How close are Integrable and Non-integrable Models: A Parametric Case Study Based on the Salerno Model

n the present work we revisit the Salerno model as a prototypical system that interpolates between a well-known integrable system (the Ablowitz-Ladik lattice) and an experimentally tractable non-integrable one (the discrete nonlinear Schrödinger model). The question we ask is: for generic initial data, how close are the integrable to the non-integrable models? Our more precise formulation of this question is: how well is the constancy of formerly conserved quantities preserved in the non-integrable case? Upon examining this, we find that even slight deviations from integrability can be sensitively felt by measuring these formerly conserved quantities in the case of the Salerno model. However, given that the knowledge of these quantities requires a deep physical and mathematical analysis of the system, we seek a more generic diagnostic towards a manifestation of integrability breaking. We argue, based on our Salerno model computations, that the full spectrum of Lyapunov exponents could be a sensitive diagnostic to that effect

Enhanced natural sunlight- and artificial UV-driven photocatalytic activity of mechanically activated ZnO/SnO2 composite

Over the past four decades there is an increasing interest to develop highly efficient semiconductor photocatalysts for degradation of organic and biological pollutants in water under light irradiation. The semiconductor band gap determines which wavelength of light will be absorbed; precisely, semiconductors with a wide band gap (> 3 eV) can absorb only UV light, while those with a narrow band gap (< 3 eV) can be activated by visible light. In this study we examined structural, morphological, textural and optical properties of ZnO/SnO2 composite as potential photocatalyst. Mechanical activation of commercial ZnO and SnO2 powders has been used to produce a composite with high density of surface defects. To investigate the influence of thermal treatment on the physical properties, and consequently on photoactivity, the composite has been traditionally annealed at 400 and 700 °C. The phase purity, crystal structure and average crystallite size of pristine metal oxides and the composites were investigated by X-ray diffraction and Raman spectroscopy. The particles morphology and size distributions were studied by FE–SEM and laser diffraction particle size analyzer, respectively. The textural properties were determined from N¬2¬ adsorption/desorption experiments, while the optical properties were studied using UV–Vis diffuse reflectance and photoluminescence spectroscopy. Photocatalytic activity of pristine ZnO and ZnO/SnO2 composites were examined via de-colorization of methylene blue under: (1) direct natural sunlight, and (2) artificial UV irradiation. In both cases enhanced photocatalytic activity of ZnO/SnO2 has been found. Enhanced photocatalytic activity can be attributed to the surface defects and to created ZnO/SnO2 heterojunctions which reduced electron-hole recombination time

Numerical study of the supercontinuum generation in the telecommunications windows in photonic crystal fiber

This research explores a supercontinuum (SC) generation in silica based highly nonlinear photonic crystal fiber of near infrared window, suitable for application in the field of telecommunications [1]. Results obtained here could be of interest in attempts to improve the characteristics of multi-wavelength sources for dense wavelength division multiplexing (DWDM) systems. We study numerically SC dynamics in both spectral and temporal domain in three different optical windows, at referent wavelengths of 835nm, 1300nm and 1550 nm. The dependence of SC properties on the input pulse power, shape and the value of the chirp is investigated in details. It has been shown that the most intense spread of SC spectrum at fiber output is obtained in the third optical window, while the input signal shape, power and duration stayed unchanged [2]. The shape of the initial pulse was the most influential in the second optical window, where the simulated SC has flat and smooth profile, covering the wavelength range from 1000 nm to 2000 nm. In addition, we examine the SC spectrum coherence in all of the three optical windows with respect to different input pulses. On the other hand, the richest SC dynamics is observed in the first window, where the appearance of high intensity events of the rogue wave type is reported [3].VII International School and Conference on Photonics : PHOTONICA2019 : Abstracts of Tutorial, Keynote, Invited Lectures, Progress Reports and Contributed Papers; August 26-30; Belgrad

Sunlight-driven Photocatalytic and Photo-electrochemical Activity of ZnO/SnO2 Composite

Due to their high photoactivity, photostability, chemical inertness, simple syntheses procedures as well as low cost, semiconductor materials such as TiO2, ZnO, V2O5, and SnO2, are recognized as materials with a great potential for photoelectrochemical and photocatalytic applications. In particular, they can be used as photoanode in the process of photoelectrolysis of water, or to initiate decomposition of different organic or biological pollutants in water under light irradiation. Which wavelength of light will be absorbed depends on the semiconductor band gap; semiconductors with a wide band gap (> 3 eV) can absorb light in the UV range only, while those with a narrow band gap (< 3 eV) can be activated by visible light. Current trend in photo(electro)catalysis is to develop efficient semiconductors which can be activated by absorbing natural sunlight. During the years, various approaches have been developed to modify optical properties of semiconductors thus to be capable to absorb sunlight, for example: the incorporation of transition metal ions or defects into the crystal structure, the particles’ surface sensitization, hydrogenation, coupling of semiconductors with different band gap energies, etc

