This PDF file contains the front matter associated with SPIE Proceedings Volume 10672, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Plasmon polaritons have revolutionized our world of nanophotonics. They have created a platform for enhanced light-matter interactions, propagation of light beyond the diffraction limit, and nanofocusing of electromagnetic energy. However, for applications in data processing and telecommunication, dissipation of optical energy in metallic waveguides is much beyond what can be tolerated for nanocircuitry. Recently other groups of polaritonic waves, namely photon polaritons, exciton polaritons, and Dirac plasmons have been demonstrated as possible candidates for nanophotonics1. Interestingly, a topological insulator like Bi2Se32, as well as heterostructures like graphene/hBN 3, can support coexisting polaritonic waves of all the kinds stated above. At THz frequencies and near to the Fermi energy level, those materials support both hyperbolic phonon polaritons and Dirac plasmons, whereas at infrared and visible ranges4,5 exists another channel for exciton-polariton mode. Here, we mainly discuss the dispersion of the surface polaritons and their spatiotemporal behaviors, at all the energy ranges stated above. We however mainly focus on an aspect of topological insulators which is less discussed beforehand, i.e. topological magnetoelectric effect6. We study the criteria for existence of propagating optical modes which are transversely bound at the interface of two materials. In particular, quite general cases are considered, where the materials involved are assumed to be anisotropic, but also demonstrating magneto-electric effects7. We also discuss the situations where the coexistence of Dirac and hyperbolic polaritons result in level repulsion. We further study the effect of topological magnetoelectric effect on the appearance of hybrid optical modes with various polarization states. In addition to surface polaritons, existence of wedges support another channel for long range propagation of hyperbolic polaritons, due to the coupling of two edge polaritons. We study here the behavior of hyperbolic wedge polaritons at visible and ultraviolet energy ranges. We discuss the radiation damping and long range propagation of hyperbolic wedge and surface polaritons, both theoretically and experimentally using electron energy-loss spectroscopy and finite-difference time-domain method. References 1 Basov, D. N., Fogler, M. M. & de Abajo, F. J. G. Polaritons in van der Waals materials. Science 354, aag1992 (2016). 2 Wu, J.-S., Basov, D. N. & Fogler, M. M. Topological insulators are tunable waveguides for hyperbolic polaritons. Phys. Rev. B 92, 205430 (2015). 3 Woessner, A. et al. Highly confined low-loss plasmons in graphene-boron nitride heterostructures. Nat. Mater. 14, 421-425 (2015). 4 Esslinger, M. et al. Tetradymites as Natural Hyperbolic Materials for the Near-Infrared to Visible. Acs Photon. 1, 1285-1289 (2014). 5 Talebi, N. et al. Wedge Dyakonov Waves and Dyakonov Plasmons in Topological Insulator Bi2Se3 Probed by Electron Beams. Acs Nano 10, 6988-6994 (2016). 6 Dziom, V. et al. Observation of the universal magnetoelectric effect in a 3D topological insulator. Nat. Commun. 8 15197 (2017). 7 Talebi, N. Optical modes in slab waveguides with magnetoelectric effect. J. Opt.-Uk 18, 055607 (2016)

Metal nanoparticles demonstrate unique optical properties that are mostly due to localized surface plasmon resonances (LSPRs). In addition, when nanoparticles are arranged in arrays (metasurfaces), their responses can be modified by the presence of the neighboring particles. As a result, sharp spectral features can be observed. Such features, called surface lattice resonances (SLRs), are related to the appearance of diffraction orders in the optical response. Both types of resonances can lead to local-field enhancement and thereby boost nonlinear optical effects. For the particular case of second-harmonic generation (SHG) the sample needs to be also non-centrosymmetric. This condition is fulfilled when, for example, V-shaped nanoparticles are used in the array. Increasing the number of particles typically increases the optical density, which should increase the nonlinear response with the square of the particle density. This approach, however, has its limitations because, when the particles are too close to each other, the quality of the LSPRs decreases leading to an effect opposite to the desired. Here, we will show the counterintuitive effect that the nonlinear response can be enhanced by reducing the number of particles in the array. In order to verify our idea, we use two arrays of V-shaped gold nanoparticles fabricated on a glass substrate by electron-beam lithography and lift-off methods. The particles are distributed in 500 x 500 nm2 square arrays in two configurations: i) all lattice points are filled with particles (V1) or ii) every other particle in the lattice is removed in a way that the remaining particles form a rotated (by 45°) square array with a pitch of 707 nm (V2). Both samples have two eigenpolarizations: one along the symmetry axis (y) of the V shape and other in the perpendicular direction (x). In the SHG experiments, the incident beam from an optical parametric oscillator was incident on the sample. Polarizers and a half-wave plate were used to control the polarization of the fundamental (1000 – 1300 nm) and second-harmonic beams. The SHG signal was collected by a photon counting system. The sample V2, that has reduced (by a factor of 2) density of particles in the array, shows the expected decrease in the strength of the resonance peak (1151 nm) and a slight redshift of the resonance wavelength with respect to the sample V1 (1081 nm). In order to achieve fair comparison of the nonlinear signals, we tuned the incident wavelength to the position of approximately equal losses for both samples (1135 nm). The sample V2 is found to have, by a factor of 7, stronger response than sample V1. Such enhancement in the nonlinearity is related to the improvement in the quality of the resonance for sample V2, for which the width of the resonance is reduced by ~30% compared to V1. This is due to SLRs that are present for sample V2. Our results are in good agreement with calculations by using an approach based on the discrete-dipole approximation.

A gap plasmon is an electromagnetic wave propagating in a gap between two noble metal surfaces. Such gap plasmons have previously been studied using only a classical description of the noble metals, but this model fails and shows unphysical behavior for sub-nanometer gaps. To overcome this problem quantum spill-out is included in this paper by applying Density-Functional Theory (DFT), such that the electron density is smooth across the interfaces between metal and air. The mode index of a gap plasmon propagating in the gap between the two metal surfaces is calculated from the smooth electron density, and in the limit of vanishing gap width the mode index is found to converge properly to the refractive index of bulk metal. When neglecting quantum spill out in this limit the mode index shows unphysical behavior and diverges instead. The mode index is applied to calculate the reflectance of an ultrasharp groove array in silver, as gaps of a few nm are found in the bottom of such grooves. At these positions the gap plasmon field is highly delocalized implying that it mostly exists in the bulk silver region where absorption takes place. Surprisingly, when the bottom width is a few nm and the effect of spill out at a first glance seems to be negligible, strong absorption is found to take place 1-2 Å from the groove walls as a consequence of the dielectric function being almost zero at these positions. Hence quantum spill out is found to significantly lower the reflectance of such groove arrays in silver.

Epsilon-near-zero materials are ideal platforms for nonlinear optics. Extreme electric field enhancements are predicted when a transverse-magnetic polarized field impinges obliquely on a film of material whose real part of the dielectric permittivity approaches zero. Under these circumstances, the component of the electric field with polarization normal to the film surface is enhanced by a factor proportional to the inverse square root of the dielectric permittivity. Nonlinear processes benefit from such uniquely favorable field localization, whether the condition is achieved in natural or artificial materials. Nonlinear optical processes have also been shown to be affected by the interference mechanism that occurs when two counter-propagating beams/pulses interact. Counter-propagating pulse dynamics has been investigated for surface plasmons and guided beams, they have been used for direct characterization of ultra-short pulses, to control emission of high-harmonics and to indirectly measure the phase mismatch of waveguides. Finally, they have been studied also in one dimensional photonic crystals and negative index materials. However, all these examples rely on either phase-matching or the availability of photonic resonances. Here we demonstrate that, thanks to the ability of epsilon-near-zero materials to efficiently support nonlinear processes in the absence of phase-matching or resonant conditions, one can control harmonic generation process by altering the phase of two non-collinear counter-propagating beams. We investigate the dynamics of two non-collinear counter-propagating beams impinging on an epsilon-near-zero slab and evaluate the modulation of the second and third harmonic signals as a function of the phase difference between the two sources. The calculations are performed considering a 100nm-thick slab of indium-tin-oxide (ITO). The results confirm that epsilon-near-zero media are exceptional platforms for nonlinear optics, providing a novel path to control these processes, including the possibility to easily characterize optical pulses.

Nanoparticles exhibit various optical properties arising from scattering and absorption due to polariton excitation. The resulting frequency and amplitude is dependent on several factors such as particle size, shape, and dielectric environment. By modifying the environment of the nanoparticle surface, in particular by encapsulating an individual nanoparticle within a membrane bilayer comprising defined phospholipids, these properties may be utilised to interrogate molecular interactions adjacent to the particle surface to useful levels of sensitivity. We describe the underlying rationale of these properties and characterise the preparation and behaviour of the nanoparticles. We indicate the potential this approach may have for sensing and screening in analytical biomolecular technology by demonstrating that it can be utilised to reveal the kinetics of the molecular interactions of membrane associated events. We also indicate that the technique may yield higherorder structural information of the macromolecule-membrane interactions in a highly sensitive manner and discuss the physical origins of these potentially more exotic phenomena.

The development of planar functional junction provides continuous, single-atom thick, in-plane integrated circuits. The production of atomic contacts of different materials (hetero/homostructures) is still a challenging task for 2D materials technology. In this paper we describe a new method of formation of a photosensitive junction by femtosecond laser pulses patterning of graphene FET. The laser-induced oxidation of graphene goes under high intensity laser pulses, which provide nonlinear effects in graphene like multiphoton absorption and hot carrier generation. The process of laser induced local oxidation is studied on single-layer graphene FET produced by wet transfer of CVD grown graphene on copper foil onto a Si/SiO₂ substrate. The 280 fs laser with 515 nm wavelength with various pulse energies is applied to modify of local electrical and optical properties of graphene. Thus, the developed process provides mask-less laser induced in-plane junction patterning in graphene. The scale of local heterojunction fabrication is about 1 μm. We observe that with an increasing of the laser fluence the number of defects increases according to two different mechanism for low and high fluences, respectively. The change of the charge carrier concentration causes the Dirac point shift in produced structures. We investigate the photoresponse in graphene junctions under fs pulsed laser irradiation with subthreshold energies. The response time is rather high while relaxation time is large because of charge traps at the graphene/SiO₂ interface.

A strong light-matter interaction is one of the most exploited features provided by plasmonic systems.1 To extend this capability beyond the visible and near-infrared regimes, using low-loss materials is a major goal in current nanophotonics research.2 Polar dielectric crystals, such as silicon carbide (SiC), can provide sub-diffraction confinement of mid-infrared and terahertz radiation with mode volumes and quality factors exceeding the best case scenario attained by plasmonic counterparts.3, 4 This makes these materials extremely sensitive to minute changes in the ambient environment and also strong candidates for resonant surface-enhanced spectroscopy in the infrared (SEIRA).5, 6 We report on the behaviour of surface phonon polariton (SPhPs) resonances of SiC nanopillar arrays upon their coverage with sub-nanometric and nanometric alumina (Al2O3) and zirconia (ZrO2) thin films. Highly conformal and uniform oxide layers were obtained through atomic layer deposition (ALD) and measurements of SPhP modes were performed using Fourier transform infrared spectroscopy (FTIR) in reflectance mode. Concurrent anomalous red and blue shifts of SPhP resonances were observed upon Al2O3 deposition, with shift direction being dictated by their relative position to the ordinary longitudinal optic (LO) phonon the thin film. The concurrent shifts, attributed to the coupling to the Berreman mode of the dielectric layer, persisted for thicker films and are shown to be correctly predicted by numerical calculations using the measured permittivity of the deposited oxide. On the other hand, the deposition of sub-nanometric layers of ZrO2 lead to anomalous blue-shifts of transverse and longitudinal SPhP resonances around 900cm-1, a behaviour which persisted for layers up to ≈1.5nm in thickness, and reversed to the canonical red-shift expected for a dielectric screening of resonances when the pillars were covered with thicker layers. These anomalous shifts could not be reproduced numerically by employing the measured permittivity of the films and provide evidence for a localized surface state, which when modelled as a simple Lorentz oscillator, provide semi-quantitative agreement with experimental results. In addition, the predictive red-shifts obtained for thicker films may provide a tool for real-time monitoring of thin-film growth. This work demonstrates the potential of low-loss phonon polariton systems and offers new prospects to near-field based ultra-sensitive chemical sensing and to the field of nanophotonics. 1. Maier, S. A., [Plasmonics: Fundamentals and Applications.] 1st ed.; Springer US: NY, (2007). 2. Caldwell, J. D.; Lindsay, L.; Giannini, V.; Vurgaftman, I.; Reinecke, T. L.; Maier, S. A.; Glembocki, O. J., "Low-loss, infrared and terahertz nanophotonics using surface phonon polaritons." Nanophotonics, 4 (1), 44-68, (2015). 3. Caldwell, J. D.; Glembocki, O. J.; Francescato, Y.; Sharac, N.; Giannini, V.; Bezares, F. J.; Long, J. P.; Owrutsky, J. C.; Vurgaftman, I.; Tischler, J. G.; Wheeler, V. D.; Bassim, N. D.; Shirey, L. M.; Kasica, R.; Maier, S. A., "Low-Loss, Extreme Subdiffraction Photon Confinement via Silicon Carbide Localized Surface Phonon Polariton Resonators." Nano Letters, 13 (8), 3690-3697 (2013). 4. Gubbin, C. R.; Maier, S. A.; De Liberato, S., "Theoretical investigation of phonon polaritons in SiC micropillar resonators." Physical Review B, 95 (3), (2017). 5. Anderson, M. S., "Enhanced infrared absorption with dielectric nanoparticles." Applied Physics Letters, 83 (14), 2964-2966, (2003). 6. Neubrech, F.; Huck, C.; Weber, K.; Pucci, A.; Giessen, H., "Surface-Enhanced Infrared Spectroscopy Using Resonant Nanoantennas." Chemical Reviews, 117 (7), 5110-5145, (2017).

