We proposed a spectrally tunable photonic crystal (PC) cavity that is also relocatable spatially. The PC cavity is formed by setting a microsized dielectric sphere on a defect-free PC slab at a desired point. The resonant wavelength of the PC cavity can be tuned from 1343 to 1725 nm by changing the parameters of the sphere, e.g., the radius or the refractive index. In addition, the wavelength is also adjusted finely (∼5  nm) by moving the sphere upward.

We report the use of dielectrophoresis to fabricate in-situ probes for tip-enhanced Raman spectroscopy (TERS) based on Au nanoparticles. A typical conductive atomic force microscope (AFM) was used to functionalize iridium-coated conductive silicon probes with Au nanoparticles of 10-nm diameter. Suitable TERS probes can be rapidly produced (30 to 120 s) by applying a voltage of 10 Vpp at a frequency of 1 MHz. The technique has the advantage that the Au-based probes are ready for immediate use for TERS measurements, minimizing the risks of tip contamination and damage during handling. Scanning electron microscopy and energy dispersive x-ray spectroscopy were used to confirm the quality of the probes, and used samples of p-ATP monolayers on silver substrates were used to demonstrate experimentally TERS measurements.

This PDF file contains the editorial “Special Section Guest Editorial: Advances in Nanostructured Thin Films” for JNP Vol. 10 Issue 03

To reduce the intensity of the Fresnel reflections of optical components, subwavelength structures prepared by reactive ion etching of SiO₂ thin films were combined as the outermost layer with a multilayer system made of conventional thin-film materials. A hybrid coating was thus realized, with the nanoscaled structured outermost layer expected to further improve the antireflection properties of common interference stacks. The microscopic and optical spectroscopic analysis of the subwavelength structures revealed that pillar-shaped nanostructures formed during etching exhibit low-refractive-index properties and have a depth-dependent refractive index. To take into account the refractive-index gradient in the coating design, the optical properties of the nanostructures were modeled using the effective-medium approximation. The calculated average effective refractive index turned out to be 1.11 at 500-nm wavelength. A hybrid coating was designed to minimize the residual reflectance in the 400-nm to 900-nm spectral range for BK7 glass substrate. Experimental results demonstrated that the hybrid-coating approach yields a low residual reflectance with very good omnidirectional properties, owing to the properties of the nanostructured surface.

Direct laser interference patterning of polyimide (PI) films was performed by using a pulsed 355-nm laser. At laser fluence of 0.4  J/cm², gratings with spatial periods of 3.8  μm to 344 nm were created. The highest aspect ratio of the grating structure (0.8) was obtained for the 344-nm grating. An all-polymer dye laser was then fabricated by spin-coating a layer of disodium fluorescein (DF)-doped polyvinyl alcohol (PVA) film on bare and patterned PI substrate. Green laser emission was obtained when transversely pumped by a 355-nm laser. The lasing threshold reduced by ∼10 times for the sample with 344-nm grating while the laser intensity was ∼18 times higher. The enhancements are ascribed to the 344-nm grating structures, which act as an efficient distributed feedback resonator and distributed Bragg reflector grating for DF-doped PVA emitting at ∼563  nm, on top of being a passive light-trapping structures.

A topological insulator is classically modeled as an isotropic material with a magnetoelectric pseudoscalar Ψ existing in its bulk while its surface is charge free and current free. An alternative model is obtained by setting Ψ≡0 and incorporating surface charge and current densities characterized by an admittance γ. Analysis of planewave reflection and refraction due to a topological-insulator half space reveals that the parameters Ψ and γ arise identically in the reflection and transmission coefficients, implying that the two classical models cannot be distinguished on the basis of any scattering scenario. However, as Ψ disappears from the Maxwell equations applicable to any region occupied by the topological insulator, and because surface states exist on topological insulators as protected conducting states, the alternative model must be chosen.