Localized modes in linear flux dressed two-dimensional plus lattice

Flatband (FB) photonic lattices represent ideal testbed for studying transport and localization properties at the linear level in diverse physical systems [1]. Photonic lattices are easy for manipulation and investigation of wave dynamics. The photonic lattices offer an ability to design artificial gauge field effects which are equivalent to the magnetic field flux and the spin-orbit interaction in atomic systems [2]. The two-dimensional (2D) plus lattice [3] dressed by the artificial flux can be experimentally realized by techniques based on the coupled-spring resonators [4] and wave-guide networks [5]. Here we tuned the artificial flux values and studied their effect on the energy band spectrum and we were trying to find compact localized modes (CLMs). The geometry of the uniform plus lattice dressed by the artificial flux is Figure 2. Schematic of 2D plus-like lattice with artificial flux. The unit cell is encircled by a dotted line.schematically presented in Fig. 1. The unit cell consists of five sites, linearly coupled with each other with the same intra-cell coupling constant. The flux of the artificial field modifies the coupling between different unit cell sites to t∙exp(±iϕ/4), where t is the hopping parameter and ϕ is the artificial flux. In the absence of flux, in the uniform lattice, the energy spectrum has one fully degenerate FB, centered at zero, and four dispersive bands (DBs) [3]. We have found that this lattice can host the Aharonov-Bohm effect for certain flux values [6]. When diamond plaquettes are dressed by artificial flux ϕ=π, this lattice spectrum is described by two momentum independent, fully degenerated FBs, and three DBs. Corresponding CLMs have been obtained. In the comparison with the flux-free case, we found three different types of fundamental nonorthogonal CLMs now. These CLMs occupy 5 unit cells i.e. are class U=5. The central site amplitude is zero and all other 4 sites of unit cell have nonzero amplitudes.XVI Photonics Workshop : Book of abstracts; March 12-15, 2023; Kopaonik, Serbi

The influence of nonlinear and linear defects on the light propagation through linear one-dimensional photonic lattice

In this paper, the light beam propagation through one-dimensional photonic lattice, possessing one nonlinear defect and one linear defect, has been investigated numerically. Different dynamical regimes have been identified in terms of the distance between the two defects, position of the incident light beam, the width of linear defect, the values of nonlinearity and presence of the transverse kick. Strong localized modes on the defects, breathing and zig-zag modes in the area between defects have been observed. It has been concluded that the width of the linear defect placed next to the nonlinear one influences localization of the beam at the nonlinear waveguide. On the other hand, the nonlinear defect, regardless of the values of nonlinearity, have a small influence on the beam propagation in photonic lattice. It has been observed that the transverse kick of the initial beam leads to the distortion of localized structures. By launching the light beam towards defects, the reflection of light has been noticed. Presented results can be useful for different applications, such as blocking, filtering and routing of light beam through optical media

BT/ZnO composite materials with improved functional properties

Due to a high-power conversion efficiency (PCE), perovskite solar cells (PSCs) are the most developing area of research in the past decade. Although lead−based inorganic−organic PSCs has achieved the highest PCE of 25.2%, the toxic nature of lead and poor stability of organic components strongly limits its commercialization. This problem can be overcome by developing of inorganic perovskites with a high PCE. Barium titanate (BaTiO3, BT) belongs to the perovskite crystal structure materials with remarkable dielectric, ferroelectric and ferromagnetic properties. In this research, to enhance functional properties of BT we employed functionalization with MEMO silane followed by in-situ alloying with ZnO in different BT to ZnO wt.%. Synthesized ZnO@MEMO@BT composites were tested as photo- and photo-electro catalysts under simulated sunlight irradiation. An enhanced catalytic activity of ZnO@MEMO@BT composites, compared to pure BT is probably due to the modified binding energy and an optimized band structure. In order to investigate the origin of improved catalytic efficiency, pristine BT and composites were characterized using a variety of techniques, including X-ray powder diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), UV-Vis diffuse reflectance and photoluminescence spectroscopy. The enhanced photo(electro)catalytic activity of the composite materials can be attributed to the synergetic effect of the surface defects and the ZnO/BT heterojunction particles, which enabled charge separation, thereby hindering the recombination of photogenerated carriers

Enhanced natural sunlight- and artificial UV-driven photocatalytic activity of mechanically activated ZnO/SnO2 composite

