested on photoresist AZ5214E coated silicon substrate, with features as small as 160 nm beign obtained, replicating the original stencil with excellent agreement. The nanostencil was created by focused ion beam (FIB) milling, although other techniques such as femtosecond laser ablation or pattern transfer to fiber tip can also be employed. Stencils can be arbitrary or based on optical elementary designs such as line patterns, photonic crystals, Fresnel zone plates or photon sieve. Exact transfer of the inscribed pattern is obtained while in contact lithography, while proximity exposure enables complex modulation of the optical near-field by the phase and/or amplitude stencil mask. This allows for optical interference to occur, in full 3D space, rendering sub-wavelength spot focusing, annular pattern formation, as well as the formation of 3D complex shapes. Experimentally, a 405 nm laser beam with 17 mW power was launched into the core of UV-Visible single mode fiber (S405-XP) on which end a photon sieve was previously inscribed by FIB. This tip was scanned over the photoresist. Patterning consisted of 1Dscans, for which a minimum line width of 350 nm was obtained.Additionally, step-and-repeat patterning of the photon sieve fiber tip stencil was performed with, all features down to 160 nm being clearly resolved.

Plasmonic nanocavities can control light flows and enhance light-mater interactions at subwavelength scale, and thus can potentially be used as nanoscale components in integrated optics systems either for passive optical coupling, or for active optical modulation and emission. In this work, we investigated a new type of multilayered metal-insulator optical nanocavities that can support multiple localized plasmon resonances with ultra-small mode volumes. The total number of resonance peaks and their resonance wavelengths can be freely and accurately controlled by simple geometric design rules. Multi-resonance plasmonic nanocavities can serve as a nanoscale wavelength-multiplexed optical components in integrated optics systems, such as optical couplers, light emitters, nanolasers, optical sensors, and optical modulators.

New ways of employing optics at the micro and nanometer scale are of interest. This study analyses the most common two micro-mirror shapes (i.e., spherical and parabolic) that can be used for on-chip communication - in conjunction with fiber optics/waveguides. The classical conic sections that can be used for micro-mirrors are described and a technological approach to design and manufacture such devices is presented. Finally an optimization of the parabolic micro-mirror is achieved. Other micro-mirror shapes (e.g., elliptical and hyperbolic) can be approached and compared using the same procedure. The large area of applications of such micro-mirrors includes intra- or inter-chips communications, as well as free-space optics used for various optical systems: micro-optics, optical amplifiers, lasers, and wavelength converters.

We present high spatial-resolution label-free imaging with an electron-beam excitation-assisted optical microscope (EXA microscope). The EXA microscope improves the spatial resolution down to 100 nm. To realize the high spatial resolution, a nanoscale optical spot is generated by irradiating a fluorescent thin film with a focused electron beam whose spot size is less than 10 nm. The size of the optical spot becomes smaller than the diffraction limited spot size and is reduced to about 100 nm, because the light emission is localized in nanometer-sized region. In this microscopy, it is not necessary to label a specimen for imaging beyond the diffraction limit of the light. The specimen stage is separated from the vacuum chamber of the scanning electron microscope by the fluorescent thin film and a specimen under atmospheric pressure can be imaged. We demonstrated that the high spatial resolution absorption contrast imaging of the crystal of vitamin B9 having absorption at UV wavelengths. The absorption wavelength matches with the wavelength of the emission of the fluorescent thin film we deposited. The fine crystal structure was imaged beyond the optical diffraction limit. The image contrast corresponded with the thickness of the crystal measured with an atomic force microscope (AFM). The illumination light is absorbed with the vitamin B9 crystal and the intensity of the transmitted light depends on the thickness of the vitamin B9 crystal. The EXA microscope is useful for analysis of growth of a crystal, bio-imaging, and so on.

Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. While hyperbolic responses are normally achieved with metamaterials, hexagonal boron nitride (hBN) naturally possesses this property due to the anisotropic phonons in the mid-infrared. Using scattering-type scanning near-field optical microscopy, we studied polaritonic phenomena in hBN. We performed infrared nano-imaging of highly confined and low-loss hyperbolic phonon polaritons in hBN. The polariton wavelength was shown to be governed by the hBN thickness according to a linear law persisting down to few atomic layers [1]. Additionally, we carried out the modification of hyperbolic response in meta-structures comprised of a mononlayer graphene deposited on hBN [2]. Electrostatic gating of the top graphene layer allows for the modification of wavelength and intensity of hyperbolic phonon polaritons in bulk hBN. The physics of the modification originates from the plasmon-phonon coupling in the hyperbolic medium. Furthermore, we demonstrated the “hyperlens” for subdiffractional focusing and imaging using a slab of hBN [3]. References [1] S. Dai et al., Science, 343, 1125 (2014). [2] S. Dai et al., Nature Nanotechnology, 10, 682 (2015). [3] S. Dai et al., Nature Communications, 6, 6963 (2015).