The substrate cooling method was used in glancing angle deposition to grow a slanted silver nanorod array (NRA). Liquid nitrogen was allowed to flow under the substrate during deposition, and we compared the morphologies of Ag NRAs deposited with and without cooling. The cooling reduced the average width of the nanorods. A Z-shaped nanostructure array composed of three sections of silver NRAs was then deposited under the same cooling conditions. The average tilt angle of the nanorods from the surface normal was varied from the bottom section to the top section with the nanorods of the top section made to lie almost parallel to the substrate. Under normal illumination, the rods in the top section exhibit distinct longitudinal and transverse plasmon modes that cause strong polarization-dependent transmittance and reflectance.

The rapid switching of flow direction in a thin microfluidic chamber filled with water is demonstrated using the thermoplasmonic Marangoni effect. A gold island film is used as a thermoplasmonic heater on which a continuous-wave laser is focused to generate a microbubble and develop Marangoni flows around it. The direction of the observed flow significantly changes depending on the laser power. When the laser power is square-wave modulated, the flow direction instantaneously switches in response to the power, creating a discrete pattern of polystyrene microspheres. Flow direction-switching is observed for laser power modulation frequencies of up to 40 Hz, which indicates that the time constant of the flow direction switching is on the order of at least several milliseconds. This rapid flow direction switching is attributed to the fast response of both the thermoplasmonic effect of the gold nanoparticles and the Marangoni effect on the bubble surface.

Cadmium oxide (CdO) thin films with low electrical resistivity and higher transparency have been deposited by radiofrequency (RF) magnetron sputtering on glass substrates. Sputtering process was carried out at RF power of 40 W and with varying substrate temperatures. The structural, morphological, electrical, and optical properties of the deposited films are investigated. The structural properties reveals that the as-deposited CdO films shows preferential orientation along (111) plane exhibiting face centered cubic structure. The surface morphology shows that all the films possess well defined grain boundaries with high uniformity. CdO samples deposited at substrate temperature of 150°C with RF power of 40 W exhibits above 95% transparency within the visible wavelength with lower electrical resistivity value in the order of 10⁻⁵  Ω·cm. The Raman spectroscopy analysis reveals the possible modes present in CdO films and its dependence on substrate temperature. The comparatively high value of the figure of merit for the optimum sample of CdO deposited at 150°C indicates that these films are suitable for optoelectronic device applications.

Multiple surface-plasmon-polariton (SPP) waves at a single free-space wavelength can be guided by the interface of a metal and a chiral sculptured thin film (STF). Multilayers comprising a chiral STF of lanthanum fluoride deposited on an aluminum thin film deposited on a glass substrate were fabricated. In some chips, a 5-nm-thick layer of silver nanoparticles was deposited at one of two selected depths in the chiral STF. The chips were then deployed in a prism-coupled configuration in a custom-built machine for surface multiplasmonic resonance imaging (SMPRI), in order to observe the effects of the silver-nanoparticle layer on the multiple SPP-wave modes. The angular locations of the SPP-wave modes were found to be not greatly dependent on whether the silver-nanoparticle layer was deposited after the first or the second period of a three-periods-thick chiral STF. With aqueous solutions of sucrose as infiltrant fluids, the angular shifts of the SPP-wave modes were determined as the refractive index of the infiltrant fluid increased. The use of a charge-coupled devices camera and upgraded motion-control equipment for SMPRI was found to increase the sensitivity of the chip. The silver-nanoparticle layer was also found to enhance the sensitivity.

The free-electron relaxation time is a crucial property to be considered in the design of optical devices, because it determines the dielectric function. Thus, an accurate understanding of this relaxation time is essential for design optimization. Some simulations showed that the relaxation times of Au thin films with thicknesses below 30 nm are different from those of the bulk material. Therefore, we deposited films with four different thicknesses below this value and used near-infrared spectroscopic ellipsometry to show that the relaxation time is dependent on the film thickness. We fitted the ellipsometry spectrum of Au thin films with a thickness <30  nm and found the imaginary part of the dielectric function of the thin films to vary with the film thickness in the near-infrared region. Furthermore, different relaxation times were used to simulate the reflectance of a Fabry–Pérot absorber and a plasmonic metamaterial absorber. The simulation results indicated that the obtained relaxation time enables a more reliable evaluation of optical device design.