We propose octagonal quasi-crystal designs providing effective light confinement for different resonance frequencies through the structural modification with the utilization of low-symmetric photonic unit cells. The effect of rotational symmetry reduction on the cavity resonance appearing in the corresponding photonic bandgap of each structure has been investigated. Relatively small dielectric cylinders have been additionally located at discrete angular positions with particular distances from the center of the each core cylinder and the noteworthy resonance peaks have been observed to emerge in the bandgaps. Rotational symmetry of the proposed structures is to be modified by varying the angular displacement of the smaller quasi-crystalline rods with the angle θ in terms of the x-axis of the small rod. The successful demonstration of tunable resonance modes has been achieved numerically and experimentally for the first time by tailoring the positional parameters and reducing the crystalline symmetry. Strongly localized modes in the proposed quasi-crystals have great potential for various slow light applications along with other technologies such as sensors, lasers and memory units.

We pursue a nanophotonic platform for strong light-matter interaction that combines plasmonic mode volumes, i.e., deep subwavelength confinement, with cavity quality factors (Q = 1000 to 100000). To this end we study the physics of resonator structures in which plasmon antennas are placed inside microcavities, like microdisks and photonic crystal cavities. Coupled oscillator theory for the local density of optical states in such systems shows a rich family of Fano-type line shapes, meaning that interferences lead to both transparency windows (very low LDOS, even when both antenna and cavity are separately on resonance) and to Purcell factors that far exceed those of antenna and cavity alone. These results are further confirmed by full-wave modelling. We will report experiments that probe the system from several viewpoints. First, we show that it is not true, even for high-Q cavities, that plasmon scatterers necessarily reduce Q, as evident from probing the cavity response in an experiment where we approach a cluster of plasmon nanorods to a microtoroid with a Q of 10^6. Second, we show that the polarizability of an antenna is strongly dependent on whether it is coupled to a microcavity, as evident from antenna extinction in the same experimental system. Thirdly, we show that in Si3N4 microdisk-antenna structures made by lithography that we decorate with single nanoantennas as well as phased arrays, dominantly plasmonic modes can be obtained even at Q’s well above 10.000. The richness of the physics that is evident from the experiments clearly goes well beyond simple perturbation models. The underlying mechanism is that both the cavity and the antenna are essentially open systems that have radiation as their main loss mechanism. Interaction and interference through these radiative channels leads to unexpected performance characteristics for light-matter interaction that in terms of coupled mode theory map on non-hermitian coupled oscillator properties. We believe that this can be captured by casting the problem in language of Quasi-Normal Modes. Our current efforts are devoted to matching these systems to near-infrared quantum emitters such as dibenzo-terrylene in anthracene for low-temperature quantum optics studies.

Hybrid nanomaterials are targeted by a rapidly growing group of nanooptics researchers, due to the promise of optical behavior that is difficult or even impossible to create with nanostructures of homogeneous composition. Examples of important areas of interest include coherent coupling, Fano resonances, optical gain, solar energy conversion, photocatalysis, and nonlinear optical interactions. In addition to the coupling interactions, the strong dependence of optical resonances and damping on the size, shape, and composition of the building blocks provides promise that the coupling interactions of hybrid nanomaterials can be controlled and manipulated for a desired outcome. Great challenges remain in reliably synthesizing and characterizing hybrid nanomaterials for nanooptics. We review and describe the synthesis, characterization, and applications of new hybrid plasmonic nanomaterials that are created through plasmon-induced photopolymerization. Involved polymer can contain active species, resulting in advanced hybrid nano-emitters The work is placed within the broader context of hybrid nanomaterials involving plasmonic metal nanoparticles and molecular materials placed within the length scale of the evanescent field from the metal surface. We specifically review three important applications of free radical photopolymerization to create hybrid nanoparticles: local field probing, photoinduced synthesis of advanced hybrid nanoparticles (including light-emitting nanosystems), and nanophotochemistry. We first demonstrate that nanoscale photopolymerization is possible at the surface of Ag nanoparticles,1,2 gold nanocubes3 and within the gap between two coupled metal nanoparticles.4 This local polymer integration enables symmetry breaking, quantification of plasmonic near-fields and trapping of molecules whose Raman signature gets amplified. Secondly, we show that it is possible to integrate quantum nanoemitters in the vicinity of plasmonic nanostructures with high spatial precision via two-photon polymerization. 5 In particular, we demonstrate two-color nanoemitters that enable the selection of the dominant emitting wavelength by varying the polarization of excitation light. The nanoemitters were fabricated by using two polymerizable solutions with different quantum dots, emitters of different colors can be positioned selectively in different orientations in the close vicinity of the metal nanoparticles. The dominant emission wavelength of the metal/polymer anisotropic hybrid nanoemitter thus can be selected by altering the incident polarization. 1. Phys. Rev. Lett. 98, 107402 (2007) 2. ACS Nano 4, 4579 (2010) 3. J. Phys. Chem C. 116, 24734 (2012) 4. ACS Photonics 2, 121 (2015) 5. Nano Letters 15, 7458 (2015)

When two sub-wavelength metallic nanoparticles, each of them supporting a resonant plasmon, are brought within few nanometers or less from each other, the two plasmonic resonances are strongly coupled. The new eigenmodes of the system include in particular a dipolar mode, for which the maximum electric field is localized in the nanoscale gap between the particles. The local field enhancement compared to the incoming far field can be several hundred folds. We present the design and fabrication of such plasmonic gap cavities, created by depositing gold nanospheres on an atomically flat gold surface, which has been functionalized with a self-assembled monolayer of thiol molecules. This system enables extremely large and reproducible enhancement of the Raman signal from the molecules. Although these nanogap cavities have been used in SERS studies for some time already, a detailed understanding of the out-of-equilibrium physics under laser irradiation is missing. What is the local temperature of the electrons in the metal? Is the molecular vibration in equilibrium with the surrounding thermal bath? We will present our latest results in the spectroscopy of these nanocavities under broadly tunable excitation. In particular, we want to clarify if a suitable detuning of the laser from the plasmonic resonance can lead to amplification of molecular vibrations [1] well above the thermal occupancy. [1] P. Roelli et al, Nature Nanotechnology 11, 164–169 (2016)

A dynamic all-optically controlled surface plasmon polartions (SPP) novel high-performance multi-function optical microscope, combining optical microscopic imaging, bio-sensing and surface enhanced Raman Scattering (SERS) in a single microscopic system, is presented in this talk. This new configuration uses phase shift of SPP standing wave generated from sub-wavelength slit arrays embedded in a thin metal film to achieve super-resolution wide-field microscopic imaging; phase sensitive surface plasmon resonance (pSPR) bio-sensing technology based on differential phase measurement between radially polarized (RP) and azimuthally polarized (AP) beams to obtain an ultra-high sensitivity and a wide dynamic range simultaneously; the coupling between the localized surface plasmon (LSP) of metallic nano-particles and SPP virtual probe with longitudinal electric field to significantly improve the sensitivity of SERS system. With the integration of these three technologies in a single microscopic configuration, the system can achieve wide-field super-resolved imaging of biological specimens, ultra-high sensitivity for molecule detection and real-time monitoring for reaction process of biological samples simultaneously, fulfilling the requirement of multi-parameter multi-function real-time in-situ measurement of biological samples. The new microscopic scheme has great importance in real-time dynamic study on nano-scale biological living cells as well as accurate near field mapping.

In the past few years, silicon nitride planar waveguides have become a reference platform for nonlinear nanophotonics, especially for Kerr frequency comb generation but also for spectral broadening and supercontinuum generation. In this work, we present several spectral broadenings using waveguides with different group velocity dispersion, some of them reaching a full octave span. By means of an innovative hyperspectral near-field microscopy technique, we fully characterize the spectral change that occurs during the propagation of light in the waveguide. Optical near-field microscopy allows the mapping of the electromagnetic field with a resolution down to a few tens of nanometers, below the diffraction limit. Such a resolution is achieved by collecting the evanescent and propagative fields using a dielectric probe made out of a tapered optical fiber whose extremity has a 50-nm diameter. While this technique has traditionally been used in linear optics with only one or a few wavelengths, it has recently been extended to the mapping of the optical spectrum using a spectrometer and a fast camera. In this work, we use both a visible CCD camera and an InGaAs camera for infrared measurements around the pump wavelength at 1550 nm. The pump laser is a 100-fs pulsed laser source with a peak power of about 30 kW. An hyperspectral measurement consists in recording the optical intensity for each position (x,y) on the sample and for each wavelength: a 3D matrix P(x,y,\lambda) is therefore obtained. From this raw data, several representations can be made. The spectra can be compared from point to point, when following the waveguide, allowing to better understand the nonlinear processes at stake during the supercontinuum generation. In particular, we show that depending on the width of the waveguide, the spectral broadening is qualitatively different owing to the different regimes of dispersion. Our setup allowed us to measure the spectrum evolution on 1 cm of propagation, leading to an octave-spanning spectrum in the case of an anomalous-dispersion waveguide. In this case, spectral feature such as dispersive waves, third-harmonic generation and self-phase modulation give very clear and obvious signatures. Hyperspectral near-field imaging also allows to image the multi-mode propagation within larger waveguides. In the case of spectral broadening in such waveguides, different spatial modes participate to the propagation and are differently visible depending on the wavelength. Clear interference patterns can be visualized using false-color imaging representations. This technique would provide much needed characterization for the emerging nonlinear optics in multimode waveguides research area.

Transformation optics is a general design tool that is as intuitive as the ray optics, but exact at the level of Maxwell’s equations. It provides a direct link between a desired electromagnetic phenomenon and the material response required for its occurrence. In this talk, I will give an overview of some recent progress of transformation optics, with a special focus on its applications at the subwavelength. 1. I will show how to use this strategy to design a finite subwavelength particle that can harvest light over a broadband spectrum like an infinite plasmonic system; 2. I will discuss how the conformal transformation approach can help us understand some complex plasmonic phenomena, such as fast electron interaction with singular plasmonic particles, van der Waals interaction at extreme scales, compact dimensions in 2D singular plasmonic surfaces, etc.

A three dimensional rigid spherical microscopic object can rotate in either the pitch, yaw or roll fashion. Among these, yaw motion has been conventionally studied using the intensity of the scattered light from birefringent microspheres through crossed polarizers. So far, however, there is no way to study the pitch rotational motion in spherical microspheres. Here we suggest a new method towards the study of such pitch motion in birefringent microspheres under crossed polarizers by measuring the 2-fold asymmetry in the scattered signal using video microscopy. We show a simple example of pitch rotation determination using video microscopy for a microsphere attached with a kinesin molecule while moving along a microtubule. It can also be extended to optical tweezers.

We propose and demonstrate experimentally an optical analogue of the famous Archimedes' screw where airborne particles are conveyed down or upstream the photons momentum ow through the rotation of a helical optical beam. We also report on the action of such a rotating screw on low-absorbing particles in a solution.

Dielectric nanoparticles, and silicon nanoparticles in particular [1,2], are becoming increasingly promising for various applications in photonics, nonlinear optics, optomechanics, and medicine. Plenty of applications exploit the benefits of low-loss Mie resonances, exhibited in the optical range by silicon nanoparticles with sizes of the order of 200 nm. The frequencies of the resonant Mie modes are determined by the size and shape of the particles. However, many of the fabrication techniques result in a polydisperse mixture of different sizes and shapes, and prompt for a post-processing to provide a uniform output. Having an entirely optical tool for such separation [3,4] is highly desirable for sterile, hazardous or highly dynamic microfluidic environments. Following our recent publication [4], in this contribution we present the calculated optical forces acting on silicon nanoparticles in aqueous environment, analyse their potential for optical sorting in a number of schemes, and discuss the experimental implementation of the proposed methods in our setup. The optical forces acting on silicon nanoparticles are shown to reveal their substantial dependence on the particle size. This dependence results in different velocities of the light-driven drift of the nanoparticles, depending on their size and the frequency of the incident light. We propose to employ these features to realise optical sorting, according to the following scenarios. First, we use two counter-propagating beams of different wavelength, which move particles of different sizes in opposite directions; by varying the intensity ratio between the two beams, different subsets of the particle sizes can be separated. A similar approach has been implemented for plasmonic particles [3]. Second, we suggest to impose two counter-propagating beams upon a uniform flow of a disperse mixture, which results in the particles of different sizes being pushed along different directions in space, so that an efficient angular separation is possible within certain size ranges. Third, we propose an efficient angular separation in an all-optical way, by directing the two beams at an angle. This scenario offers an efficient angular separation without any imposed flow. In this work, we consider two laser beams with wavelengths of 532 and 638 nm. For this particular case, angular sorting scheme provides a unique size-angle dependence, yielding up to 70° span of deflections, in the size ranges of 120–160 nm, 190–220 nm, and a few smaller sets. We demonstrate that the proposed angular sorting techniques are robust against the Brownian motion, requiring a run of about 100 μm to achieve a 10-nm distinction in size, while using moderate (0.1 W) power. Finally, we consider the forces acting on silicon nanoparticles in the evanescent wave illumination and show that the proposed methods can be applied for a broad size dimensions using p-polarised light. [1] Evlyukhin A.B., et al. Nano Lett. 12, 3749–3755 (2012). [2] Kuznetsov A.I., et al. Sci. Rep. 2, 492 (2012). [3] Ploschner M., et al. Nano Lett. 12, 1923–1927 (2012). [4] Shilkin D., et al. ACS Photonics 4, 2312–2319 (2017).