Enantiomer separation is a critical step in many chemical syntheses, particularly for pharmaceuticals, but prevailing chemical methods remain inefficient. Here, we introduce an optical technique to sort chiral specimens using coaxial plasmonic apertures. These apertures are composed of a deeply subwavelength dielectric channel embedded in silver (or gold) and can stably trap sub-20-nm dielectric specimens. Using both full-field simulations and analytic calculations, we first show that selective trapping of enantiomers can be achieved with circularly polarized illumination and proper index-matching of the immersed liquid with the particles being trapped. Opposite enantiomers experience distinct trapping forces in both sign and magnitude: one is trapped in a deep potential well while the other is repelled with a potential barrier. These potentials maintain opposite signs across a range of chiral polarizabilities and enantiomer-aperture separations. We also demonstrate how atomic force microscopy can be used to directly probe the near field optical forces from our coaxial nano-aperture. Our measurement reveals the spatial distribution of the optical near-field forces on a nanometer-sized dielectric specimen. To directly visualize the enantio-selective optical forces, we pattern silicon AFM-probes with chiral patterns. Our near-field force mapping indicates a differentiable force in the piconewton range on the chiral probes, exerted by our coaxial aperture with circularly polarized illumination. Our theoretical and experimental demonstrations indicate that the interaction of chiral light and chiral specimens can be mediated by achiral plasmonic apertures, providing a possible route toward all-optical enantiopure syntheses.

The fourth generation optics (4G optics) enables the realization of novel optical components (lenses, gratings, vector vortices, etc.) by patterning the optical axis orientation in the plane of an anisotropic film. Such components exhibit near 100% diffraction efficiency for wavelengths meeting half-wave retardation condition. In this framework, we have advanced a step-forward by realizing different diffractive waveplates (DWs) with arbitrary spatial patterns of the optical axis orientation by exploiting the capability of a Digital Spatial Light Polarization Converter (DSLPC). The DSLPC is based on a reflective, high resolution Spatial Light Modulator (SLM) combined with an “ad hoc” optical setup. The most attractive feature of the use of a DSLPC for photoalignment is that the orientation of the alignment layer, and therefore of the fabricated liquid crystal (LC) or liquid crystal polymer (LCP) DWs, can be specified on a pixel-by-pixel basis. By varying the optical magnification or de-magnification between the SLM and the alignment layer, the spatial resolution of the photoaligned layer can be adjusted to be optimal for each application. We show that with a simple “click” it is possible to record different high resolution optical components as well as arbitrary patterns ranging from lenses to invisible and even dual labels.

The ability to stimulate, track, and record biological processes with as many data channels as possible is central to decoding complex phenomena in the body. For example, many biological processes involve small mechanical cues that can help drive chemical reactions and/or initiate responses to external stimuli. However, to measure these nanomechanical events, specialized tools are required that can not only achieve piconewton force resolution, but be able to record from multiple sites while maintaining a small footprint to allow embedded or intracellular measurements. This is challenging for state-of-the-art instruments such as atomic force microscopes or optical traps due to the difficulty in multiplexing, their size, and feedback mechanisms. Here we describe a new nanofiber-optic platform that can detect sub-piconewton forces by monitoring far-field scattering signals of plasmonic nanoparticles moving within the near-field. To provide mechanical resistance to the nanoparticles, and allow quantitative forces to be extracted, compressible polymer claddings have been designed that have tunable spring constants and chemical compositions. The transduction mechanism is demonstrated both on detecting local contact forces acting on the nanoparticles as well as acoustic waves propagating in the medium. Because of the small cross-sectional areas ( 1 mm), these nanofibers can also be inserted deep into tissue to locally excite and collect signals from single cells (e.g., neurons) with minimal invasiveness. Experiments focused on stimulating and recording from brain tissue will be discussed.

The improvement of the optical devices in this decade, such as the MEMS-SLM ( Micro Electro Mechanical Systems- Spatial Light Modulator ) and wave front sensor with micro lens device, is making adaptive optics commonly available. It also gives the new basis of the design of adaptive optics with the improved accuracy and the compactness. We have developed an adaptive optics bench from such a point of view, and the application to the optical microscope has attained effective results in the observation of the live cell samples. In this presentation, our recent results will be shown. The result includes analysis of blur by the fine structures in biological sample and result of the image correction by the adaptive optics.