This PDF file contains the editorial “Special Section Guest Editorial: Optics, Spectroscopy, and Nanophotonics of Quantum Dots” for JNP Vol. 10 Issue 03

This work reports on a chemical beam epitaxy growth study of InGaAs/GaAs quantum dots (QDs) engineered using an in-situ indium-flush technique. The emission energy of these structures has been selectively tuned over 225 meV by varying the dot height from 7 to 2 nm. A blueshift of the photoluminescence (PL) emission peak and a decrease of the intersublevel spacing energy are observed when the dot height is reduced. Numerical investigations of the influence of dot structural parameters on their electronic structure have been carried out by solving the single-particle one-band effective mass Schrödinger equation in cylindrical coordinates, for lens-shaped QDs. The correlation between numerical calculations and PL results is used to better describe the influence of the In-flush technique on both the dot height and the dot composition.

The problem of finding effective characteristics of the nanostructure consisting of spherical shells (nanomatryoshka) is solved using the matrix homogenization method. According to the problem formulation, each of the system layers possesses piezoelectric and/or piezomagnetic properties. Thus, the mutual influence of the elastic, electrical, and magnetic characteristics of the shells on their homogenized values is investigated. In particular, the dependence of the dielectric and magnetic permittivity on the geometrical parameters of the layers is studied and analyzed. The performance of the model is illustrated for a two-layer structure.

The dynamics of the density of indirect excitons created in a double quantum well heterostructure by a laser illumination are considered and an idea of a generator of the traveling pulses of the excitonic condensed phase functioning at steady pumping is suggested. The setup of the proposed system includes a narrow highly illuminated region and a broad moderately illuminated region that supports the propagation of islands of the condensed phase. Simulation predicts that despite the steady pumping, the islands are formed periodically over time at the boundary of these regions and move due to the external potential bias. The calculations are based on the model of high density excitonic systems approbated by the explanations of multiple experiments. The generation of pulses occurs if both the uniform and nonuniform solutions for the exciton density exist in the propagation region. The range of the pumping intensity and the threshold for the potential bias for the generation are determined.

The effect of photosensitization of IR luminescence excitation (1205 nm) of colloidal Ag₂S quantum dots (QDs) with average size of 2.5±0.6  nm in gelatin at 600 to 660 nm by molecules of 3,3’-di-(γ-sulfopropyl)-4,4’,5,5’-dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt (Dye1) and thionine dye (Dye2) was registered. Cis-J-aggregates of Dye1 and cations monomer of Dye2 conjugated with Ag₂S QDs take part in this process. The photosensitization of luminescence excitation of colloidal Ag₂S QDs was interpreted by resonance nonradiation transfer of electronic excitation energy from cis-J-aggregates of Dye1 and cations of Dye2 to centers of recombination luminescence of Ag₂S QDs.

UV-Vis absorption of colloidal cadmium sulfide quantum dots (QDs) synthesized by an aqueous synthesis in a gelatin matrix was investigated. Using the dipole approximation, taking into account the Coulomb interaction between the electron and hole in a QD and the polarization effects on the spherical boundary of QD and matrix, it was found the change of selection rules for optical transitions. It is shown that the optical absorption edge of QDs is formed by two optical transitions of electron between low-excited levels of size quantization of heavy hole (1S_3/2 and 2S_3/2), located in QDs valence band and fundamental size-quantized states 1S_e of conduction band. These transitions are identical in intensity. Estimations of average values of CdS QDs radius were realized using the developed formalism for UV-Vis absorption spectra. These data were compared with experimental values of this parameter, obtained using transmission electron microscope.