The negatively charged nitrogen vacancy centre in diamond is known for its coherent spin properties and optical interface, and thus is regarded a promising candidate for quantum information applications [1]. Realisation of an efficient spin-photon interface with the NV centre is made challenging however by the fact that, in bulk diamond, only 3-4% of spontaneously emitted photons occur in the zero phonon line (ZPL). Placing NV centre in an optical cavity is being explored by several groups [2][3][4] as an effective way to selectively enhance the coherent emission of NVs and thereby increase the efficiency of the coherent spin-photon coupling. Previous work reported successful coupling of the NV in nano-diamond to an open access micro-cavity and observed enhanced ZPL emission [5]. However the NV centres in nano-diamond suffer from broadened zero phonon transition and poor spin coherence. By fabricating NV centres in a ~micrometre thick membrane of high purity single crystal material we can take advantage of the tunability of open access cavities, and at the same time, provide close-to-bulk crystal environment to maintain the coherent spin properties of the NV centres. Here we report our work on the tunable cavity coupling of the ZPL of a NV centre in a 1.2micrometre-thick diamond membrane at 4K. The diamond membrane is fabricated from a 0.5mm-thick E6 CVD diamond plate where ion implantation is carried out on both surfaces to create NV centres at the depth of around 70nm. The plate is then machined into 30micrometre-thick slices, and thinned by ICP-RIE with a combination of Ar/Cl[6] and pure oxygen plasma etching recipes. The open cavity consists of a concave mirror (99.99% reflectivity) deposited on a template fabricated using Focused Ion Beam (FIB) milling[7] and a planar mirror (99.8% reflectivity) which supports the membrane. For bare cavities with mirror radii of curvature (RoC) of 12micrometre, we measured a finesse of F~2000 and mode volume as small as 0.75micrometre^3. In-situ tuning of the cavity resonance is achieved with piezoelectric actuators. When mounted in our bath cryostat the cavity modes have dominant Lorentzian line profiles which indicate a passive stability of the cavity length of better than 0.15nm. No active locking is currently deployed. With the presence of a diamond membrane inside the cavities, the measured finesse and mode volume of a cavity with 12micrometre RoC are found to be around 300 and 3 micrometre^3, respectively. We attribute the reduction in finesse to scattering at the membrane-air and membrane-mirror interfaces. On coupling to the ZPL of a target NV centre, we record a factor of 4 increase in the saturated intensity of ZPL fluorescence compared to that measured from the same NV centre in absence of the concave mirror. This result is consistent with the calculated Purcell factor of 16 combined with a relatively low efficiency of light extraction (estimated to be around 19%) from the cavity due to the scattering losses.

We report on the optical properties of recently developed telecom-wavelength quantum dots based on the GaAs material system. In order to achieve the InAs quantum dot wavelength shift towards the telecom C-band, strain-relaxation with the help of an InGaAs metamorphic buffer is realized. The general emission properties of the quantum dot ensemble and single dots is analyzed, containing analysis of lifetime measurements and fine-structure splitting investigations. Single-photon emission is verified for excitation in continuous wave and pulsed mode. The generation of polarization-entangled photon pairs via the biexciton-exciton radiative cascade is shown, even for increasing time windows and time delays.

Metamaterials are artificial subwavelength structures. By altering energy-momentum dispersion, metamaterial allows a control of photophysical property of emitters located nearby. Furthermore, the presence of plasmonic layers in composition of metamaterial permits an image-dipole interaction. It will be examined how a series of photophysical properties including charge transfer in donor-acceptor structure and spectral shift of intramolecular charge transfer emitters are modified nearby metamaterials.

Polarized time resolved fluorescence measurements are used to characterise the structure of the two-photon tensor in the enhanced green fluorescent protein (EGFP) and predict the “hidden” degree of hexadecapole transition dipole alignment 〈α₄₀〉 created by two-photon absorption (TPA). We employ a new method for the accurate STED measurement of the evolution of 〈α₄₀〉 by analysing the saturation dynamics of the orthogonally polarized components of two-photon excited EGFP fluorescence as a function of the time delay between the 800 nm pump and 570 nm dump pulses. The relaxation of 〈α₄₀〉 by homo-FRET is found to be considerably greater than that for the fluorescence anisotropy which directly measures the quadrupolar transition dipole moment alignment 〈α₂₀〉. Our results indicate that higher order dipole moment correlation measurements promise to be a sensitive probe of resonance energy transfer dynamics.

Semiconductor quantum dots (QDs) are a promising “nano-antennas” capable of absorbing efficiently light energy upon one- or two-photon excitation and then transferring it to convenient energy acceptors via Förster resonance energy transfer (FRET). The photosensitive protein bacteriorhodopsin (bR) has been shown to be a promising material for optoelectronic and photovoltaic applications, but it cannot effectively absorb light in the UV, blue, and NIR regions. It was shown previously that formation of hybrid complexes of QDs and purple membranes (PMs) containing bR could significantly improve the bR capacity for utilizing light upon one- and two-photon laser excitations. Under the laser irradiation, the optical properties of bR itself remain unchanged, whereas those of QDs may be altered. Therefore, it is important to study the effects of intense laser excitation on the properties of the QD–PM hybrid material. In this study we have shown that laser irradiation can lead to an increase in the luminescence quantum yield (QY) of QDs. The fact that this irradiation does not change the QD absorption spectra means that the QD quantum yield may be optically controlled without changing the QD structure or composition. Finally, we have shown experimentally that photoinduced increase in the QY of QDs lead to the corresponding increase in the efficiency of FRET in the QD–PM hybrid material. As a result, an approach to increasing the FRET efficiency in hybrid nano-biomaterials where QDs serve as donors have been proposed.

The issue of whether the optical orbital angular momentum of light can play any significant role in chiroptical interactions has seen a resurgence of interest in the past few years. Revising preliminary expectations, it has been shown both theoretically and experimentally that the topological charge can indeed play a decisive role in some chiroptical interactions, with the rates of these optical phenomena proving sensitive to the sign of the vortex charge ℓ. Using quantum electrodynamics, it is now revealed how the inclusion of molecular electric-quadrupole transition moments in both chiral and achiral anisotropic media produces such an effect. Specifically, for single-photon absorption it transpires that both the orbital and spin angular momentum must be engaged through a circularly polarized vortex beam. The chiroptical effect is identified as a manifestation spin-orbit interaction in light.

The capacity to tailor as wanted the fluorescence’s properties of a fluorophore increases the number of applications were the same fluorophore can be useful, like in imageology. One way to modify these properties is the presence of plasmonic fields nearby the fluorophore, and their origin can be the surface plasmons generated in metallic nanoparticles, like silver and gold, when these are excited. Usually fluorescence quantum yield is studied by conventional fluorescence spectroscopy techniques, but these are subjected to errors from reflection or refraction from the sample and a way to avoid these errors is to use indirect measurements techniques as in the case of thermal lens spectroscopy, which measures the change generated by the sample’s absorption of radiation, instead of measuring the absorption per se as regular spectroscopic methods. This technique is based in the photoinduced refraction index’s change. In this work we studied the effect that silver nanoparticles had in the fluorescence’s properties of ethanolic solutions of rhodamine B, specially its quantum yield, using a mode-mismatched thermal lens setup. We found that the presence of silver nanoparticles lowers the dye’s quantum yield between 4% and 38% which depends on the dye and nanoparticles’ concentrations. The thermal diffusivity’s values showed that the silver nanoparticles are increasing the non-radiant decay velocity of the rhodamine b, which is the reason why the quantum yield gets lower. These results not only gave us information about the studied samples, but also validate the capacity of a mode-mismatched thermal lens system to study fluorescence properties.

The molecular clusters, so called J-aggregates of pseudoisocyanine dye, were obtained in ordered cylindrical nanopores of anodic aluminum oxide. The absorption and luminescence of the samples were studied by the VIS-spectroscopy and laser confocal microscopy. The band of J-aggregates has the same shape, but is inhomogeneous broadened in comparison with solution. The luminescence maximum of J-aggregates was observed at 578 nm upon excitation at 543 nm as well as at 405 nm. Non-resonant luminescence excitation occurred due to energy transfer from oxygen vacancy of alumina to molecular nanoclusters. This is also confirmed by time-resolved luminescence spectroscopy, which shows the increase of luminescence decay time of J-aggregates placed in alumina up to the luminescence time of the clean alumina in comparison with J-aggregates coated on glass substrate.

As a class of semiconductors, transition metal dichalcogenides (TMDs) have the formula MX2, where M stands for a transition metal (i.e., Mo, W, Ti, Nb, etc.) and X stands for a chalcogen (i.e., S, Se or Te). TMDs show graphene-like layered structure. Strong covalent bonds in layers and weak van der Waals interaction between layers allow TMDs to form a robust 2D nanostructure. In a TMD monolayer, the single transition metal layer is sandwiched between the two chalcogen layers. Owing to the specific 2D confinement of electron motion and the absence of interlayer coupling perturbation, 2D layered TMDs show unique photonics-related physical properties, e.g., 1) Sizable and layer-dependent bandgap, typically in the 1-2 eV range; 2) Indirect-to-direct bandgap transition as the decreasing of the number of monolayer; 3) Fairly good photoluminescence and electroluminescence properties; 4) Remarkable excitonic effects, i.e., high binding energy, large oscillator strength and long lifetime. In combination of the ultrafast carrier dynamics and molecular-scale thickness, the prominent properties manifest the 2D TMDs a huge potential in the development of photonic devices and components with high performance and unique functions. We have extensively studied the ultrafast nonlinear absorption and nonlinear refraction of layered MX2 (X=S, Se, Te) over broad wavelength (Vis-NIR) and time (fs-ps-ns) ranges. Large area MoS2 neat films with controllable thicknesses were fabricated from liquid-exfoliated MoS2 dispersions by vacuum filtration. The MoS2 films show superior broadband ultrafast saturable absorption (SA) performance, in comparison with the graphene films and the MoS2 dispersions. Very recently, we observed giant two-photon absorption (TPA) coefficient in a WS2 monolayer. The order of magnitude of TPA coefficient in WS2 monolayer (~100 cm/MW) exceeds that of the conventional semiconductors (e.g., CdTe, GaAs, ZnS, ZnO, etc.) by a factor of 3-4. This is also the first Z-scan performance on an optical medium with a thickness as tiny as 0.75 nm. Moreover, a comprehensive study on the layer-dependent nonlinear photonic effect was carried out in MoS2 mono- and few-layers by CVD growth. SA to TPA transition was confirmed when the thickness changes from few-layer to monolayer. In addition, a spatial self-phase modulation method has been applied to tune the nonlinear refractive index of TMD dispersions. The above-mentioned works have opened up a door towards 2D semiconductor based nonlinear photonics, spectroscopy and relevant photonic devices.

High-harmonic generation (HHG) in condensed-matter systems is both a source of fundamental insight into quantum electron motion and a promising candidate to realize compact ultraviolet and ultrafast light sources [1-3]. Here we argue that the large light intensity required for this phenomenon to occur can be reached by exploiting localized plasmons in conducting nanostructures. In particular, we demonstrate that doped graphene nanostructures combine a strong plasmonic near-field enhancement and a pronounced intrinsic nonlinearity that result in efficient broadband HHG within a single material platform [4]. We extract this conclusion from time-domain simulations using two complementary nonperturbative approaches based on atomistic one-electron density matrix and massless Dirac-fermion Bloch-equation pictures, where the latter treatment is supplemented by a classical electromagnetic description of the self-consistent field produced by the illuminated nanostructure. High harmonics are predicted to be emitted with unprecedentedly large intensity by tuning the incident light to the localized plasmons of ribbons and finite islands. In contrast to atomic systems, we observe no cutoff in harmonic order, while a comparison of the predicted HHG from graphene to that observed in solid-state systems suggests that the HHG yields measured in semiconductors can be produced by graphene plasmons using 3-4 orders of magnitude lower pulse fluence. Our results support the strong potential of nanostructured graphene as a robust, electrically-tunable platform for HHG. [1] S. Ghimire et al., “Observation of High-Order Harmonic Generation in a Bulk Crystal,” Nat. Phys. 7, 138 (2011). [2] O. Schubert et al., “Sub-Cycle Control of Terahertz High-Harmonic Generation by Dynamical Bloch Oscillations,” Nat. Photon. 8, 119 (2014). [3] T. T. Luu et al., “Extreme Ultraviolet High-Harmonic Spectroscopy of Solids,” Nature 521, 498 (2015). [4] J. D. Cox, A. Marini, and F. J. García de Abajo, “Plasmon-Assisted High-Harmonic Generation in Graphene,” Nat. Commun. 8, 14380 (2017).