Over the past four decades there is an increasing interest to develop highly efficient semiconductor photocatalysts for degradation of organic and biological pollutants in water under light irradiation. The semiconductor band gap determines which wavelength of light will be absorbed; precisely, semiconductors with a wide band gap (> 3 eV) can absorb only UV light, while those with a narrow band gap (< 3 eV) can be activated by visible light.In this study we examined structural, morphological, textural and optical properties of ZnO/SnO2 composite as potential photocatalyst. Mechanical activation of commercial ZnO and SnO2 powders has been used to produce a composite with high density of surface defects. To investigate the influence of thermal treatment on the physical properties, and consequently on photoactivity, the composite has been traditionally annealed at 400 and 700 °C. The phase purity, crystal structure and average crystallite size of pristine metal oxides and the composites were investigated by X-ray diffraction and Raman spectroscopy. The particles morphology and size distributions were studied by FE–SEM and laser diffraction particle size analyzer, respectively. The textural properties were determined from N¬2¬ adsorption/desorption experiments, while the optical properties were studied using UV–Vis diffuse reflectance and photoluminescence spectroscopy. Photocatalytic activity of pristine ZnO and ZnO/SnO2 composites were examined via de-colorization of methylene blue under: (1) direct natural sunlight, and (2) artificial UV irradiation. In both cases enhanced photocatalytic activity of ZnO/SnO2 has been found. Enhanced photocatalytic activity can be attributed to the surface defects and to created ZnO/SnO2 heterojunctions which reduced electron-hole recombination time

Strong coupling regime of semiconductor quantum dot embedded in the nano-cavity

Photonic lattices represent suitable systems for investigation of wave propagation in periodic structures [1]. However, different unavoidable defects may arise either during their process of fabrication or as result of misusage, accidental damage, etc. Although undesirable in the first place, these imperfections enable the existence of different types of stable, localized defect modes [2]. In this paper, we investigate light propagation through composite photonic lattice composed of two identical linear and lossless lattices. The interface between them represents a geometric defect, while each lattice contains a single nonlinear defect that is placed symmetrically with respect to the interface. Depending on the input light beam parameters (its position, width and transverse tilt), the width of geometric defect, strength and position of the nonlinear defects, different dynamical regimes have been identified. These dynamical regimes are caused by the balance of photonic lattice potentials’ contributions originating from the presence of the geometric and two nonlinear defects. We have found numerically conditions under which dynamically stable bounded modes can exist in the area between nonlinear defects or between a nonlinear and a geometric defect. Various types of localized modes such as: two-hump, multi-hump, one- and multicomponent moving breathers localized at a certain area among defects have been observed. The parameters can be adjusted to capture light and to prevent light launched inside the area among defects to leave it, i.e. this corresponds to the appearance of the modes trapped inside this area. Since the configuration of the lattice prevents transmission of the light through the area confined by defects, these modes can formally be related to Fano resonances and Fano- blockade [3, 4]. When light is launched outside the area among defects, different dynamical regimes have been distinguished: total reflection, single and double partial reflection and full transmission through the area among defects. These numerical findings may lead to interesting applications such as blocking, filtering and transporting light beams through the optical medium. Photonic devices based on resonant tunneling such as waveguides interacting through the area between defects, may be applied as add-drop filters.V International School and Conference on Photonics and COST actions: MP1204, BM1205 and MP1205 and the Second international workshop "Control of light and matter waves propagation and localization in photonic lattices" : PHOTONICA2015 : book of abstracts; August 24-28, 2015; Belgrad

Enhancement of ZnO@RuO2 bifunctional photo-electro catalytic activity toward water splitting

Catalytic materials are the greatest challenge for the commercial application of water electrolysis (WEs) and fuel cells (FCs) as clean energy technologies. There is a need to find an alternative to expensive and unavailable platinum group metal (PGM) catalysts. This study aimed to reduce the cost of PGM materials by replacing Ru with RuO2 and lowering the amount of RuO2 by adding abundant and multifunctional ZnO. A ZnO@RuO2 composite in a 10:1 molar ratio was synthesized by microwave processing of a precipitate as a green, low-cost, and fast method, and then annealed at 300°C and 600°C to improve the catalytic properties. The physicochemical properties of the ZnO@RuO2 composites were investigated by X-ray powder diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), UV-Vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The electrochemical activity of the samples was investigated by linear sweep voltammetry in acidic and alkaline electrolytes. We observed good bifunctional catalytic activity of the ZnO@RuO2 composites toward HER and OER in both electrolytes. The improved bifunctional catalytic activity of the ZnO@RuO2 composite by annealing was discussed and attributed to the reduced number of bulk oxygen vacancies and the increased number of established heterojunctions