Photonic microcavities (PMC) coupled through their evanescent field are used for a large variety of classical and quantum devices. In such systems, a molecular-like spatial delocalization of the coupled modes is achieved by an evanescent tunnelling. The tunnelling rate depends on the height and depth of the photonic barrier between two adjacent resonators and therefore it is sensitive to the fabrication-induced disorder present in the center of the molecule. In this contribution, we address the problem of developing a post fabrication control of the tunnelling rate in photonic crystal coupled PMCs. The value of the photonic coupling (proportional to the tunnelling rate) is directly measured by the molecular mode splitting at the anticrossing point. By exploiting a combination of tuning techniques such as local infiltration of water, micro-evaporation, and laser induced non thermal micro-oxidation, we are able to either increase or decrease the detuning and the photonic coupling, independently. Near field imaging is also used for mapping the modes and establish delocalization. By water micro-infiltration, we were able to increase the photon coupling by 28%. On the contrary, by laser induced non thermal oxidation, we got a reduction of g by 30%. The combination of the two methods would therefore give a complete control of g with excellent accuracy. This could make possible the realization of array of photonic cavities with on demand tunnelling rate between each pair of coupled resonators. We believe that this peculiar engineering of photonic crystal molecules would open the road to possible progress in the exploitation of coherent interference between coupled optical resonators both for quantum information processing and optical communication.

International audience; Hybrid structures are needed to fully exploit the great advantages of Si photonics and several approaches have been addressed where Si devices are bonded to different materials and nanostructures. Here we study the use of semiconductor carbon nanotubes for emission in the 1300 nm wavelength range to functionalize Si photonic structures in view of optoelectronic applications. The Si micro-rings are fully characterized by near field forward resonant scattering with 100 nm resolution. We show that both TE and TM modes can be addressed on the top of the micro-rings in a vectorial imaging of the in-plane polarization components. We coupled the Si micro-resonators with selected carbon nanotubes for high photoluminescence emission. Coupling nanotubes with the evanescent tails in air of the electric field localized in the photonic modes of the micro-resonators is demonstrated by sharp resonances over imposed to the nanotube emission bands. By mapping the Si and the nanotube emission we demonstrate that strong enhancement of the nanotube photoluminescence can be achieved both in the photonic modes of micro-disks and slot micro-rings, whenever the spatial overlap between nano-emitters and photonic modes is fulfilled.

Optical near-field technologies such as solid immersion lenses and hyperlenses are candidate solutions for high resolution and high throughput wafer inspection and metrology for the next technology nodes. Besides sub-diffraction limited optical performance, these concepts share the necessity of extreme proximity to the sample at distances that are measured in tens of nanometers. For the instrument this poses two major challenges: 1) how to measure the distance to the sample? and 2) how to position accurately and at high speed? For the first challenge near-field thermal radiation is proposed as a mechanism for an integrated distance sensor (patent pending). This sensor is realized by making a sensitive calorimeter (accuracy of 2:31nW root sum squared). When used for distance measurement an equivalent uncertainty of 1nm can be achieved for distances smaller than 100 nm. By scanning the distance sensor over the sample, thermal profilometry is realized, which can be used to inspect surfaces in a non-intrusive and non-contact way. This reduces wear of the probe and minimizes the likelihood of damaging the sample.

Orbital angular momentum (OAM) states of light have been recently considered in new mode-division multiplexing techniques in order to increase the bandwidth of today's optical networks. Many optical architectures have been presented and exploited in order to sort the different OAM channels. Here we present a diffractive version of the sorting technique based on log-pol optical transformation and we further improve the miniaturization level by integrating the two components into a single diffractive optical element. Samples have been fabricated with high-resolution electronbeam lithography and characterized in the optical range. The presented design is promising for integration into nextgeneration optical platforms performing optical processing of OAM modes, for applications both in free-space and optical fibers.

Tip Enhanced Raman Scattering (TERS), a technique that provides molecular information on the nanometer scale, has been a subject of great scientific interest for 15 years. But regardless of the recent achievements and applications of TERS, ranging from material science and nanotechnology, strain measurement in semiconductors, to cell biological applications, the TERS technique has been hampered by extremely long acquisition times, measured in hours, required for collection of reasonably high pixel density TERS maps. In this talk, specifics of the TERS setup that enable fast, high pixel density nano-Raman imaging will be discussed: The innovative integration of technologies brings high-throughput optics and high-resolution scanning for high-speed imaging without interferences between the techniques. The latest developments in near-field optical probes also provide reliable solutions for academic and industrial researchers alike to easily get started with nanoscale Raman spectroscopy. Thanks to those latest instrumental developments, we will present the nanoscale imaging of chemical and physical properties of graphene, carbone nanotubes and self-assembled monolayers of organic molecules, with a spatial resolution routinely obtained in TERS maps in the 15 - 20 nm range and a best resolution achieved being of 7 nm