Chirality is a general phenomenon in nature. Many biomolecules in our body such as DNA and enzymes are chiral. The enantiomers existing in oranges and lemons cause different smells. More importantly, while one chirality forms a powerful medication, the other may cause very serious side effects, for instance in the case of left- and right-handed Thalidomide. It is hence of crucial significance to understand chirality for the purpose of interpreting chirality in biology as well as employing chirality for sensing applications in chemistry, pharmacy, etc. Chiral plasmonics holds great potential in the sense that it has a large range of flexibility to mimic natural chiral substances and simultaneously exhibits a giant chiroptical response arising from the strongly confined and enhanced electro-magnetic field. Nonlinear chiral plasmonics is even more desired since the nonlinear chiroptical effects might be orders of magnitude higher than their linear counterparts. Until now, both linear and nonlinear chiroptical properties in tailored chiral plasmonic systems have been investigated. However, the underlying physical mechanism for nonlinear plasmonic chirality is far from being understood and further quantitative modelling is particularly missing. Here we study the third-order chiroptical responses of a 3D chiral structure consisting of identical corner-stacked gold nanorods, the so-called plasmonic Born-Kuhn analog. The structures were fabricated by a multi-layer electron-beam lithography (EBL) technique. First, the glass substrate was covered by a dielectric spacer layer (IC1-200, Futurex) via spin-coating. Second, EBL processing procedures (electron-beam exposure of a PMMA resist, development, evaporation of a gold film, and subsequent lift-off) were implemented to fabricate one layer of gold nanorods. The rod lengths were varied to tune the plasmonic resonances in the range of 920-1150 nm, which match the spectral window of our ultrafast laser source. Third, another IC1-200 spacer layer was spin-coated above the layer of gold nanoantennas. Fourth, employing a second EBL cycle assisted by precise positioning, the second layer of gold nanorods was finished. Finally, a third IC1-200 spacer layer was planarized on top in order to create isotropic environment for the gold nanostructures. The thickness of the IC1-200 spacer layer was selected to ensure strong coupling via optical near-field between the two layers of gold nanorods. A C4 geometrical symmetry was designed to eliminate linear birefringence in the structures. A home-made wavelength-tunable laser source with 60 fs pulse duration was used as the pump for nonlinear frequency conversion. Circularly polarized fundamental light was realized by combination of a polarizer and a broadband quarter waveplate. The third-harmonic-generation signals were recorded by a CCD camera attached to a spectrometer. Nonlinear chiroptical spectroscopy was performed by tuning the wavelength and switching the handedness of the fundamental light. To interpret the nonlinear chiroptical responses, we utilized a coupled anharmonic oscillator model, in which the coupling term of the two layers of gold nanorods and the phase retardation of the incoming fundamental and outgoing generated wave are fully considered. In this way, we achieve good agreement between experimental measurement and analytical prediction. This quantitative model addresses the origin of the nonlinear chiroptical effects and is very instructive for the efficient design of plasmonic chiral structures for giant nonlinear circular dichroism. Our research extends the present understanding of chiral plasmonic systems and paves the way towards ultrasensitive nonlinear chiral sensing.

Saturable absorption (SA) is an extreme nonlinear phenomenon that consists of the quenching of optical absorption under high-intensity illumination. This effect, which is an inherent property of photonic materials, constitutes a key element for passive mode-locking (PML) in laser cavities, where continuous waves are broken into a train of ultrashort optical pulses. Most materials undergo SA at very high optical intensities, in close proximity to their optical damage threshold. Currently, state-of-the-art semiconductor-based SA mirrors are routinely employed for PML lasers. However, these mirrors operate in a narrow spectral range, are poorly tunable, and require advanced fabrication techniques. Recently, carbon nanomaterials have emerged as an attractive, viable, and cost-effective alternative for the development of next-generation PML lasers. For example, carbon nanotubes undergo SA at rather modest light intensities, while their operation wavelength (determined by the energy band gap) can be manipulated by tuning their diameter. Broadband operation has been demonstrated by using an ensemble of CNTs with a wide distribution in diameter, at the expense of higher linear loss from off-resonance tubes. Graphene overcomes this limitation thanks to its peculiar conical band structure, which gives rise to broadband resonant SA at remarkably low light intensity that can further be tuned by means of an externally applied gate voltage. Graphene-based SA components have been used to achieve PML ultrafast laser operation, broadband tunability, and quality-factor switching. Graphene multilayers have also been employed to generate large energy pulses and to achieve PML in fiber lasers with normal dispersion. In addition, recent theoretical investigations predict single-mode operation of random lasers by embedding graphene flakes in a gain medium. Here we calculate intraband and interband contributions to SA of extended graphene by nonperturbatively and semianalytically solving the single-particle Dirac equation for massless Dirac fermions (MDFs) in the presence of an external electromagnetic field retaining only one-photon processes. We further investigate the dependence of the intensity-saturated grapheme conductivity on doping, temperature, and optical frequency. Interestingly, we find a remarkably low intensity threshold for SA, which is consistent with available experimental reports. Our calculations indicate a strong quenching of absorption depth produced by electrical doping (which can be controlled through gating), as well as a weak dependence on electron temperature. Additionally, through time-domain simulations based on an atomistic tight-binding/single-particle density-matrix formalism, we study SA in graphene nanoribbons, including finite-size effects and electron-electron interactions that play a significant role in the optical response of nanostructured graphene. Surprisingly, we find that while the linear absorption predicted in atomistic simulations is reduced compared to that of extended graphene, its nonlinear saturation intensity threshold is in good quantitative agreement with predictions based on the MDF model. Deviations from the semianalytical treatment occur only at high doping, where SA is quenched and multiphoton processes lead to an intensity-dependent increase of absorption. We anticipate that the present findings will impact the future development of graphene-based PML fibre lasers and single-mode random lasers.

We propose and demonstrate photonic crystals (PCs) providing backward-directional propagation of surface slow waves, which is significant for potential PC-based photonic applications. An effective pathway for backward directing of surface slow light along with the modification of other important characteristics is presented via implementing surface morphological diversity in PCs. With the surface orientation angle varying from 900 to 300, the newly appearing bands inside the band gap shift to higher frequencies, and negative group indices up to -100 are observed as the strong indication of backward propagation. Furthermore, dependence of the propagation direction on the surface corrugation angle has been verified via detailed time-domain analyses and microwave experiments using dipole source. As obtained from both the numerical and experimental results, for instance, the structure with 600 provides a well-defined backward propagation. In addition, normalized-delay-bandwidth-product can easily be modified by varying the surface orientation angle in the proposed structures according to the necessities of the application. Furthermore, the group velocity dispersion spectra extracted for each periodic structure exhibit considerably high-range near-zero values as 0.139 ps²/m at 900 for the range of 495.54-501.25 nm and 0.176 ps²/m at 85° for the range of 495.66-501.25 nm. Third order dispersion spectra also obtained for the proposed PCs show near-zero values as 0.098 ps³/m at 900 and 0.113 ps³/m at 85° in the corresponding frequency regimes. Facile control of the key characteristics such as backward-directed surface wave propagation in the periodic dielectric structures having morphological diversity serves a great potential for nextgeneration photonic applications.

Orbital angular momentum is a fundamental degree of freedom of light that manifests itself even at the single photon level. The coherent generation and beaming of structured light usually requires bulky and slow components. Using wave singularities known as bound states in continuum, we report an integrated device that simultaneously generates and beams powerful coherent beams carrying orbital angular momentum. The device brings unprecedented opportunities in the manipulation of micro-particles and micro-organisms, and, will also find applications in areas such as biological sensing, microscopy, astronomy, and, high-capacity communications.

Josephson dynamics, spontaneous symmetry breaking and quantum criticality are fascinating physical phenomena that can be realized today in coupled dissipative optical cavities with nonlinear interactions. Among the different experimental test-beds, photonic crystal coupled nanocavities operating in the laser regime are outstanding systems since nonlinearity, gain/dissipation and intercavity coupling can be judiciously tailored [1]. Complex photon statistics is inherent to the nature of nanolasers due to the presence of strong spontaneous emission noise. Yet, although most common scenarios emerge from quasi-dynamical equilibrium where the gain nearly compensates for losses, little is known about far-from-equilibrium statistics resulting, for instance, from a rapid variation of a parameter or "quench". Our nanolasers are fabricated in suspended 2D InP-based Photonic Crystal membranes, and studied as a function of pump power and coupling strength. The modification of coupling strength is obtained by an original engineering procedure that allows us to tune the coupling strength between the nanocavities without affecting the nanolaser performance [1]. Under short (100 ps) pulse pumping, the strongly coupled laser nanocavity system exhibits two modes: a strong lasing mode, which has an anti-symmetric energy distribution, and a weak nonlasing one, possessing a symmetric energy distribution. We implement a simple experimental technique –single pulse energy detection scheme– that allows us to measure the statistical distributions of the photon number of both modes simultaneously. In particular, we analyze the photon number distributions of the weak one and link, using a mean field model, both the emergence of fat tails in the distributions and the superthermal nature of the emission through second order correlation (g2) measurements. We conclude that transient dynamics after quench, when projected onto the nonlasing mode, generically exhibit long-tailed superthermal light. Such an optical quench mechanism is akin to the fast cooling of a suspension of Brownian particles under gravity, with the inverse temperature of the reservoir playing the role of the intracavity intensity. We show that passing through the lasing threshold corresponds to an abrupt decrease of the contribution of spontaneous emission —that plays the role of an effective temperature— during which the statistics of the nanolaser trajectories in phase space are dominated by nonlinear transport. Probability density functions enabled the experimental quantification of the distance from thermal equilibrium –and hence the degree of residual order– via the thermodynamic entropy. This allowed us to further detect mixing of thermal states and coherent broken parity phases, which are beyond the simple Brownian particle description [3]. REFERENCES 1. Hamel, P., et al., “Spontaneous mirror-symmetry breaking in coupled PhC nanolasers,” Nat. Phot., Vol. 9, 2015. 2. Marconi, M., et al., “Asymmetric mode scattering in strongly coupled photonic crystal nanolasers,” Optics Letters, Vol. 41, 5628, 2016. 3. Marconi, M., et al, “Quenched phases in strongly coupled dissipative optical cavities. ” arXiv preprint arXiv:1706.02993.

Nanophotonic components operate in the few-photon regime, thus their experimental characterization calls for photon-counting techniques, at least in the threshold region, and requires adequate laser models to interpret the observations. While the photon statistics of (macroscopic) Class A [1] lasers is well understood and can be readily reconstructed from the zero-delay second order autocorrelation (g(2)(0)), the memory effects introduced by the slow material response of semiconductor-based devices (Class B [1]) and the sensitivity of nanolasers to spontaneous emission [2] require a more careful approach. The latter induces a spontaneous spiking dynamics [3], near threshold, resulting in values of g(2) larger than those expected even for a chaotic signal, and growing without bounds as the duration of the spikes decreases. Currently available laser models appear unable to predict such a behaviour, due to an inadequate treatment of the contribution of spontaneous emission, and, since the Probability Density Function (PDF) collects into a statistical distribution the state of the system, its predictions fail when the dynamics is not reproduced by the model from which it is derived. Thus, contrary to the usual assumption, the validity of the photon statistics of macroscopic Class B devices [4] must be reconsidered as the cavity volume is reduced. We investigate the influence of the cavity size on a commercial VCSEL microlaser with a moderate fraction of spontaneous emission coupled into the lasing mode (beta~0.0001), which represents a happy compromise between a large enough cavity size to detect the dynamics while capturing the self-spiking typical of very small lasers. The autocorrelation (g(2)(0)) is both computed from the intensity time series with a fast (10 GHz) photodetector and deduced from the measured coincidences in arrival times of a photon counting apparatus (TAC with 15 ps timing resolution) in Hanbury-Brown & Twiss (HBT) configuration. We observe values of g(2)(0) up to 2.2, which would produce exponentially decaying distributions if interpreted through the current models [4]. Instead, the experimental PDF, reconstructed from the time series, matches the generic distributions for class B lasers even for the maximum value of g(2)(0). We therefore conclude that these two techniques cannot be considered as providing equivalent information if only the second order moment g(2) of the distribution is considered, and that new theoretical work is needed on the photon statistics of small-sized Class-B lasers. References [1]  J. R. Tredicce, F. T. Arecchi, G. L. Lippi, and G. P. Puccioni, J. Opt. Soc. Am B2, 1, 173-183, 1985. [2] G. P. Puccioni and G. L. Lippi, Opt. Express 23, 3, 2369-2374, 2015. [3] T. Wang, G.P. Puccioni, and G.L. Lippi, Sci. Rep. 5, 15858 (2015). [4] P. Paoli, A. Politi, and F.T. Arrecchi, Z. Physik B 71, 403-410, 1988.

In this work, we perform numerical studies of two photonic crystal membrane microcavities, a short line-defect L5 cavity with relatively low quality (Q) factor and a longer L9 cavity with high Q. We compute the cavity Q factor and the resonance wavelength λ of the fundamental M1 mode in the two structures using five state-of- the-art computational methods. We study the convergence and the associated numerical uncertainty of Q and λ with respect to the relevant computational parameters for each method. Convergence is not obtained for all the methods, indicating that some are more suitable than others for analyzing photonic crystal line defect cavities.

In this paper, we study the use of Titanium Nitride (TiN) as a new alternative plasmonic material to achieve a highly sensitive surface plasmon resonance (SPR) photonic crystal fiber (PCF) biosensor. The TiN has unique properties that make it an ideal material for nanofabrication, where TiN is highly stable, highly conductive, and corrosion resistant. Full vectorial finite element method is used with perfectly matched layer (PML) as boundary conditions to analyze the suggested biosensor. By analyzing the geometrical parameters of the proposed biosensor, a refractive index sensitivity of 7700 nm/RIU and 3600 nm/RIU are obtained for quasi-transverse electric (TE) and quasi transverse magnetic (TM) modes, respectively. The reported biosensor has a high linearity for detecting an unknown analyte refractive index ranging from 1.32 to 1.34. Further, fabrication of the proposed biosensor could be done using standard PCF fabrication current technologies.

We propose a novel approach in optical trapping exploiting mesoscopic photonic crystal microcavities. Full light confinement in mesoscopic photonic crystal membranes, forming a mesoscopic self-collimating 1D Fabry-Pérot cavity, was theoretically predicted and experimentally verified by the authors in previous papers. In this paper, we numerically demonstrate a high performance MPhC microcavity for optical trapping of fine particulate matter in air. The MPhC cavity has been simulated by 3D FDTD simulations while the trapping potential has been evaluated by means of the gradient force density convolution method. We numerically show that it is possible to obtain very high trapping potential for polystyrene particles having radii as small as 245 nm.