Aqueous synthesis of mixed cadmium and zinc sulfides colloidal quantum dots (QDs) has been successfully realized. Colloidal Cd_xZn₁−_xS QDs are formed in a cubic crystal lattice with particle size of ∼2  nm. The blueshift of optical absorption spectra from 420 to 295 nm and recombination photoluminescence from 646 to 483 nm with increasing zinc content in QDs was observed. Optimum photoluminescence intensity occurs for QDs with Cd_0.3Zn_0.7S composition. With increasing zinc content up to Cd_0.3Zn_0.7S, luminescence intensity increases and decreases when zinc content is larger than 0.7. The increase in photoluminescence intensity is explained by the increase in the number of point defects, such as complexes of interstitial metal atoms–metal vacancies [Me_i−V_Me]. Such complexes occur due to displacement of the metal atom at the center of the elementary tetrahedron due to substitution of one of the four sulfur atoms by an impurity atom, such as an oxygen atom.

Electronic states and direct interband light absorption in the ensemble of prolate spheroidal quantum layers are considered. The problem of finding the one-electron wave function and energy spectrum have been solved exactly. Absorption edge dependence on the thickness of the layer in the strong size quantization regime has been obtained. The effect of nonparabolicity of the dispersion law of energy levels and optical absorption have been taken into account and calculations are carried out for the cases of both parabolic and Kane’s dispersion laws. Selection rules have been revealed. Absorption coefficient dependence on the frequency of incident light has been obtained, taking into account dispersion of nanolayer thicknesses for the cases of both symmetric and asymmetric distribution functions.

We present a combined experimental and simulation study of a single self-assembled InGaAs quantum dot coupled to a nearby (∼25  nm) plasmonic antenna. Microphotoluminescence spectroscopy shows a ∼2.4× increase of intensity, which is attributed to spatial far-field redistribution of the emission from the quantum dot-antenna system. Power-dependent studies show similar saturation powers of 2.5  μW for both coupled and uncoupled quantum dot emission in polarization-resolved measurements. Moreover, time-resolved spectroscopy reveals the absence of Purcell enhancement of the quantum dot coupled to the antenna as compared with an uncoupled dot, yielding comparable exciton lifetimes of τ∼0.5  ns. This observation is supported by numerical simulations, suggesting only minor Purcell-effects of <2× for emitter–antenna separations <25  nm. The observed increased emission from a coupled quantum dot–plasmonic antenna system is found to be in good qualitative agreement with numerical simulations and will lead to a better understanding of light–matter coupling in such semiconductor–plasmonic hybrid systems.

Here, we report the studies of thermal treatment effect on the structural and optical properties of nanocomposites based on cadmium sulfide quantum dots embedded in a silicate matrix. An explanation of the mechanism of reversible photoinduced absorption of the nanocomposite has been given. It is found that heating at 180°C results in significant changing of nanocomposite absorption and luminescence spectra caused by structural changes of quantum dots. It is found that photoinduced optical absorption of the nanocomposite is caused by amorphous-structured cadmium sulfide quantum dots.

A surface plasmon polariton is an electromagnetic wave that propagates along an interface between two materials with dielectric permittivity of opposite signs. Such waves can be focused by metal waveguides of special geometry. The spatial distribution for a near-field strongly depends on a linear chirp of the laser pulse, which can partially compensate the wave dispersion. Field distribution is calculated for different chirp values, opening angles, and distances. The spatial selectivity of excitation of quantum dots using focused fields is shown using Bloch equations.

The frequency dependence of the capacitance variation between dark and near-infrared-modulated illumination conditions is measured for metal-oxide-semiconductor structures with germanium nanocrystals embedded in a thick SiO₂ film grown on a silicon substrate. The results have shown that the device is expected to be sensitive at high frequencies (up to 111 GHz) making it a good candidate for optoelectronic high-speed use and for optical communication applications.