A conical tip made out of good conductive metal can be used to efficiently localize the optical field at the apex of the tip. For a tip of finite length both a field singularity (lightning rod effect) and a surface plasmon resonance contribute to the E-field enhancement. A strongly absorbing superconducting nanodetector placed in the optical near-field of the tip shows enhanced optical absorption. The design of an optimal tip- detector system is non-trivial because the strong damping by the detector shifts the resonance wavelength of the tip and significantly lowers the quality factor of the resonance. We compare calculations of the field enhancement of a bare tip to the absorption enhancement in the detector in the presence of the tip as a function of tip length, apex radius and semi-angle of the cone. The resonance of a 225 nm long gold tip in the presence of a detector occurs at 1000 nm and is red-shifted by 150 nm compared to the resonance of a bare tip.

Focused ion beam (FIB) patterning of 3D topography on optical fiber tips for application in stand-alone, rugged and simplified setups for optical tweezers cell sorters, optical near-field lithography and optical beam profile engineering are reported. We demonstrate various configurations based on single-step FIB patterning, multiple-step FIB processing and hybrid approaches based on optical fiber pre- and post-FIB treatment with either etching, fusion splicing, photopolymerization or electroplating steps for optical fiber texture, topography and composition engineering. Different conductive coatings for minimal charge accumulation and beam drift are studied with the relative merits compared. Furthermore optimal beam parameters for accurate pattern replication and positioning are also presented. Measured experimental field profiles are compared with numerical simulations of fabricated optical fiber tips for fabrication accuracy evaluation. Applications employing these engineered fiber tips in the field of optical tweezers, optical vortex generation, photolithography, photo-polymerization and beam forming are presented.

In order to overcome the problem of low spatial resolution in ordinary optical microscopy, microscopic indirect imaging with super resolution is introduced. This article elaborates three aspects of the status and trends of indirect imaging system: first, the theories in variable optical coupling transmission and the super resolution metrology; second, metrology method and model of multidimensional optical wave vector parameter; third, the theory in super resolution indirect vectorial parameter imaging by modulation and compensative imaging of multi-spatial dimensions and physical parameters.

Diffractive optical elements offer a high degree of freedom for controlling phase and spectral behavior in optical designs. This enables new and compact optical sensors and measurement systems. We show several recent applications which bene t from unique properties of diffractive optical elements. The applications include: field aberration correction e.g. for microscopic projection applications through microscope objective lenses, a 200 channel microscope objective integrated optical addressing system, diffractive/refractive hybrid optics for high efficiency beam shaping and deflection angle enlargement of spatial light modulators.

Near field optics concepts have introduced a paradigm shift in a wide variety of engineering fields in the recent past and the most significant applications of this fundamental physics concepts have been in the applied engineering problems such as improved broad band light absorption thereby enhancing the conversion efficiency of thin silicon solar cells. Also, for writing patterned structures or features using non contact optical methodologies have enabled near field optics assisted fabrication and related applications. The technology involving optics concepts and methodologies targeting energy sector have seen the impact of the same with a challenging trend to achieve smaller features or devices with micro- or nano-scale features. This demands automatically the need for achieving much smaller features beyond the forecasted sub- 30nm feature patterning methodologies. To meet such demands, a new branch of near- field optical concepts for improving patterning resolution has started developing which have been receiving considerable attention for its ability to produce high density sub-wavelength features that can find tremendous energy harvesting applications. This paper in this context mainly focuses on the review of different near field optical concepts and approaches developed for patterning by the author’s group at NTU. Different concepts were explored incorporating surface Plasmon waves ( LSPs, SPPs, LRSPs), gap modes as well as their interference in order to high resolution features and pattern dimensions at nano-scales. The absorbance of near band gap light is small and hence structuring of thin film solar cell is very important for increasing the absorbance by light trapping. The manuscript conclude by correlating the above said aspects and the challenges in achieving improved light conversion in thin film solar cells. Published version

International audience; Incorporating resonant optical properties of metal nanostructures into nanoscale applications such as ultrahigh density storage devices, nanoelectronics, and nanophotonics has gained considerable interest within the last years. Recent advances in hybrid and molecular plasmonics are presented. The approach relies on near-field energy transfer between metal nanoparticles and other molecular material, and is not diffraction-limited. We will see that optical nanosources supported by metal nanoparticles can be used for controlling/triggering photochemical and photo physical processes involving photons, charges and motion transfers at the nanoscale. In particular, three examples will be presented and commented: free radical photopolymerization, photo isomerization and nanoscale strong coupling. These examples open new routes including optical near-field photography of ultra confined fields, mode hybridizing in single nanoparticles, molecular optical nanomotors, and new anisotropic nanoemitters.