Plasmonic band gap is a range of frequencies, within which, surface plasmon polaritons cannot propagate for any wavevector. Unfortunately the first plasmonic band gap cannot be observed directly in reflectance spectroscopy [1]. To detect it, biharmonic metal-air surface structuring is conventionally utilized [2,3]. However in this case experimental geometry is strictly limited to normal angle of incidence, which is not compatible with large range of applications. In current work we introduce biperiodic plasmonic crystals. We experimentally demonstrate, that biperiodic structuring allows to tune band gap spectral-angular position. Laser interference lithography (LIL) is a well-established technique for creating periodic planar nanostructures over a large surface area. LIL allows to precisely control the modulation period and depth and thus perfectly match diffraction coupling conditions and tune plasmonic band gap properties. We used LIL experimental setup based on Lloyd interferometer. The radiation from the laser source (He-Cd, wavelength 325 nm, average power 14 mW) was spatially filtered and then formed interference pattern on the silicon wafer, covered with a thin layer of SU-8 2015. The structure period was defined by the incident angle on the interferometer. Modulation depth was defined by exposure time. By applying subsequent second exposure with another angle of incidence, we obtained biperiodic structure. Exposed samples were washed in corresponding developer, dried in air and later sputtered with 100 nm of aluminium. We fabricated a set of biperiodic plasmonic crystals with different periods and modulation depths. The quality and geometrical parameters of biperiodic plasmonic crystals were monitored by scanning electron microscopy and atomic force microscopy. The appearance of plasmonic band gap was measured by spectral-angular polarisation spectroscopy. We experimentally determined the dependance of plasmonic band gap properties (width and position) on geometrical parameters of biperiodic plasmonic crystals. We also performed FDTD numerical simulations (Lumerical). The experimental results are in good agreement with numerical calculations. [1] Raether, Heinz. [Surface Plasmons on Smooth and Rough Surfaces and on Gratings.], Springer Berlin Heidelberg, 91-105 (1988). [2] Barnes, William L., et al. "Physical origin of photonic energy gaps in the propagation of surface plasmons on gratings." Physical Review B 54.9 (1996): 6227. [3] Kocabas, Askin, S. Seckin Senlik, and Atilla Aydinli. "Plasmonic band gap cavities on biharmonic gratings." Physical Review B 77.19 (2008): 195130.

Among the quantum systems capable of emitting single photons, the class of recently discovered defects in hexagonal boron nitride (hBN) is especially interesting, as these defects offer much desired characteristics such as narrow emission lines and photostability. Like for any new class of quantum emitters, the first challenges to solve are the understanding of their photophysics as well as to find ways to facilitate integration in photonics structures. Here, we will show our investigation of the optical transition in hBN with different methods: Employing excitation with a short laser pulse the emission properties in case of linear and non-linear excitation can be compared [1]. The possibility to perform two-photon excitation makes this single photon emitter an interesting candidate as a biosensor. We further show the behaviour of defects in hBN when being excited with different wavelengths and deduce the consequences for its level scheme. Here, it is found that the quantum efficiency of the emitters varies strongly with excitation wavelength, a strong indication of a branched level system with different decay pathways. [1] A W Schell et al., APL Photonics 1, 091302 (2016) [2] A W Schell et al., arXiv:1706.08303 (2017)

Metasurfaces provide great feasibilities for tailoring both propagation waves and surface plasmon polaritons (SPPs). Manipulation of SPPs with arbitrary complex field distribution is an important issue in integrated nanophotonics due to their capability of guiding waves with subwavelength footprint. Here, with metasurface composed of nano aperture arrays, a novel approach is proposed and experimentally demonstrated which can effectively manipulate complex amplitude of SPPs in the near-field regime. Positioning the azimuthal angles of nano aperture arrays and simultaneously tuning their geometric parameters, the phase and amplitude are controlled based on Pancharatnam-Berry phases and their individual transmission coefficients. For the verification of the proposed design, Airy plasmons and axisymmetric Airy beams are generated. The results of numerical simulations and near-field imaging are well consistent with each other. Besides, 2D dipole analysis is also applied for efficient simulations. This strategy of complex amplitude manipulation with metasurface can be used for potential applications in plasmonic beam shaping, integrated optoelectronic systems and surface wave holography.

A modified nanocone nanowire (NW) is proposed and analyzed for solar cell applications. The suggested NW consists of conical and truncated conical units. The geometrical parameters are studied by using 3D finite difference time domain (FDTD) method to achieve broadband absorption through the reported design and maximize its ultimate efficiency. The analyzed parameters are absorption spectra, ultimate efficiency and short circuit current density. The numerical results prove that the proposed structure is superior compared to cone, truncated cone and cylindrical nanowires (NWs). The reported design achieves an ultimate efficiency of 44.21% with an enhancement of 40.66% relative to the conventional conical NWs. Further, short circuit current density of 36.17 mA/cm² is achieved by the suggested NW. The modified nanocone has advantages of broadband absorption enhancement, low cost and fabrication feasibility.

The magnetooptical control of light implies different directions of polarization plane rotation, linear-to-circular and other polarization transformations. These opportunities can be opened using polarization-sensitive resonances, for example, Bloch surface waves (BSWs) and waveguide modes (WGMs) in magnetophotonic crystals (MPCs) [1]. Magneto-optical phenomena, such as Faraday effect, can be significantly increased near spectrally narrow optical resonances [2]. In this case, the Faraday rotation angle is determined both by the magnetic properties of the material and by the Q-factor of the resonances, which define their spectral width. The resonance of the BSW is shown to be extremely narrow. The proper choice of the MPC parameters gives the ways to observe the s-polarized BSW and p-polarized WGM of the MPC in the same spectral region. Here, we experimentally demonstrate how a fundamental property of magneto-optical effects to couple two linearly polarized modes allows one to control and modify the values of Faraday rotation angles. The interplay of the BSW and WGM results in an enhancement of the Faraday rotation angle, change of lineshape of Faraday rotation spectra and direction of the polarization rotation. Reflectance spectra of the one-dimensional magnetophotonic crystal and the corresponding Faraday rotation spectra were experimentally measured using the Kretschmann attenuated total internal reflection configuration and numerically calculated using the transfer matrix approach [3]. The studied magnetophotonic crystal sample consists of 15 alternating layers of fused quartz and Bi-substituted yttrium-iron-garnet on a sGGG substrate. The BSW excitation corresponds to a narrow resonance in the reflectance spectra of the s-polarized light. Wide dips in the reflectance spectra of p-polarized light correspond to the WGM resonances. As the incident angle increases, both the resonances shift to short wavelengths, but the WGM resonance shifts faster; thus, the spectral distance between the BSW and WGM resonances decreases. The spectral dependence of the Faraday rotation angle of s-polarized light has a feature coinciding in the BSW wavelength and caused by the BSW excitation. The feature in the Faraday rotation spectrum has a Fano resonance shape and changes from an asymmetric shape to a symmetric one, while the incident angle increases and the BSW and the WGM resonances approach each other. This behavior is observed both in the experiment and calculations. Thus, it can be argued that the spectral dependence of the Faraday rotation angle depends not only on the BSW resonance in the structure but also on the coupling of the BSW with the WGM mode that is not excited in the s-polarization of the incident light. Besides, the Faraday rotation changes direction while BSW and the WGM resonances spectral position approach each other that makes these resonance in MPCs promising for the future photonics devices. [1] M. N. Romodina, I. V. Soboleva, A. I. Musorin, Y. Nakamura, M. Inoue, A. A. [2] M. Inoue, M. Levy, A.V. Baryshev, Magnetophotonics: From Theory to Appli- cations, Springer Series in Materials Science, 2013. [3] D.W. Berreman, J. Opt. Soc. Am. 62, 502–510 (1972).

There is currently significant interest in operating devices in the quantum regime, where their behaviour cannot be explained through classical mechanics. Quantum states, including entangled states, are fragile and easily disturbed by excessive thermal noise. Here we address the question of whether it is possible to create non-reciprocal devices that encourage the flow of thermal noise towards or away from a particular quantum device in a network. Our work makes use of the cascaded systems formalism to answer this question in the affirmative, showing how a three-port device can be used as an effective thermal transistor, and illustrates how this formalism maps onto an experimentally-realisable optomechanical system. Our results pave the way to more resilient quantum devices and to the use of thermal noise as a resource.

Strong coupling between excitons and light leads to the formation of hybrid states with mixed properties of light and matter. As a result, interesting physical phenomena have been observed at room temperature, e.g. Bose–Einstein condensation and superfluidity, and novel applications are emerging, such as low threshold lasers and quantum devices. Recently it was shown that metasurfaces of aluminum nanoantennas coated with molecular J-aggregates can provide an excellent platform for the formation of strongly coupled exciton-localized surface plasmons (X-LSPs). However, their optical nonlinearities and temporal dynamics are still not well understood. In this work, we use femtosecond pump-probe spectroscopy to study X-LSPs in such composite Al/molecular metasurfaces on time scales that are longer than their Rabi oscillation period. We study the linear and nonlinear optical properties of the uncoupled and hybrid systems and find that the nanoscale plasmonic confinement in metallic nanoparticle cavities introduces intriguing new ultrafast phenomena in the strong coupling regime. These include modifications of the hybrid system due to femtosecond changes in the molecular environment, picosecond oscillations due to acoustic breathing modes of the nanoantennas, and long relaxation times of the nonlinear perturbation at the upper X-LSPs frequency band.

Geometric Spin Hall effect of light (SHEL) has attracted considerable attention because of the universality of this variant of the spin Hall shift and its independence on the light-matter interactions and materials properties. However, the magnitude of geometric SHEL is typically very small, in the sub-wavelength domain, making it difficult for direct experimental observation. Here, we have applied weak measurement schemes to amplify and faithfully observe the geometric SHEL. In our experiment, the input beam is pre-selected in linear polarization basis (p- or slinear polarization) and post selections are done at nearly orthogonal linear polarizations (small angle ϵ away from the exact orthogonal).This results in weak value amplification (~cotϵ) of the resulting shift of the beam centroid. Moreover, this process also leads to selective conversion of spatial to angular nature of geometric SHEL, which along with the weak value amplification leads to manifold amplification of the resulting SHEL, enabling its reliable experimental detection. A key feature of our weak measurement scheme is that both the weak perturbation (tiny geometric SHEL) and the post selection are done simultaneously by a single optical element, namely, a linear polarizer. The dependence of the weak value of the geometric SHEL on the pre and the post selection of polarization states in both linear and elliptical basis were also investigated in details. The specifics of the different weak measurement schemes, various intriguing experimental manifestations of the weak value amplified geometric SHEL, their analysis / interpretation via polarization operator based treatment of weak measurements is presented here.

The short wavelength of graphene plasmons relative to the light wavelength makes them attractive for applications in optoelectronics and sensing. However, this property limits their coupling to external light and our ability to create and detect them. More efficient ways of generating plasmons are therefore desirable. Here we demonstrate through realistic theoretical simulations that graphene plasmons can be efficiently excited via electron tunneling in a sandwich structure formed by two graphene monolayers separated by a few atomic layers of hBN. We predict plasmon generation rates of ~ 10^12 - 10^14 1/s over an area of the squared plasmon wavelength for realistic values of the spacing and bias voltage, while the yield (plasmons per tunneled electron) has unity order [1]. Our results support electrical excitation of graphene plasmons in tunneling devices as a viable mechanism for the development of optics-free ultrathin plasmonic devices. [1] S. de Vega and F. J. García de Abajo, ACS. Phot. 4 (2017)

The combination of nonlinear and integrated photonics enables applications in telecommunication, metrology, spectroscopy, and quantum information science. Pioneer works in silicon-on-insulator (SOI) has shown huge potentials of integrated nonlinear photonics. However, silicon suffers two-photon absorption (TPA) in the telecom wavelengths around 1550 nm, which hampers its practical applications. To get a superior nonlinear performance, an ideal integrated waveguide platform should combine a high material nonlinearity, low material absorption (linear and nonlinear), a strong light confinement, and a mature fabrication technology. Aluminum gallium arsenide (AlGaAs) was identified as a promising candidate for nonlinear applications since 1994. It offers a large transparency window, a high refractive index (n≈3.3), a nonlinear index (n2) on the order of 10^-17 m2W⁻¹, and the ability to engineer the material bandgap to mitigate TPA. In spite of the high intrinsic nonlinearity, conventional deep-etched AlGaAs waveguides exhibit low effective nonlinearity due to the vertical low-index contrast. To take full advantage of the high intrinsic linear and nonlinear index of AlGaAs material, we reconstructed the conventional AlGaAs waveguide into a high index contrast layout that has been realized in the AlGaAs-on-insulator (AlGaAsOI) platform. We have demonstrated low loss waveguides with an ultra-high nonlinear coefficient and high Q microresonators in such a platform. Owing to the high confinement waveguide layout and state-of-the-art nanolithography techniques, the dispersion properties of the AlGaAsOI waveguide can be tailored efficiently and accurately by altering the waveguide shape or dimension, which enables various applications in signal processing and generation, which will be reviewed in this paper.

Photonic devices performing required temporal and spatial transformations of optical signals are of great interest for a wide range of applications including all-optical information processing and analog optical computing. Among the most important operations of analog optical processing are the operations of temporal and spatial differentiation. Various types of resonant photonic structures performing these operations were previously proposed, such as phase-shifted Bragg gratings and other multilayer structures, resonant diffraction gratings, and nanoresonators. In the current work, we present an overview of our recent results dedicated to the design of resonant nanophotonic structures for optical implementation of various differential operators including integrated structures for Bloch surface waves and guided modes. A special attention is paid to a simple planar (integrated) optical differentiator consisting of two identical grooves on the surface of a dielectric slab waveguide (the details are presented in our recently published work [L. L. Doskolovich, E. A. Bezus, N. V. Golovastikov, D. A. Bykov, and Victor A. Soifer, “Planar two-groove optical differentiator in a slab waveguide,” Opt. Express 25(19), 22328–22340 (2017)]). The studied planar differentiator operates in reflection and enables temporal and spatial differentiation of optical pulses and beams propagating in the waveguide. The differentiation is associated with the excitation of an eigenmode localized at the ridge cavity located between the grooves. We show that by changing the groove length one can choose the required quality factor of the resonance (and, consequently, the linearity interval of the transfer function of the differentiator) in accordance with the width of the frequency or spatial (angular) spectrum of the incident pulse or beam. The presented numerical simulation results demonstrate high-quality spatial, temporal and the so-called spatiotemporal differentiation. The proposed differentiator may find application in the design of on-chip all-optical analog computing and signal processing systems.