This study introduces the application of ceria nanoparticles (NPs) as an optical sensor for peroxide using fluorescence quenching technique. Our synthesized ceria NPs have the ability to adsorb peroxides via its oxygen vacancies. Ceria NPs solution with added variable concentrations of hydrogen peroxides is exposed through near-UV excitation and the detected visible fluorescent emission is found to be at ∼520  nm. The fluorescent intensity peak is found to be reduced with increasing the peroxide concentrations due to static fluorescence quenching technique. The relative intensity change of the visible fluorescent emission has been reduced to more than 50% at added peroxide concentrations up to 10 wt. %. In order to increase ceria peroxides sensing sensitivity, lanthanide elements such as samarium (Sm) are used as ceria NPs dopant. This research work could be applied further in optical sensors of radicals in biomedical engineering and environmental monitoring.

The stresses in thin films are one of the main problems in the development of small dimensions or thin optical components. In order to produce low-tension anisotropic coatings, the characterization of serial bideposition is essential. Structural and optical performance have been tested for anisotropic TiO₂ thin films deposited by serial bideposition technique. Three-dimensional surface interferometric measurements were performed for samples deposited at various angles. Also experimental observations of anisotropic tensions in annealed two-dimensional sculptured thin films of TiO₂ material are presented. The deposition angle of 80 deg is considered to be the most applicable for developing optical components due to the befitting optical performance and the lowest tensions before and after the annealing.

We achieved considerable laser diode (LD) improvement after annealing InGaP/InAlGaP laser structure at 950°C for a total annealing time of 2 min. The photoluminescence intensity is increased by 10 folds and full-wave at half-maximum is reduced from ∼30 to 20 nm. The measured LDs exhibited significantly reduced threshold current (Ith), from 2 to 1.5 A for a 1-mm long LD, improved internal efficiency (ηi), from 63% to 68%, and increased internal losses αi, from 14.3 to 18.6  cm−1. Our work suggests that the use of strain-induced quantum well intermixing is a viable solution for high-efficiency AlGaInP devices at shorter wavelengths. The advent of laser-based solid-state lighting (SSL) and visible-light communications (VLC) highlighted the importance of the current findings, which are aimed at improving color quality and photodetector received power in SSL and VLC, respectively, via annealed red LDs.

We propose a hybrid graphene molybdenum disulphide-based photoconductive antenna to overcome the restrictions of metallic photoconductive antennas and graphene-based photoconductive antennas, simultaneously. The structure is composed of a hybrid graphene-MoS₂ strip as the antenna deposited on a low-temperature gallium arsenide substrate. A full-wave electromagnetic solver, namely, high frequency structural simulator (HFSS) is used to analyze the whole structure. It is shown that the proposed photoconductive antenna provides us with not only high input impedance and reconfigurability but also high values of matching efficiency and radiation efficiency. The impact of increasing MoS₂ layers on the performance of the antenna is also investigated.

The energy spectrum of the two-dimensional cavity magnetoexciton-polaritons has been investigated previously, using exact solutions for the Landau quantization (LQ) of conduction electrons and heavy holes (hhs) provided by the Rashba method. Two lowest LQ levels for electrons and three lowest Landau levels for hhs lead to the construction of the six lowest magnetoexciton sates. They consist of two dipole-active, two quadrupole-active, and the two forbidden quantum transitions from the ground state of the crystal to the magnetoexciton states. The interaction of the four optical-active magnetoexciton states with the cavity-mode photons with a given circular polarization and with well-defined incidence direction leads to the creation of five magnetoexciton-polariton branches. The fifth-order dispersion equation is examined by using numerical calculations and the second-order dispersion equation is solved analytically, taking into account only one dipole-active magnetoexciton state in the point of the in-plane wave vector k→∥=0. The effective polariton mass on the lower polariton branch, the Rabi frequency, and the corresponding Hopfield coefficients are determined in dependence on the magnetic-field strength, the Rashba spin–orbit coupling parameters, and the electron and hole g-factors.