Optical microscopy technology has ac hieved great improvements in the 20th century. The detection limit has reached about twenty nanometers (with near-field optics, STED, PALM and STORM). But in the application areas such as life science, medical science, clinical treatment and especially in vivo dynamic measurement, mutual restrictions still exist between numeric aperture/magnification and working distance, fluorescent dependent, and between resolution and frame rate/field size, etc. This paper explores a hyperspectral scanning super-resolution label free molecules imaging method based on the white light interferometry. The vertical detection resolution was approximate to 1 nm which is the thickness of a single molecular layer and dynamic measuring range of thickness reaches to 10 µm. The spectrum-shifting algorithm is developed for robust restructure of imag es when the pixels are overlapped. Micr o-biochip with prot ein binding and DNA amplification could be detected by using this spectral scanning super-resolution molecules imaging in label free. This method has several advantages as following: Firstly, the decoding and detecting steps are combined into one step. It makes tests faster and easier. Secondly, we used thickness-coded, minimized chips instead of a large microarray chip to carry the probes. This accelerates the interaction of the biomolecules. Thirdly, since only one kind of probes are attached to our thickness-coded, minimized chip, users can only pick out the probes they are interested in for a test without wasting unnecessary probes and chips. Keywords: Interferometric detection, label-free, molecular diagnostics, biochip encoding

Nanopore-based sensing is an attractive candidate for developing single-molecule DNA sequencing technology. Recently, optical detection with a parallel nanopore array has been demonstrated. Although this method is a promising approach to develop high thorough-put measurement, the approach requires observation at low-background condition. In this paper, we propose a new optical method for nanopore DNA sequencing with high resolution and a high signal-tonoise ratio. We use ultraviolet light for the excitation of a fluorescent probe and a nanopore in a silicon membrane. Because silicon has a large refractive index and an extinction coefficient at ultraviolet wavelengths, light transmission thorough the membrane is negligible. This contributes to low background measurement of fluorescence from fluorophore-labeled DNA strands. In addition, the z-polarization component of the electric field is attributed to generating a large electric field gradient at the nanopore exit due to its boundary condition at the silicon surface. Our numerical electromagnetic simulation revealed that the z-component electric field was dominant compared to the xcomponent electric filed. The intensity of the electric field increased steeply in 2 nm, when ultraviolet light of 375nm wavelength was focused on a 10nm-thick silicon membrane with a 7 nm-diameter nanopore. This steeply increasing electric field can be sufficient resolution for the sequencing of designed DNA polymer. Finally, our experimental results demonstrated optical detection of single DNA translocation events with a high signal-to-noise ratio under applied voltage.

As an amorphous material with full inversion symmetry, silica-based microstructures cannot possess significant secondorder nonlinearity. We recently developed a method that can potentially overcome this deficiency by coating a silica fiber taper with layers of radially aligned nonlinear molecules. The coating process can be accomplished through layerby- layer self-assembly, where the alignment of the nonlinear molecules is maintained through electrostatic interaction. As a result, the nonlinear fiber structures are thermodynamically stable and can generate significant second-order nonlinear responses despite their full rotational symmetry. This prediction has been experimentally confirmed through SHG measurements. To further enhance the overall second-order nonlinearity, we have developed an UV-ablation-based approach that can generate second-order nonlinearity that is spatially periodic along the fiber taper. Our preliminary experiments suggest that SHG intensity can be enhanced by such quasi-phase-matching configurations. We can also use the self-assembly approach to construct tunable plasmonic systems. As a proof-of-concept study, we assembled swellable polymer films over a planar Au substrate through layer-by-layer assembly and covered the swellable polymer with a monolayer of quantum dots. After immersing the swellable plasmonic structure in solution and adjusting its pH value, we used a fluorescence lifetime based approach to demonstrate that the thickness of the swellable polymers can be modified by almost 400%. The fluorescence lifetime measurements also confirmed that the plasmonic resonance can be significantly modified by the swellable polymers.

The focusing efficiency of binary Fresnel zone plate lenses is fundamentally limited and higher efficiency requires a multi step lens profile. To overcome the manufacturing problems of high resolution and high efficiency multistep zone plates, we investigate the concept of stacking two different binary zone plates in each other’s optical near-field. We use a coarse zone plate with π phase shift and a double density fine zone plate with π/2 phase shift to produce an effective 4- step profile. Using a compact experimental setup with piezo actuators for alignment, we demonstrated 47.1% focusing efficiency at 6.5 keV using a pair of 500 μm diameter and 200 nm smallest zone width. Furthermore, we present a spatially resolved characterization method using multiple diffraction orders to identify manufacturing errors, alignment errors and pattern distortions and their effect on diffraction efficiency.