In our work, we employ the resonant electromagnetic properties of III-V semiconductor nanowires to design building blocks for nonlinear all-dielectric metamaterials and devices. Contrary to widely used Si and Ge nanostructures, III-V materials, such as GaAs or AlGaAs, have a direct band gap and non-centrosymmetric crystal structure, which makes them promising for the development of nonlinear metamaterials. We developed an innovative approach to fabricate disk and rod nanoantennas by slicing bottom-up grown nanowires using a focused ion beam milling (FIB). The proposed method allows to significantly decrease the influence of the substrate on the electromagnetic field distribution inside the nanoantenna and it opens the possibility to use any substrate regardless of the nanostructure fabrication process. With this technique, we study the influence of geometry, design and crystal structure on the characteristics of all-dielectric nanoantennas. It offers unique opportunities to fabricate high-quality structures with variable radii, longitudinal heterostructures with lattice-mismatched materials, and structures with different refractive indexes and crystal phases that are not available in bulk materials.

Single-nanoantenna has intrigued vast interest due to its exceptional properties such as light harvesting and field enhancement, which provide the opportunities for strengthening light-matter interaction and efficient photon manipulation in nano-scale, as well as boosting nonlinear response. On the other hand, materials with structural or electronic phase transition have been employed to achieve large optical modulation contrast and order-unity switching, making them promising building blocks for high-performance optical circuits and devices with ultra-small footprint. In this context we demonstrate nano-scale all-optical modulation with single Au antennas fabricated on phase-transition material vanadium dioxide (VO2) substrate. VO2 films are deposited on boroaluminosilicate glass coated with a 30-nm layer of fluorine-doped tin oxide. The inclusion of this intermediate layer allows the production of VO2 films with low surface roughness and suitable thermochromic transition temperature. Then the nanoantennas are fabricated by e-beam lithography and subsequent 45-nm-thick gold deposition on the VO2 substrate. A 5-nm-thick Ti layer is used to improve the adhesion of the gold to the VO2. We use a pump-probe spectroscopy to characterize the modulation feature of the antenna/VO2. The pump beam at 1060 nm wavelength is used to introduce a local heating for VO2's phase transition and the probe beam from 1100 nm to 2000 nm wavelength is for readout of the modulated local transmission of antenna/VO2 hybrid owing to the dielectric environment change. A spatial modulation technique is also used to extract the differential transmission (ΔT/T) around the antennas. As a result, with pump pulse energy increasing to less than 1 nJ, the measured ΔT/T of single-antenna//VO2 hybrid exhibits substantial change that crossing the zero line and significant blue shift. As reported the ΔT/T obtained from spatial modulation spectroscopy is supposed to be proportional to the antenna’s extinction cross section. However, with the obtained negative values which lead to unphysical extinction cross sections less than 0, we believe the VO2 substrate beneath the antennas is highly involved as its optical property has been modified considerately. In addition, we observe that the pump-modulated differential transmission of the antenna/VO2 hybrid evidently depends on the polarisation of the pump when it is below a certain level. In this regime, the parallel pumping excites the longitudinal resonant mode while the perpendicular one only induces non-resonant absorption of antenna’s transverse mode. Going beyond this regime, the stronger pump transits the VO2 substrate from insulating phase into metallic phase completely, which dominates the dielectric environment change of the antenna, leading to nearly polarisation-independent modulation. The time for fully switch-on obtained from the pump-probe measurement is less than 50 ps. We also investigate the time response of the differential transmission dependent on the pulse repetition rate and substrate temperature, respectively. Less modulation depth with repetition rate over 2 MHz or base temperature higher than 40 °C suggest that the heat accumulation from adjacent pulses and thermal equilibrium time plays important roles in the achievable modulation speed. The single-antenna/VO2 structure may find applications in nano-scale optoelectronics for multiple functionalities including modulation, memory and so on.

The search for the new nanoscale functional materials has led to the emergence of the quantum dots (QDs) nanoengineering as a leading field of contemporary science. In recent years, special scientific attention has been devoted to the novel group of ternary I-III-VI QDs from which the chalcopyrite-type AgInS2 (AIS) have become one of the most interesting and important material for further applications, due to its reduced toxicity, red-shifted absorption and emission and high tolerance to off-stoichiometry. Despite their good luminescence properties, there is a need for extensive research to comprehend the physical nature of the electronic transitions in AgInS2 quantum dots. Because of the defect related nature of those structures the donor-acceptor pair (DAP) model is mostly indicated as the origin of emission in AIS QDs. However, limited applicability of the DAP model to highly confined structures indicate different physical mechanisms of luminescence which are still under discussion. The specific problem connected with the AIS QDs is their defect mediated kinetics of excited states relaxation resulting in highly non-exponential luminescence decays, effective trapping of the fundamental excitations and effective non-radiative relaxations [1]. Recent experiments [2,3] show that the incorporation of the pool of non-bonding electrons near the quantum dot can influence the mechanisms of excited state relaxation and significantly reduce dark states resulting in the enhancement of the QDs luminescence. Previously it was realized as the metallic gold shell around the quantum dot [2] or by placing the QDs on the metallic nanoparticles thin film [3]. Due to the known high tolerance of the AgInS2 chalcopyrite structure to off stoichiometry the excess of non-bonding electrons can be accomplished by the synthesis of non-stoichiometric metal-rich AIS QDs. Density functional theory calculations show, that the excessive Ag atoms in Ag-In-S nanoclusters result in the formation of the additional electronic energy levels near the HOMO (highest occupied molecular orbital) level with molecular orbitals of clearly non-bonding characters. In this paper we show the improvement of the luminescent properties of AIS QDs due to the deviation from stoichiometry. The results of the synthesis and optical measurements for the series of Ag(1+x)InS2 (x = -0.2, -0.1, 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) QDs samples are presented. The red-shift and widening of the luminescence spectrum have been observed with the increasing of the metal amount. Femtosecond time-resolved fluorescence spectroscopy measurements reveal minor deviation from the exponential decay for the Ag-rich AIS QDs in comparison to the stoichiometric ones. It was concluded, that such behavior was inducted by the excess of non-bonding electrons in metal-rich structures. [1] Cichy B et al. Two blinking mechanisms in highly confined AgInS2 and AgInS2/ZnS quantum dots evaluated by single particle spectroscopy. Nanoscale 2016;8:4151–9. [2] Ji B et al. Non-blinking quantum dot with a plasmonic nanoshell resonator. Nat Nanotechnol 2015;10:170–5. [3] Ma X et al. Fluorescence enhancement, blinking suppression, and gray states of individual semiconductor nanocrystals close to gold nanoparticles. Nano Lett 2010;10:4166–74.

This paper focus on the theoretical investigation of quantum confined Stark effect (QCSE) in strain compensated SiGeSn/GeSn single quantum well (QW). Eigen energies in presence of electric field, for Г valley conduction band (Г- CB) and heavy hole band (HH)) are obtained from the self consistent solution of coupled Schrödinger and Poisson equations by finite difference method. Absorption coefficient considering excitonic effect for direct transition of HH band to Г valley is calculated. A significant shift in absorption peak towards longer wavelengths is observed.

Several coherent light sources with dimensions less than the diffraction limit were proposed and demonstrated in the last decade. One of the most popular of them is a spaser. Since its theoretical proposal, there were a number of experimental realizations based on metal nanoparticle colloids and laser dyes. However, the disaffection with these realizations grows as the conditions of the performed experiments were too close to that of the random-lasing phenomena. Hence, an experiment with a refined setup that greatly reduces an unintended feedback due to the multiple scattering events is in order. In this work, we achieved this goal by creating a monolayer of metal nanoparticles on the solid surface and cover them with a thin layer of dye molecules.

The identification of threshold in nanolasers still poses not entirely met challenges. Dynamical techniques offer interesting methods to determine the achievement of coherent emission. A recent experimental proposal rests on the dynamical shift of a bifurcation in the presence of a modulated pump indirectly observed through the study of the behaviour of the zero–delay second–order autocorrelation function of the detected photon number. This paper investigates the potential for directly observing the dynamical hysteresis which accompanies the sweep across threshold in a large β nanolaser. We conclude that the observation is possible in principle, but that the experiment has to be carefully designed to achieve this goal.

Multiply resonant silicon photonic devices based on three coupled nanobeam cavities are proposed engineer third order nonlinearities at wavelengths around λ=1.55μm. We show that varying the geometrical parameters allows a flexible tuning of linear properties of the system, especially the deviations between the cavity resonance wavelengths. Based on the linear regime results, the nonlinear properties of the system are studied using coupled mode expressions of the supermodes given by the Tight-Binding method for the calculation of the nonlinear integrals controlling the intensity of the third-order nonlinear effects of the photonic molecules. We geometrically control the self-phase modulation (SPM), the cross-phase modulation (XPM), and the degenerate four-wave mixing (DFWM) nonlinear coefficients of the three coupled nanobeam cavities and identify general trends for nonlinear applications such as optical switching and frequency conversion devices.

Being restricted to the domain of validity of spherical wave expansions, the T-matrix method has been in question to model light scattering by nonspherical particle systems when inter-particle distances are low. In this work, we discuss a formalism to account for multiple scattering between nonspherical particles in close vicinity. Accurate coupling between adjacent particles’ scattered fields is achieved by an alternative plane-wave formulation of the translation operator for spherical vector wave functions. The accuracy of the presented approach is demonstrated by a far field simulation of a large particle cluster. The near field of nonspherical particles has not been accessible in T-matrix simulations thus far. Utilizing the benefits of plane-wave expansions, the near field of nonspherical particles can be constructed in T-matrix simulations. We hereby show that the T-matrix method is also applicable for the analysis of localized resonances, making it suitable for the description of plasmonic systems.

The stochastic implementation of the laser rate equations is discussed in detail, in light of its application to numerically predict the properties of nanolasers. The deterministic integration scheme is analysed and tested for appropriateness to the problem. The simplest stochastic, first-order scheme is considered and its particular properties and requirements are discussed. Tests for the correctness of the numerical integration are presented. Finally, thorough tests for the convergence of the stochastic integration are performed, showing their different aspects and possible pitfalls.

In this paper, new design of Yagi-Uda nano-antenna (NA) based on ellipsoid shape is introduced and numerically analyzed using 3-D finite difference time domain method (3-D FDTD) via Lumerical software package. The NA parameters are optimized using the particle swarm optimization (PSO) algorithm to achieve high directivity at a wavelength of 500 nm for wireless point-to-point applications. To illustrate the performance of the proposed antenna, different radiation parameters such as radiation pattern, directivity, and radiation efficiency have been studied. The optimized ellipsoid nano-antenna shows a directivity of 22.36 which is enhanced by 86.3 % relative to the conventional spherical counterpart. Moreover, the fabrication tolerance of the reported design is studied to ensure the accuracy of the introduced NA parameters to the fabrications errors.

In order to detect DNA hybridization with label free and high sensitivity, a hybrid alternative plasmonic slot waveguide (HAPSW) biosensor based on silicon-on-insulator (SOI) is proposed and analyzed. The reported design increases the light interaction with the sensing region by using a slot-waveguide along with titanium nitride as an alternative plasmonic material. The suggested biosensor can detect the slightest change in the analyte refractive index with high sensitivity due to an ultra-high optical confinement in the low-index regions caused by the high index contrast and plasmonic enhancement. The effective index, normalized power confinement, and sensitivity are analyzed for the detection of the DNA hybridization. The simulation results are obtained using full vectorial finite element method (FVFEM). The suggested biosensor has high sensitivity of 1190 nm/RIU (refractive index unit) for DNA hybridization detection, which is very high relative to those reported in the literature to the best of our knowledge.

A novel design of multiplexer-demultiplexer (MUX-DEMUX) based on channel waveguide on silicon dioxide (SiO₂) is introduced and analyzed. The suggested structure consists of two neighboring channels infiltrated with nematic liquid crystal (NLC) material of type E7. The two channels are etched in the SiO₂ substrate. The electro-optic effect of the NLC is used to control the waveguide propagation condition using an external electric field. Additionally, a plasmonic wire is inserted between the two waveguides to enhance the suggested MUX-DEMUX in terms of compactness. The modal analysis of the y-polarized modes supported by the NLC MUX-DEMUX is carried out using full-vectorial finitedifference method (FVFDM). Further, the propagation characteristics through the reported design are obtained using full vectorial finite difference beam propagation method (FVFD-BPM). The design parameters of the NLC MUX-DEMUX have been studied to obtain an efficient waveguide coupling with a short device length. Moreover, the NLC MUXDEMUX has a compact device length of 1296 μm. The numerical results reveal that the reported MUX-DEMUX has a small insertion loss of 8x10^-6 dB with a good crosstalk better than -37 dB and -30 dB at the studied wavelengths of 1.3 μm and 1.55 μm, respectively. To the best of the authors’ knowledge, it is the first time to introduce a MUX-DEMUX based on channel on SiO² platform with a simple design and broadband operation.

We exhibit a structure built with inorganic and organic material nanostructure arrays. The zinc oxide (ZnO) nanorods were synthesized by hydrothermal method and could be the precursor model to build our nanostructure. The as-fabricated ZnO nanorods were then surrounded with the inorganic material, lead telluride (PbTe). It could be filled with the organic material, Poly Methyl Methacrylate (PMMA), in the hexagonal hole after the ZnO nanorods were removed by simple chemical aqueous etching process. Finally, we can obtain an organic/PbTe array matrix nanostructure.The thermoelectric properties of as-fabricated device were measured and temperature dependence of physical mechanism for organic and inorganic hybrid nanostructure was discussed.