This paper describes a minimally invasive method for detection and growth inhibition of tumors that utilizes the unique properties of super paramagnetic nanoparticles. To demonstrate the feasibility of this method, dimercaptosuccinic acid-coated magnetite nanoparticles were successfully fabricated and used. Those nanoparticles were simultaneously used for magnetoacoustic detection of tumors and for specific hyperthermia treatment in C57BL/J mice injected with Lewis lung carcinoma cells. The in vivo acoustic signal attributed to the nanoparticles was 4.4 dB, while the single session hyperthermia treatment caused a reduction of 50% in tumor growing rate. In addition, a thermography-based method was applied to monitor the efficacy of the hyperthermia treatment. The presented method has the potential to revolutionize current cancer treatment by enabling diagnosis and treatment under real-time feedback in one session.

It has been found that the formation of a biexciton in a nanoheterostructures (NHS) made up of aluminum oxide quantum dots (QDs) synthesized in a dielectric matrix is of threshold character and can occur in a nanosystem, where the distance D between the surfaces of QD is given by the condition D_c⁽¹⁾≤D≤D_c⁽²⁾. We have shown that with such an NHS acting as “exciton molecules” (biexcitons consisting of spatially separated electrons and holes) are the QDs of aluminum oxide with excitons localizing over their surfaces. The position of the biexciton state energy band depends both on the mean radius of the QDs, and the distance between their surfaces, which enables one to purposefully control it by varying these parameters of the nanostructure.

The width of spiral-patterned zinc oxide (ZnO) nanorod coatings on plastic optical fiber (POF) was optimized theoretically for light-side coupling and found to be 5 mm. Structured ZnO nanorods were grown on large core POFs for the purpose of alcohol vapor sensing. The aim of the spiral patterns was to enhance signal transmission by reduction of the effective ZnO growth area, thereby minimizing light leakage due to backscattering. The sensing mechanism utilized changes in the output signal due to adsorption of methanol, ethanol, and isopropanol vapors. Three spectral bands consisting of red (620 to 750 nm), green (495 to 570 nm), and blue (450 to 495 nm) were applied in measurements. The range of relative intensity modulation (RIM) was determined to be for concentrations between 25 to 300 ppm. Methanol presented the strongest response compared to ethanol and isopropanol in all three spectral channels. With regard to alcohol detection RIM by spectral band, the green channel demonstrated the highest RIM values followed by the blue and red channels, respectively.

The transmission properties of a one-dimensional graphene-based Thue–Morse quasiperiodic structure in which graphene nanolayers are embedded between dissimilar adjacent dielectric layers have been investigated. From the numerical results performed by transfer matrix method, it is found that the structure possesses an omnidirectional photonic bandgap called a graphene-induced photonic bandgap (GIPBG) due to the existence of the graphene nanolayers, in addition to the structural Bragg gaps. To design an omnidirectional broadband THz filter, the effects of many parameters such as the scale length and relative permittivity of the layers on the properties of GIPBG are discussed. Our findings show that the frequency range of the omnidirectional GIPBG increases as the scaling decreases. In contrast to Bragg gaps, the width of such an omnidirectional bandgap is notably enhanced by reducing the contrast of the layers’ permittivity and reaches a maximum value when the constituent layers have the same relative permittivity. Our investigations also reveal that in the case of a uniform material, the lowest permittivity of the dielectric material would result in the widest omnidirectional GIPBG. Moreover, the possibility of external control of the omnidirectional bandwidth using a gate voltage is shown. Finally, the application of the structure as a polarizing beam splitter has been shown.

A biosensor is a device that is used to detect the analytes or molecules of a sample by means of a binding mechanism. A two-dimensional photonic crystal waveguide-based biosensor is designed with a diamond-shaped ring resonator and two waveguides: a bus waveguide and a drop waveguide. The sensing mechanism is based on change in refractive index of the analytes, leading to a shift in the peak resonant wavelength. This mechanism can be used in the field of biomedical treatment where different body fluids such as blood, tears, saliva, or urine can be used as the analyte in which different components of the fluid can be detected. It can also be used to differentiate between the cell lines of a normal and an unhealthy human being. Average value of quality factor for this device comes out to be 1082.2063. For different analytes used, the device exhibits enhanced sensitivity and, hence, it is useful for the detection of diseases.