In this paper we report on the progress in building the superresolution microscope using optical vortices. The outline of the general idea is presented. Some of the specific problems are discussed in more details. Specifically, the scanning method by vortex lens movement is discussed.

Interest in plasmonic lenses dates back to the seminal paper of Pendry [Phys. Rev. Lett. 85, 3966 (2000)] who has shown that superresolution is possible due to imaging through a negative-refractive-index material. Experimental verifications of near-field to near-field imaging properties of a single Ag nanolayer have proven that a resolution reaching one-sixth of the illumination wavelength is possible. The images have been recorded in a photoresist spin-coated onto an Ag layer. In this paper, images are recorded using a scanning near-field optical microscope (SNOM) working in the transmission mode with tapered-fibre metal-coated probes and aperture diameters

Attosecond physics, centering on the control of electronic matter waves within a single cycle of the optical laser’s driving field, has led to tremendously successful experiments with atoms and molecules in the gas phase. We show that pivotal phenomena such as elastic electron rescattering at the parent matter, a strong carrier-evenlope phase sensitivity and electronic matter wave intereference also show up in few-cycle laser driven electron emission from nanometric sharp metal tips. Furthermore, we utilize spectral signatures to measure the enhanced near-field with a spatial resolution of 1nm.

Microstructured Optics enable a new class of optics - new in terms of enabling functionality that has not been achieved so far, as well as in terms of reducing size while increasing performance of existing solutions significantly. In modern optics several demands exist for implementing microstructured optical components. For example, diffractive optical elements (DOEs) are of considerable advantage in combination with refractive lenses to form so-called hybrid optical systems. The inverse chromatic dispersion of diffraction in contrast to refraction opens new possibilities for the compensation of chromatic aberrations. Furthermore, the realization of a diffraction grating on a concave optical surface allows the functional integration of imaging and dispersing in one single optical component, which is a key enabler for miniaturization of spectroscopic systems. In the sophisticated illumination systems microstructured beam shaping elements play an essential role. Micro- and nanostructures in the subwavelength range open alternative solutions for antireflective properties and polarization management.

The Paper describes the designing of the multi-spectral sensor optical system using off-axis three-mirror reflective optics which is particularly suitable for wide-field, wide spectral range, multi-spectral and high resolution sensor imaging optics. The off-axis three-mirror reflective optics provides an obstruction free field of view and high spatial resolution over the wide-field, the relay optics is used to adjust the multiplication factors for infrareds. The optical system concludes three-mirror optics with large relative aperture and infrared relay optics, the dichroic mirror and filters subdivide the wide spectral range into nine bands, each corresponds to respective field. The working wavelength ranges from visible to medium wave band. The paper also analyses the selection of dichroic schemes. The MTF of each branch at respective fields which are all near the diffractive limit are also given. The MTF of the camera is also forecasted at the end of the paper.

We studied the near-field optical properties of colloidal gold nanocubes (GNCs) using a photochemical imaging method. This method is based on the vectorial molecular displacements, of photosensitive azo-dyes, which are sensitive to the polarization of the optical near-field of the GNCs. We analyzed the spatial confinement of both electromagnetic hot and "cold" spots with a spatial resolution up to 15nm (λ/35). The new concept of cold spot presents valuable and complementary electromagnetic information to the well known electromagnetic hot spot. We demonstrated that cold spots are highly sensitive to polarization and can be much more confined than hot spots enabling them to be applied in high resolution imaging and spectroscopy.

In plasmonic nano lithography, a photoresist responds to the localized electric field which decays evanescently in the direction of depth. A simple analytic model is suggested to predict profiles of exposed and finally developed pattern with a finite contrast of photoresist. In this model, the developing process is revisited by accounting the variation of dissolution rate with respect to expose dose distribution. We introduce the concept of nominal developing thickness (NDT) to determine the optimized developing process fitting to the isointensity profile. Based on this model, we obtained three dimensional distribution of near-field of bowtie shaped plasmonic nano aperture in a metal film from the near-field lithography pattern profile. For the near-field exposure, we fabricated a nano aperture in a aluminum metal film which is coated on the contact probe tip. By illuminating 405 nm diode laser source, the positive type photoresist is exposed by the localized electric field produced by nano aperture. The exposed photoresist is developed by the TMAH based solution with a optimum NDT, which leads the developing march encounters the isoexposure contour at threshold dose. From the measurement of developed pattern profile with a atomic force microscope (AFM), the three-dimensional isoexposure (or iso-intensity) surface at the very near region from the exit plane of an aperture (depth: 5 ~ 50 nm) is profiled. Using the threshold dose of photoresist and exposure time, the absolute intensity level is also measured. The experimental results are quantitatively compared with the calculation of FDTD (finite- difference time-domain) method. Concerning with the error in exposure time and threshold dose value, the error in measurement of profile and intensity are less than 6% and 1%, respectively. We expect the lithography model described in this presentation allows more elaborated expectation of developed pattern profile. Furthermore, a methodology of mapping is useful for the quantitative analysis of near-field distribution of nano-scale optical devices.