Plasmonic quasicrystals stand out as the center of cynosure behind the many potential applications which emerges due to the quasi-periodic structure and metal dielectric patterns. The rotational symmetry elicits the optical properties resembling like crystals and and the metal dielectric nanostructure are being probed and explored in various disciplines of science and even in engineering also. Plasmonic quasicrystals composed of quasi- periodic and metal-dielectric patterns furnish efficacious benefits in improving the efficiency of solar cells, broadband transmission enhancement, and bio-sensing applications etc. Due to the intriguing properties of plasmonic crystals such as periodicity and short range ordering, the excitation of the surface Plasmon polaritons is restricted by a few fewer techniques such as polarization, launch angle dependence. Polarization contains wealth of information and holds the potential to control the interaction of light with metal Nano particles. Therefore, an exhaustive and thorough information regarding incident and scattered light is necessary for the examining the spectral response of the quasi crystal. Here, we report to the best of our knowledge the first ever quantitative polarimetric studies on the extremely complex plasmonic quasicrystal by recording a full 4x4 spectral Mueller matrix from the same and tried to explore the fascinating and interesting properties of quasi crystals. A homebuilt comprehensive Mueller Matrix platform (integrated with dark field microscope) is utilized to record the conventionally weak, intermixed polarization signal from plasmonic quasicrystals. These studies probed the enthralling phenomena of Fano resonance, explored and probed the presence of phase anisotropy in the plasmonic quasicrystals using the Mueller matrix derived retardance (δ) parameter. Additionally polarization mediated tuning of Fano Resonance is achieved too. Moreover it is demonstrated that the Mueller matrix derived diattenuation, retardance parameters probes the Fano resonance, phase and amplitude anisotropy from such complex plasmonic nanostructure and proved instrumental in polarization controlled tuning of Fano resonance.

In this study, the absorption capabilities of a plasmonic funnel-shaped silicon nanowire (SiNW) solar cell is introduced and analyzed by using 3D finite difference time domain method (FDTD). The reported NW design has titanium nitride (TiN) core as an alternative plasmonic material. The different geometrical parameters of the reported design are studied to maximize the absorption and hence the ultimate efficiency. An ultimate efficiency and short-circuit current density J_sc of 48.3% and 38.98 mA/cm², respectively are obtained which are greater than the conventional Si-Funnel counterpart by 46.36%. The enhancement of the light absorption is attributed to the combination between different types of optical modes and plasmonics modes of the funnel-shaped NW and the TiN, respectively.

In this paper by the methods of Raman spectroscopy, a drop of the evaporating liquid of Human Serum Albumin with the Rhodamine 6G dye molecules in the presence of silver nanoparticles obtained by laser femtosecond ablation in water was studied. In the Raman spectra, an increase in the intensity of scattering of dye molecules with silver nanoparticles the addition of protein molecules was recorded. We suppose that the observed effect is associated with the diffusion and thermal processes in the drop arising during laser excitation.

A hexagonal shape surface plasmon photonic crystal fiber (PCF) biosensor is reported and studied numerically. The proposed design has three identical cores along the y-axis filled with liquid (analyte). Additionally, the central core is coated by a gold layer to facilitate the coupling among the plasmonic modes and the core fundamental modes. A full vectorial finite element method is used to analyze the proposed sensor with a perfectly matched layer boundary condition. Further, the particle swarm optimization (PSO) technique is used to optimize and improve the sensitivity of the presented sensor as well as reduce the sensor’s size. Through the optimization process, the diameters of the three cores, and the thicknesses of the gold layer are fluctuated. For a wavelength range 1.46-1.47, the sensitivity of the proposed sensor is 4000 nm/RIU.

As performance and power consumption of modern micro-chips are increasingly limited by electrical on-chip interconnects, all-optical interconnect systems promise data transmission at speed of light and wavelength- division multiplexing. To realize complex networks, active devices, like lasers, need to be integrated on Si. III-Vs are excellent candidates for optical devices, however, their integration on Si is challenging due to a significant lattice and thermal mismatch. Template-assisted selective epitaxy (TASE) was recently developed by our group, allowing for the selective growth of III-Vs from a small Si seed in a confined oxide template. In this work, we extend TASE towards optical devices and demonstrate the monolithic integration of InGaAs lasers via a novel approach using a virtual substrate (VS) in a two-step templated growth. First, μm² sized 60 nm thick InGaAs VSs are grown by MOCVD using TASE on SOI. Subsequently, 500 nm oxide are deposited onto the VS and patterned in arbitrary shapes like disks, and rings. In a second InGaAs growth, the defined vertical cavities are filled. The investigated structures have diameters of 1.7 μm, thicknesses of 0.5 µm and total cavity volumes of 0.5 λ³₀. Photoluminescence spectroscopy reveals a broad spontaneous emission peak around 1.1 μm (FWHM = 150 nm) that increases linearly with pump power for low excitation powers (<< 2.6 pJ/pulse). Above excitation threshold, a strong emission peak emerges at 1.1 μm (FWHM = 7 nm). The Input-Output curve (log- log, T = 10 K) exhibits the characteristic S-shape which constitutes a strong indication for the lasing operation. The onset of the lasing threshold is observed up to 200 K with a characteristic temperature of T₀ = 192 K.

We show that scattering of plane waves leads to helicity-independent transverse spin angular momentum (SAM) and helicity-dependent transverse Poynting vector components. The in uence of plasmon resonance and avoided crossing for a sphere on these quantities is studied.

We demonstrate the realization of desired gold plasmonic nanostructures by direct laser writing (DLW) method employing a continuous-wave 532 nm laser. By moving the laser focusing spot of the DLW system, the gold nanoparticles (NPs) are formed following the laser moving path. The plasmonic patterns composing of gold NPs enable a lot of applications, such as direct text writing and inverse text writing at micro scale, bar code and QR code to store the messages, binary recordings as compared to standard CDs and DVDs. Furthermore, by controlling the laser intensity and/or the exposure time, the NPs size was changed resulting in different plasmonic colors, and offering a new method to nanoprint with color.

The optical processes of plasmonic enhancement of rhodamine 6G molecules fluorescence in dielectric films of polyvinyl alcohol deposited on a rough silver surface have been studied. The reflection coefficients of the polarized light components on rough silver surfaces have been determined by means of spectral ellipsometry and spectrophotometry methods. Two kinds of silver surfaces were used: without and with anodizing at current density of 5 mA/cm² of 0.5 μm layer. The plasmon spectrum appeared to be red-shifted after polyvinyl film deposition onto the silver plate. I was shown that the silver-dielectric interface roughness affects the position of the reflected light spectrum maximum to 360 – 400 nm range due to the dielectric polarizing effect.

The article explores the influence of plasma energy of ytterbium nanoparticles on the fluorescent and absorption characteristics of the porphyrin molecules (Ethioporphyrin) in methylcellulose films. There has been ascertained the presence of plasmon energy transfer in the porphyrin-cluster system of the ytterbium nanoparticle at the wavelengths of fluorescence registration. The values of the increase in percentage proportion were defined. It was demonstrated that with the clusters concentration increasing the optical density of porphyrin molecules and fluorescence intensity increases.

We investigate the optical properties of nanogap MIM nanoantennas with a 2.1 nm thick gap. These plasmonic nanoantennas consist of a gold film, an insulating layer deposited by Atomic Layer Deposition, and a periodically structured gold layer. MIM nanoantennas are characterized by a tunable spectral response and a high field confinement within the nanogap. Nanometric gaps enable high coupling between the plasmons of the top and bottom metal surfaces. We demonstrated an excellent agreement between optical measurements and classical electromagnetic simulations. In particular, we observed a fluctuation in the gap thickness of 0.2 nm.

A method for preparation silver nanoparticles supporting plasmon oscillations is proposed. Using a seed-mediated growth approach in a rod-like micellar media, silver nanorods of varied aspect ratio were prepared from nearly spherical silver nanoparticles. The concentrations of synthesis reagents were determined to obtain nanorods whose plasmon resonances are shifted toward larger wavelengths relative to resonances of spherical particles.

Coupling of a single photon source into photonic structures is highly demanded for implementation of numerous applications in quantum information processing and quantum dot (QD)-based solid-state platforms. In this work, we present a simple strategy for coupling a single semiconductor colloidal nanocrystal (NC) into polymer-based photonic structures. By utilizing low one-photon absorption (LOPA) direct laser writing (DLW) technique, we demonstrate the precise patterning of 2D SU-8 microstructures containing an individual core/shell CdSe/CdS NC. Various shapes of desired structures are fabricated with a single embedded NC while keeping its photon antibunching property as a single photon source. These results open a wide range of perspectives in term of quantum information, tunable emission, and efficient light harvesting by using polymer-based photonic crystal.

We studied the influence of the ligands on the optical properties of PbS QD solids using the photoluminescence spectra and the kinetics of photoluminescence decay. As the ligand molecule length decreases, the photoluminescence decay becomes faster, which in a good agreement with the theory of the hopping mechanism of charge transfer in QD solids. We also fabricate photovoltaic structures (ITO/PEDOT:PSS/PbS/ZnO/Al) based on PbS QD solids and investigate the influence of various organic ligand molecules on its photovoltaic characteristics. The maximum efficiency was observed in samples with a ligand of intermediate length.

Using an optical pump and a time delayed white light super continuum probe, delay dependent switching is achieved between saturation absorption (SA) and reverse saturation absorption (RSA) above a threshold pump intensity in reduced graphene oxide (RGO2). RGO2 is obtained using photo-thermal reduction and chemical reduction respectively. The wavelength regime which experience switching can be varied by changing the degree of reduction. At 415 nm pump, the threshold intensity to obtain switching property decreases to 9 GW/cm² for RGO2 from 18 GW/cm² in graphene oxide(GO) and the tunability range shifts from 471-526 nm for as grown GO to 519-623 nm in maximally reduced RGO2.Though the saturation intensity of intrinsic non-degenerate two photon absorption (nd-TPA) is found to be lower in GO (4.3 GW/cm²) than RGO2 (18.2 GW/cm²), nd-TPA coefficient increases from 0.0015 cm/GW (GO) to 0.0026 cm/GW (RGO2) with increasing reduction. Decay dynamics of scattering processes show faster relaxation of electron in RGO than in GO. Results are accounted using a model band diagram based on amorphous-carbon model.

We propose a horizontally symmetrical three-layer dielectric structure composed of a high-index central (core) layer surrounded by two identical low-index cladding layers, which acts as an optical differentiator in reflection. If the refractive index of the surrounding medium is greater that the refractive index of the cladding layers, the spectra of the considered structure may exhibit resonant features associated with the excitation of a leaky mode localized at the central layer. At resonant conditions, the reflection coefficient will vanish at certain values of frequency and angle of incidence, which enables the differentiation of the incident optical pulse. We theoretically justify that this three-layer structure can perform temporal differentiation (differentiation of an incident optical pulse envelope), spatial differentiation (differentiation of an optical beam profile) and the so-called “spatiotemporal differentiation” (differentiation of an optical signal envelope along a certain direction in the (x,t)-plane). Rigorous numerical simulation results demonstrate high quality of differentiation. It is shown that the resonance quality factor increases with the increase in the thickness of the cladding layers, which makes it possible to achieve a required linearity interval of the differentiating filter. The proposed differentiator is more compact than Fourier correlators containing graded-index lenses and substantially easier to fabricate than metasurface-based devices incorporating periodically arranged nanoresonators and may find application in ultrafast analogue computing and signal processing systems.

Here, we present the design and fabrication details of a metal grating-one dimensional photonic crystal (1DPhC) structure that can efficiently couple the normal incident light into the 1DPhCs. We implement this by designing a silver (Ag) nano-grating on the 1DPhC which consists of 10 bilayers of SiO2/TiO2 thin films on a silicon substrate. Ag coated 1DPhC shows a sharp dip in the reflectivity within the photonic stop band, which is a distinct signature of the excitation of Tamm states at the interface of metal-1DPhC boundary. Reflection spectrum of Ag grating–1DPhC structure shows that the Tamm state is modified in the presence of the Ag grating, giving rise to a surface state in the vicinity of the Tamm resonance. The experimental results obtained are well supported by simulations which provide the field distributions for the Tamm resonance and the surface state.

Fluorescent nanomaterials such as metal nanoclusters (NCs) have become one of the most essential nanomaterial and attracted abundant attention in research due to their excellent photophysical properties and wide range of applications. Furthermore, metal nanoclusters have been predominantly investigated owing to its excellent optical properties, simple synthetic routes,low toxicity and excellent photostability. However, limited advancements and progress have been executed in fabricating hydrophilic and highly luminescent metal NCs. Copper is an eco-friendly, low-cost metal which is progressively advancing into focus for metal NCs research. In comparison to the extensively studied gold nanoclusters (Au NCs) and silver nanoclusters (Ag NCs), systematic and analytical applications of the copper nanoclusters (Cu NCs) are relatively limited and still at an early stage. In this review, we fixate on contemporary advances in the analytical applications of Cu NCs based on their behavior and properties of light. This work specifically addresses optical properties and some emerging applications of Cu NCs. The study seeks to unravel some unique photophysical properties of Cu NCs in its solid state, namely concentration/aggregation induced emission enhancement, thermally activated delayed fluorescence (TADF), by which both singlet and triplet excitons can be harvested. Furthermore, the as-synthesized Cu NCs used in this study was remarkably excellent, garnering ~20% quantum yield in colloidal and solid-state form, respectively. CuNC/PVA nano-composites can exhibit unique solidstate- induced dual-mode emissions of thermally activated delayed fluorescence (TADF) and phosphorescence at ambient environment. The outstanding performance of Cu NCs in solid-state makes it an excellent biocompatible nanoemitters light-emitting devices.