Photonic devices used in photonic integrated circuits are very important to understand high performance devices. To increase reliability of these devices, temperature characteristics of these devices need to be investigated. Still, no device that can simply sense temperature change in microscale exists. Hence, we have designed microscale plasmonic devices for temperature change sensing at the wavelength of near 633 nm. The designed device consists of a single- and a multimode plasmonic channel waveguide with two different trench depths. The designed device utilizes multimode interference of channel plasmon polaritons for sensing temperature change. The designed device can be applied in the range of the temperature change that silver coefficient of thermal expansion does not greatly change, such as the temperature from room temperature to ±30°C. The temperature change sensitivity of the designed device has been numerically confirmed by the finite-difference time-domain method. The temperature change sensitivity of the designed device is a little inferior to that of existing temperature sensing devices. However, the designed device can be realized under one hundredth of the size of existing temperature change sensing devices.

Reducing active layer thickness of solar cell stresses on efficient light trapping mechanisms to keep the cell efficiency intact. Directional light scattering and promising refractive index of silicon nanoparticles make them encouraging scattering centers for thin-film silicon solar cells. Finite-difference time-domain simulations are used to study the optical properties of silicon nanospheres embedded in the top and bottom buffer layer of solar cells. Diameter of a silicon nanoparticle plays a crucial role in the forward and backward scattering of incident light into the cell. Silicon nanospheres outperform commonly used metallic and dielectric nanospheres and trapped the incident light over a broad spectrum. Silicon nanospheres require special attention when placed in both the buffer layers of the solar cell simultaneously, and lateral displacement of the silicon nanospheres at the top buffer layer with respect to nanospheres at the bottom buffer layer is beneficial. Lateral displacement of nanospheres provides a total quantum efficiency of 51.49% in comparison to 21.9% of the pristine cell. These exceptional scattering competencies of silicon nanospheres make them a promising candidate for photovoltaic applications. Silicon scatterers may be used with well-established fabrication techniques.

We investigate linear and nonlinear optical properties of standard human ovarian cancer cells (cell line: A2780cp) in vitro. Cells were treated by graphene quantum dots (GQDs) with two special concentrations. Nontoxicity of GQDs was examined in standard biological viability tests. Cancerous cells were fixed on a glass slide; then, interaction of light with biofilms was studied in linear and nonlinear regimes. Absorption spectra of untreated biofilms and biofilms with two different concentrations of GQDs was studied by UV-visible spectrophotometer. Optical behavior of biofilms in a linear regime of intensity (with low-intensity laser exposure) was reported using a simple optical setup. After that, we compared the attenuation of light in biofilm of cancerous cells with and without GQDs. Nonlinear behavior of these biofilms was investigated by a Z-scan setup using a continued wave He–Ne laser. Results showed that GQDs decreased the extinction coefficient and changed the sign and exact value of the nonlinear refractive index of malignant ovarian cells noticeably. The nonlinear refractive index of studied cells with no GQDs treatment was in the order of 10⁻⁸  (cm²/w) with a positive sign. This quantity changed to the same order of magnitude with a negative sign after GQDs treatment. Thus, GQDs can be used for cancer diagnosis under laser irradiation.

This paper presents a method for modifying the point spread function (PSF) into a doughnut-like shape, through the utilization of the plasma dispersion effect (PDE) of silicon-coated gold nanoparticles. This modified PSF has spatial components smaller than the diffraction limit, and by scanning the sample with it, super-resolution can be achieved. The sample is illuminated using two laser beams. The first is the pump, with a wavelength in the visible region that creates a change in the refractive index of the silicon coating due to the PDE. This creates a change in the localized surface plasmon resonance wavelength. Since the pump beam has a Gaussian profile, the high intensity areas of the beam experience the highest refractive index change. When the second beam (i.e., the probe) illuminates the sample with a near-infrared wavelength, this change in the refractive index is transformed into a change in the PSF profile. The ordinary Gaussian shape is transformed into a doughnut shape, with higher spatial frequencies, which enables one to achieve super-resolution by scanning the specimen using this PSF. This is a step toward the creation of a nonfluorescent nanoscope.