A computational study of the far field transmittance of subwavelength palladium (Pd) structures is presented with a view of improving optical detection of hydrogen (H2) with subwavelength structures. In previous reports, the optical responses of the far field transmittance spectra with subwavelength hole arrays were used to detect Pd hydride which are formed upon hydrogen exposure. Upon hydride formation, the wavelength of the main transmittance peak of the subwavelength Pd hole arrays showed a shift to longer wavelengths. In this report, the simulated optical response of transmittance spectra upon H2 exposure with the subwavelength Pd hole array and rod array were compared. Our computational studies show that the dip wavelength of rod arrays have larger shifts than that of the peak wavelength of hole arrays upon H2 exposure. The reason of the large optical response of the rod arrays lies in the effect of the expansion of the Pd layer upon H2 exposure that results in larger shift to longer wavelengths for the rod arrays. The rod arrays offer potential advantages to increase the optical response to H2 exposure of Pd subwavelength structures.

We present a rigorous electromagnetic theo ry of the electromagnetic power emitted by a dipole located in the vicinity of a multilayer stack. We applied this formalism to a luminescent molecule attached to a CMOS photodiode surface and report light collection efficiency larger than 80% toward the CMOS silicon substrate. We applied this result to the development of a low-cost, simple, portable device based on CMOS photodiodes technology for the detection and quantification of biological targets through light detection, presenting high sensitivity, multiplex ability, and fast data processing. The key feature of our approach is to perform the analytical test directly on the CMOS sensor surface, improving dramatically the optical detection of the molecule emitted light into the high refractive index semiconductor CMOS material. Based on adequate surface chemistry modifications, probe spotting and micro-fluidics, we performed proof-of-concept bio-assays directed against typical immuno-markers (TNF- D and IFN- ). We compared the developed CMOS chip with a commercial micro-plate reader and found similar intrinsic sensitivities in the pg/ml range.

In the past several years, surface plasmon polaritons (SPPs) excitation by vector beams or vortex beams has been greatly studied, and many significant achievements have been obtained, which show wide applications in near-field optics. In the paper, we study SPPs excited by radially polarized vortex beams, and concentrate on the influence of the phase distribution of vortex beams to SPP field distribution. Based on the vector diffraction theory, the expressions for SPP fields excited by radially polarized vortex beams are derived, and the orbital angular momentum (OAM) is calculated. We numerically simulate the intensity and phase distributions of SPP fields excited by radially polarized vortex beams with different topological charges, and analyze the corresponding orbital angular momentum (OAM). The results show that by changing the topological charge, we can flexibly modulate the intensity and phase distribution, and control the OAM, which presents us with more useful applications in special fields, such as optical trapping, near-field optical devices, particles rotation, and so forth.

Contemporary optical effects and photonic component necessary for the realization of nanoscale integrated photonic circuit for developing lab-on-a-chipincluding light sources, de tectors and filters is summarized. We present the concept of a lab-on-a-chip for the next generation optoelectronics and biophotonic industry including novel nanoscale material systems for lasers and detectors. Using principles such as plasmonics and near-field optics highly efficient nano-photonic lasers or modulators can be realized. The light source can be tuned from the UV to the visible range using ion implantation of noble metal such as Ag or Au in Silicon or silica. The presence of Ag or Ag nanoparticles can result in a significant enhancement of the light emission in the UV, green or red wavelength regime. Novel molecular electronics materials has been used to design olegonucleotide based photodetectors on transparent substrates for the detection of analytes in an all-optical system. Either a transparent GaN semiconductor or glass can be used as an substrate. Hybrid photonic crystal based microfluidic channels synthesized using hydrogel material can be optimized to control the flow of fluid using light. In this paper, the de vice components developed at the Univers ity of North Texas will be presented for the realization of a lab-on-a-chip. Keywords: Nanophotonics, plasmonic light emitters, nonlinear optical sources, tunable photonic crystals, molecular wires, lab-on-a-chip

The optical near-field of lithography-defined gold nanostructures, arranged into regular arrays on a gold film, is characterized via ablation of a polymer coating by laser illumination. The method utilizes femto-second laser pulses from a laser scanning microscope which induces electrical field enhancements on and around the gold nanostructures. At the positions of the enhancements, the ablation threshold of the polymer coating is significantly lowered creating subdiffractional topographic modifications on the surface which are quantified via scanning electron microscopy and atomic force microscopy. The obtained experimental results for different polymer coating thicknesses and nanostructure geometries are in good agreement with theoretical calculations of the near field distribution for corresponding enhancement mechanisms. The developed method and its tunable experimental parameters show that the different stages in the ablation process can be controlled and characterized making the technique suitable for characterizing optical near-fields of metal nanostructures.