Plasmonic nanocircuits have the potential to open up new routes in manipulating optical information beyond the diffraction limit and future quantum information processing technologies. We present on-chip polarization conversion based on interaction between two interfering surface plasmon modes supported by metal-insulator-metal (MIM) waveguides. The functional device is realized by all-plasmonic Mach-Zehnder Interferometers (MZI) equipped with impedance-matched Yagi-Uda style nanoantennas for highly efficient far-field coupling. By controlling the relative phase difference between guided MIM gap plasmons propagating in a MZI, namely by precisely differentiating the individual path length, a rotation of the mode optical axes is observed. Depending on the phase difference the resulting mode at the junction point, where two branching channels merge into one channel, can be symmetric or antisymmetric. Accordingly, two cases are investigated in ultra-compact (< 40 μm²) high-definition circuits, where the antisymmetric and symmetric mode are distinguished by observing the origin position and the polarization of the scattering signals. A high conversion efficiency can be realized, encouraging potential application in functional plasmonic nanocircuits.

The optical properties of organometallic films of silver nanoparticles and J-aggregates of pseudoisocyanine dye have been studied to observation of the plasmon-exciton interaction. The original method for obtaining J-aggregates on inhomogeneous island silver films without use of salt and water was developed. Owing to the broad bandwidth of inhomogeneous plasmon resonances; it is possible to study the interaction of nanoparticles and J-aggregates, obtained in the spin-coated layer on the silver island film. The absorption spectrum of the organometallic film is not a simple sum of the spectra composing its components. The absorption of dye molecules increases several times in the presence of silver nanoparticles, which is due to the influence of the near fields of the latter. The spectral dip in the absorption maximum of the J-aggregate of pseudoisocyanine was observed; it became more symmetrical with an increasing equivalent thickness of the island film.

In this study, we have investigated the potential of bimetallic hollow nanostructures (BHNS) consisting of silver and gold metals for the detection of mercury in an aqueous medium. The BHNS of varying compositions of gold and silver were prepared by galvanic etching of the template silver nanoparticles (AgNPs) using gold(III) salt solution. The BHNS of varying composition were prepared by modulating the molar ratio, of gold to silver, ranging from 0.13 to 2.0, in the reaction mixture. The resultant nanostructures were characterized using UV-Vis spectroscopy and transmission electron microscopy. The absorption maxima of the BHNS batches were found to be increased from 463 ± 9 nm to 611 ± 12 nm as a function of gold to silver molar ratio. An increase in the nanoparticles size was observed from 54 ± 6 (molar ratio = 0.25) to 75 ± 10 (molar ratio = 2.0) with an increase in gold to silver molar ratio. The interaction of different volumes of mercury solution (ranging from 0.1 to 0.4 mL) with all types of BHNS was studied. A considerable change in color of the solution was observed and consequently, a change in the absorbance intensity and a shift in the peak plasmonic wavelength was also noticed. Among the different BHNS batches investigated, the highest change in the intensity and peak wavelength was observed for BHNS0.13, with higher silver and lower gold content. This suggests that the reaction between silver and mercury is more favored compared to that between mercury and gold.

CZTS (Cu2ZnSnS4) based solar cell has many advantages as its materials are earth abundant and low cost. However, its efficiency is low compared with other thin film solar cells. Enhancing efficiency of CZTS solar cell could be achieved using nanostructures for controlling light propagation using nanophotonics techniques. Recently, metamaterial has been used widely for guiding and confining electromagnetic waves over entire wave- length range. Cross grating metasurface would be possible for reducing light reflection and increasing generated photocurrent inside CZTS solar cells. Herein, we studied theoretically effect of using different plasmonic cross grating metasurface above or below CZTS active layer. Then, we replaced plasmonic material with all dielectric metasurface to compare how light losses inside metasurface would reduce and light coupled to CZTS active layer increase. Moreover, we studied how using dielectric coating for metasurface would increase or decrease active layer light absorption. Our findings indicate that, light absorption enhancement in CZTS active layer is largely depend on material, coated material, dimension and pitch of proposed cross grating wires. Our results suggest certain nanostructure to be used for getting better photocurrent and efficiency. All proposed nanostructures done in this study made in three-dimensional using finite element method simulation tool, and use measured solar spectrum as input power. Using proposed cross grating metasurface with suggested material coating, would enhance overall efficiency of CZTS solar cells.

Solutions of nanofluids composed of dispersed metal-nanoparticles in water, possess exceptional thermo-optical properties. In the present work was studied the variation in the thermo-optical properties of nanofluids composed of metal-nanoparticles with different surfactants. It was used the single-pulsed laser excitation dual-beam mode- mismatched termal lens spectroscopy (TLS) for liquid samples. An experimental set-up of TLS was used and the thermal diffusibility and the dn/dT value of different nanofluids were studied, for this an Ar+ laser (514nm and 15.4mW) was used as excitation beam and a He-Ne laser (635nm) as a probe beam. The experiment showed that the thermal diffusibility of nanofluids is affected by the nature of the stabilizer, also it was observed an increase in the thermal diffusibility of nanofluids with respect at water without nanoparticles, for nanofluids with functionalized nanoparticles with PEG and SDS the heat transfer decreases compared to nanofluids without stabilizers.

The CdSe-based quantum dots (QDs) have been applied to light-conversion nano-phosphors due to tunable emission and pure colors. However, these cadmium-containing QDs was strongly toxic and synthesized in a hazardous solvent. In addition, conventional QD nano-phosphors with a small Stokes shift suffered from reabsorption losses and aggregation-induced photoluminescence (PL) quenching in the solid state. Therefore, there is a need to develop nanophosphors with a large Stokes shift. Here, we demonstrate one-pot synthesis of gold nanoclusters (AuNCs) using 3- aminopropyltrimethoxysilane (APS) and glutathione as protection ligand with a large Stokes shift. The gold nanoclusters with a large Stokes shift can mitigate the aggregation-induced PL quenching and reabsorption losses, which would be potential candidates for "green" nano-phosphors.

Heavy-metal-containing quantum dots (QDs), such as CdSe-based quantum dots (QDs) have been applied to lightconversion nano-phosphors due to tunable emission and pure colors. Unfortunately, those QDs involve toxic elements and synthesize in a hazardous halogenated solvent. Therefore, Eco-friendly gold nano-clusters (AuNCs@GSH) in solution phase have gained much attention for promising applications in biophotonics. For the first time, we explore the feasibility of aqueous-solution-processed AuNCs@GSH as luminescent species for promising applications in "green" luminescent solar concentrators (LSCs) by investigating their photophysical properties. Due to ligand-to-metal chargetransfer (LMCT) state, we found that such "green" LSCs formed by Zn-AuNCs@GSH dispersed in a polymer matrix exhibit large Stokes shift and small scattering losses. Compared to AuNCs@GSH, the Zn-AuNCs@GSH dispersed in a polymer matrix could suppress non-radiative recombination rates, inducing the enhancement of luminescence and the increase of PL-QY from 2% to 40%.

In this research, we have synthesized graphene quantum dots (GQDs) concurrent with N doping by pulsed laser ablation (PLA) of graphene oxide (GO) with urea. The synthesized N-doped GQDs (N-GQDs) with an average diameter less than 5 nm and N/C atomic ratio of 33.4% have been demonstrated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The temperature dependence of the photoluminescence (PL) intensity in GQDs and N-GQDs were investigated. The PL intensity of the GQDs was quenched monotonously with increasing temperature. However, an unusual enhancement of PL intensity in N-GQDs was observed with temperatures within the temperature range of around 50-150 K. We suggest that the distinct dependence of PL intensity of N-GQDs on the temperature originated from a carrier transfer mechanism between the N-dopant induced state (energy level) and quantum-dot emitting states. This study is rendered advantageous in understanding the effect of N-doping on the luminescence properties of GQDs useful for the potential applications.

Periodic arrays of nanoparticles whose period is commensurate with the wavelength of light can sustain collective resonances known as surface lattice resonances (SLR). SLR are associated with sharp and intense resonances and are appealing for fluorescence enhancement. In this communication, we design an array of double bowtie antennas for fluorescence enhancement of any large Stokes-shift emitter. A single emitter is located in the center of the central antenna. Each antenna is composed of two perpendicular bowties: an aluminum bowtie along the X-axis designed to enhance the excitation rate of the emitter and a gold bowtie along the Y-axis design to enhance the emission rate. Our goal is to enhance simultaneously excitation, emission and directivity within a single design. First, we study the properties of a single double bowtie (”nanoclover”) antenna for fluorescence enhancement. Then, we discuss the properties of one-dimensional arrays (chains) of nanoclovers. We evidence a subradiant mode sustained by the chain, leading to an increased absorption and detrimental to fluorescence enhancement. A strategy to circumvent this issue is proposed.

A fundamental problem in the integration of photonic elements is the problem of the light localization and the creation of nanolocalized laser sources of radiation. A new approach in the miniaturization of lasers is the approach based on using plasmon fields instead of photon fields. Plasmons arise from the interaction of the oscillations of the electron density and the electromagnetic fields that excite them. Accordingly, the electromagnetic effects caused by these fields occur in the subwavelength region near the surfaces, namely, in the nanometer range. Therefore, the approach allows to overcome the diffraction limitation on the laser size. Plasmonic nanolaser is a nanoscale (at least in one dimension) quantum generator of nanolocalized coherent plasmon fields. The nanoscopic in all three dimensions plasmon nanolaser has a different name: SPASER (Surface Plasmon Amplification by Stimulated Emission of Radiation). It is based on patterned metal film. The precision of formed structures and the dielectric properties of the metal are critical factors in determining any plasmonic device performance. Surface and morphology inhomogeneities should be minimized to avoid SPP scattering during propagation and etching anisotropy. Moreover, the metal should have high conductivity and low optical absorption to enhance optical properties and reduce losses. Some researchers focused on developing new low-loss materials (nitrides, highly-doped semiconductors, semiconductors oxides, or two-dimensional materials), but silver and gold are the most commonly used materials in optics and plasmonics due the lowest optical losses in visible and near infrared wavelength range. Recently, we have presented plasmonic nanolaser built on ultra-smooth silver films. Nanoscale structure in metallic films are typically fabricated by a two-step process. Metals are first deposited using evaporation or sputtering on a substrate and then patterned with focused-ion-beam milling or e-beam lithography and dry etching. If the deposited films are polycrystalline, etch rates vary for different grain orientations and grain boundaries. Therefore, the patterned structures could differ from each other. One of the possible solutions is to deposit singlecrystalline metals, which will be etched more uniformly and lead to precise structures. Another approach deals with large grain (<300 nm) polycrystalline film preparation. The fabricated silver films showed ultra-low losses (40 cm−1). Built on it a plasmonic laser demonstrated the lasing at 628 nm with a linewidth of 1.7 nm and a directivity of 1.3.

We explore photonic crystals based on a triangular lattice of rods. Non-circular rods break the inversion symmetry of the lattice and removes degenerate modes at the K-point (Dirac point) that are protected by symmetry from the band structure. A sizable complete photonic band gap of 7.5% relative gap width ▵w/w can be created by maximal symmetry breaking. We achieve this maximal symmetry breaking by rotating equilateral triangles over 30° relative to the lattice directions. The gap width depends on the rotation angle and a near perfect sinusoidal dependence is found, hinting at a simple mechanism for gap formalism. The gap can be further maximized by tuning the size of the triangles and we report a photonic bandgap map for a structure with inversion symmetry and with maximally broken inversion symmetry. Once a gap is formed interesting edge modes can be created by joining two crystals rotated by 180°. This restores inversion symmetry at the edge and creates line defect modes that are different for the different edges. These defect modes offer interesting possibilities for future nanophotonic devices where the on-chip functionality and localization of light is protected by the symmetry of the edges.

Here we report theoretical and experimental results for a high-Q cavity based on nanoimprinted perovskite film. We reveal that bound state in the continuum transformed into a resonant state due to leakage into substrate leads to significant enhancement of the photoluminescence signal of the perovskite cavity.

The spectroellipsometer based on DMR-4 spectrometer was automated. An electronic system and software for the automation of equipment was designed and built. The system was calibrated and for the purpose of verification of optical constants of metals samples such as gold, silver and copper were measured. The device automatically measures metal surfaces by Beattie-Conn method. It was measured values of optical constants of metal and compared them with table data. Graphs were built by experimental and table data, they demonstrate the results of measurements of metal samples coincided with theoretical data. Optical constants of surface based on heterostructures Cr_1,5nmAu_47nmHfO_{2_7nm} were measured by Beattie-Conn method too.

The generation of slow surface plasmon polaritons in a single-walled carbon nanotube is investigated theoretically. A mechanism of amplification of surface plasmon polaritons is based on the direct transfer of electromagnetic energy from a drift current in the nanotube into a surface wave.

The article is devoted to the spectral analysis of volume holograms recorded in materials with diffusion-based formation mechanisms. Two media of different nature were examined: polymer material with photosensitive macromolecules (PQ-PMMA) and additively colored solid-state crystal (CaF₂). Differential spectra of holograms optical parameters were determined by means of two approaches: numerical approximation of both spectral and angular hologram response (selectivity hypercontour) by Coupled wave theory and processing hologram spectra by Kramers-Kronig dispersion relations. The operation principles, experimental performance, determination results, advantages and disadvantages, as well as validity limits were discussed for both the approaches. Kramers- Kronig relations are operable tool in cases where the nature of holograms formation is well studied, whereas hypercontour approach is indispensable for investigation of hologram formation mechanisms.