We report a simple way of etching lithium niobate (LN) to build ridge waveguides. Argon plasma is used in an RF-sputtering chamber to etch the LN. The height of waveguide walls reaches 2.5  μm and a titanium self-alignment in-diffusion process is used to make the waveguide. Several diffusion times and different waveguides width are used to compare the mode properties and proportion of light that is confined in the ridge section of the waveguide.

A computational study of the third-harmonic (TH) generation (THG) and enhancement through an χ⁽³) process in one-dimensional nonlinear photonic crystals is presented in this paper. We have introduced a canonical variational problem with a small increment factor to solve the THG problem. The problem with a large input pump intensity or strong nonlinear susceptibilities can be handled by a versatile and accurate method, which combines finite-element methods and a continuation fixed-point iteration algorithm. The TH signal generation and enhancement through the direct χ⁽³⁾ process are displayed by two periodic structures. Numerical experiments show that the TH signal is significantly enhanced when the frequencies of the fundamental wave and the TH wave are turned to the corresponding photonic band edges to meet the phase-matching condition. Results of numerical experiments also indicate that our proposed method is computationally efficient and precise to handle strong nonlinearities, i.e., large values of input pump power.

We propose the use of one-dimensional semiperiodic front and back gratings based on Thue–Morse, Fibonacci, and Rudin–Shapiro (RS) binary sequences as promising photon management techniques for enhancing ultra-broadband optical absorption in thin-film solar cells. The semiperiodicity allows an aggregate light in-coupling into the active layer within the range of the solar spectrum that is less weak compared to an inherently broadband random grating, but has a much larger bandwidth than the strong in-coupling via a periodic grating configuration. The proper design procedure proposed here deviates from a canonical double grating synthesis as it adheres to an ultra-broadband design where the spectrally integrated absorption in the active material is the proper subject to optimization, leaving the grating perturbations just a measure to perturb and mold the trapped light field in the active layer accordingly. It is shown that by using a well-defined RS double grating in a 400-nm thick crystalline silicon solar cell, a 110.2% enhancement of the spectrally integrated optical absorption can be achieved relative to the reference case without grating.

A hybrid plasmonic waveguide with an alternative structure is presented in this paper, which consists of a silver cylindrical nanowire coated with a low-index dielectric silica layer attached on a silicon-on-insulator (SOI) substrate with a rectangular ridge. The effects of the silver nanowire, silica-coated layer, silicon substrate layer, and the ridge’s width to thickness ratio on the modal properties have been numerically investigated based on the finite-difference time-domain method. The simulation results demonstrate that the introduction of the low-loss dielectric-coated layer and the ridge of SOI substrate can greatly increase the propagation distance while maintaining strong confinement of light. The propagation distance as long as 660  μm and mode field with subwavelength confinement can be simultaneously realized at telecommunication wavelength. The proposed waveguide consisting of the silica-coated silver nanowire and the SOI ridge substrate would be a beneficial complement to the expanding family of hybrid plasmonic structures.

The nonlinear surface plasmon polariton (SPP) supported by a linear/metal-nonlinear slab waveguide was studied analytically. The dispersion conditions were obtained from fundamental Maxwell’s equations to determine the propagation characteristics of the nonlinear SPPs supported by the waveguide. The mode profile of the nonlinear mode was studied to analyze the physics behind the observed propagation characteristics. After studying propagation characteristics of the mode, the linear layer was replaced with a layer containing a uniaxial material. The effect of optical anisotropy of the layer on the dispersion characteristics of the nonlinear SPPs was investigated to understand the possible tunability of the mode. It has been observed that the propagation characteristics of modes supported by the waveguide can be tuned with the help of an anisotropic medium. The guiding structure could find application in the tunable components in all-optical integrated chips.