We review our work on nanopatterning in azo-polymer films by single, two- and multi-phopton driven molecular motion in solid bulk polymer. It is now known that light induced molecular movement occurs below the polymer glass transition temperature by chromophores photoisomerization via either linear or nonlinear absorption, and in this paper we will show that nanoscale polymer movement is induced by a tightly focused laser beam in an azo-polymer film just at the diffraction limit of light. The deformation pattern which is produced by photoisomerization of the azo dye is strongly dependent on the incident laser polarization and the longitudinal focus position of the laser beam along the optical axis. The anisotropic nanofluidity of the polymer film and the optical gradient force played important roles in the light induced polymer movement. We explored the limits of the size of the photo-induced deformation, and we found that the deformation depends on the laser intensity and the exposure time. The smallest deformation size achieved was 200 nm in full width of half maximum; a value which is nearly equal to the size of the diffraction limited laser spot. Furthermore, a nano protrusion was optically induced on the surface of the films, beyond the limit of light diffraction, by metal tip enhanced near-filed illumination. A silver coated tip was located inside the diffraction limited spot of a focused laser beam (460 nm), and an enhanced near-field, with 30 nm light spot, was generated in the vicinity of the tip due to localized surface plasmons. The incident light intensity was carefully regulated to induce surface nanodeformation by such a near-field spot. A nano protrusion with 47 nm full width of half maximum and 7 nm height was induced. The protrusion occurs because the film is attracted towards the tip end during irradiation. At the top of the protrusion, an anisotropic nanomovement of the polymer occurs in a direction nearly parallel to the polarization of the incident light, and suggests the existence at the tip end of not only a longitudinal, i.e., along the tip long axis, but also a lateral component of the electric field of light. The azo-polymer film helps map the electric field in the close vicinity of the tip. We also report on two-photon patterning of the films. Exposure of azo polymer films, which absorb in the visible range (λmax = 480 nm), to intense 920 nm irradiation leads to polarization dependent patterning which are associated with polymer nanomovement caused by photoselective two-photon cis ↔ trans isomerization, while irradiation at 780 nm induces multi-photon bleaching of the azo chromophore. These wavelengths hit bleaching and isomerization pathways in the chromophore, respectively.

Scattering of light is considered a nuisance in microscopy. It limits the penetration depth and strongly deteriorates the achievable resolution. However, by gaining active spatial control over the optical wave front it is possible to manipulate the propagation of scattered light far in the multiple scattering regime. These wave front shaping techniques have given rise to new high-resolution microscopy methods based on strong light scattering. This is based on the realization that scattering by stationary particles performs a linear transformation on the incident light modes. By inverting this linear transformation, one can focus light through an opaque material and even inside it. An extremely high resolution focus can be obtained using scatterers embedded in a high-index medium, where the diffraction limit for focusing is reduced by a factor n. We have constructed a scattering lens made of the high-index material gallium phosphide (GaP) which is transparent over most of the visible spectrum and has the highest index of all nonabsorbing materials in the visible range. This yields a focal spot resolution of less than 100 nm, and it seems theoretically possible to create a focus of order 70 nm. The system resolution of a microscope based on this lens could be substantially higher.n

A coating technique is being developed to correct the surface figure deviations in reflective-grazing-incidence X-ray optics. These optics are typically designed to have precise conic profiles, and any deviation in this profile, as a result of fabrication, results in a degradation of the imaging performance. To correct the mirror profiles, physical vapor deposition has been utilized to selectively deposit a filler material inside the mirror shell. The technique, termed differential deposition, has been implemented as a proof of concept on miniature X-ray optics developed at MSFC for medical-imaging applications. The technique is now being transferred to larger grazing-incidence optics suitable for astronomy and progress to date is reported.

In the aim to understand the nature of the propagation of an electromagnetic field in the near region, we study the interactions between an evanescent field and two different samples of spherical dielectric nanoparticles, i.e. a set of five particles and a single one. Each sample was studied in separated experiments. This is made by using a Photon Scanning Tunneling Microscope (PSTM) in the constant distance mode. We also analyze the obtained images and determine that the optical images show mainly interference between the evanescent field and the reflected field on the surface of the nanoparticles. Finally, we found that the perturbation of the evanescent field, produced by imperfections on the substrate, is negligible in comparison with the interactions intensity.