Search

Rational design of AuNST morphology requires adequate computational models. The bulk dielectric function is not applicable to sharp nanostar spikes. We suggest a two-component dielectric function in which the nanostar core is treated as a bulk material, whereas the size-corrected dielectric function of the spikes is treated by a modified Coronado-Schatz model. In addition to the strong broadening of plasmonic peaks, the simulated absorption and scattering spectra show unusual properties, which are not observed with bulk dielectric functions. The effect of NIR water absorption on nanostar spectra is small, and the absorption peak demonstrates the expected small decrease in the absorbing media. Surprisingly, however, water absorption increases the scattering peak by 30%. For the common surfactant-free Vo-Dinh AuNSTs, we report, for the first time, very intense SWIR plasmonic peaks around 1900 nm, in addition to the common strong peak in the UV-vis-NIR band (here, at 1100 nm). For bilayers of AuNSTs in air, we recorded two similarly intense peaks near 800 and 1500 nm. To simulate the experimental extinction spectra of colloids and bilayers on glass in air, we develop a statistical model that includes the major fraction of typical Vo-Dinh AuNSTs and two minor fractions of sea urchins and particles with protrusions. In contrast to the general belief, we show that the common UV-vis-NIR plasmonic peak of surfactant-free AuNSTs is related to short spikes on a spherical core, whereas long spikes produce an intense SWIR plasmonic mode. Such a structural assignment of vis-NIR and SWIR peaks does not seem to have been reported previously for surfactant-free nanostars. With our model, we demonstrate good agreement between simulated and measured spectra of colloids and bilayers on glass in air.

The results of the research and design of a novel vacuum photosensor with a planar molybdenum blade structure are presented. The advanced prototype implements the principle of an increasing penetrability of the Schottky barrier for the metal&ndash, vacuum interfaces under the action of an external strong electrostatic field. Theoretical and experimental substantiation of the photosensor performance in a wide range of wavelengths (from 430 to 680 nm and from 800 to 1064 nm) beyond the threshold of the classical photoelectric effect is given. The finite element method was applied to calculate distribution of the optical and electrostatic fields inside the photosensor structure. The sensor current-to-light response was studied using the periodic pulsed irradiation with the tunable wavelength. It was shown that the nanoscale localization zones of two types are formed near the surface of the blade tip: the zone of an increased concentration of hot electrons localized inside the molybdenum blade, and the zone with an increased strength of the external electrostatic field localized outside the blade. In general, the mutual positions of these zones may not coincide, whereas the position of the first-type localization zone significantly varies with the changes in the wavelength of the irradiating light. This causes features in the spectrum of the quantum yield of the photosensor such as expressed non-monotonic behavior and occurrence of sharp dips. The design of the photosensor that provides matching of the positions for both types of localization zones was proposed, the manufactured prototypes of the designed device were experimentally studied. In the designed photosensor, the ballistic transport of photoelectrons in the vacuum gap with a strong field provides a possibility for the creation of ultra-fast optoelectronic devices, such as modulators, detectors, and generators.

The consistent patterns for local temperature fields under laser irradiation of biological tissue doped by effectively absorbing plasmon gold nanostars are discussed. Differences in the degree of spatial localization and the kinetics of the photoinduced temperature fields under irradiation by femto-, pico- and nanosecond pulses are revealed.

In this work, we investigate the spectral and polarization characteristics of a vacuum photosensor with a nanoscale molybdenum blade as a sensing element. The results of theoretical and experimental studies of the optical fields in the sensor and the photocurrent produced by laser beam irradiation in the range of wavelengths from the visible to the near infrared are presented. The existence of a photo-response far beyond the red threshold of the classical photoelectric effect is ensured by the localization of an external strong electrostatic field. Features of the field interaction of radiation with a molybdenum blade cause the registered spectral non-monotonicity of the photocurrent value, which corresponds to the results of theoretical studies. The ballistic transport of electrons in a vacuum is characterized by a high speed. Achieved results made the photosensor based on nanoscale molybdenum blade promising in the development of ultrafast vacuum micro and nanoelectronic devices.

In this work, we describe the technology and design of planar multilayer structure. It is used as a sensitive element of the vacuum photosensor. Metal and dielectric layers are of nanoscale thickness. It is shown that the use of a thin molybdenum blade in the structure ensures the localization of the electrostatic field and increases the photosensitivity of the vacuum sensor. Submicron inter-electrode gaps provide a short transit time of the electron beam caused by the action of a light pulse. The ballistic transport of electrons in a vacuum is characterized by a high speed.

In this paper, a theoretical model of the formation of a local temperature field in suspensions of microorganisms with embedded plasmonic gold nanorods under irradiation by low-intensity NIR laser light was considered. The results of numerical modeling of the optical properties of plasmon nanorods used in the experiments, and the results of multiscale modeling of the parameters of local hyperthermia with various types of distribution of the concentration of plasmon nanoparticles are presented. Found that the process of concentration of nanoparticles, functionalized with human immune globulins IgA and IgG, around the cells of microorganisms with the formation of "clouds" leads to the appearance of a microscale zone of elevated temperature. This ensures a synergistic effect of a multiplicative increase in the volume of the hyperthermia zone. The results of numerical simulation provide a justification for the experimentally observed increase in the bacterium killing ability at laser hyperthermia of the cellular environment doped with functionalized nanoparticles, without a noticeable increment in the recorded average sample temperature when irradiated with a low intensity laser beam of around 100 mW/cm2.

Numerical modeling of spectral absorption and scattering properties of structures manufactured as the ordered arrays of plasmon nanoparticles is carried out in this work. The results of numerical 2D simulation of selective heating of an array of plasmon resonant gold nanodiscs irradiated by a CW NIR laser (810 or 1064 nm) are presented. Calculations fit well to experimental data received. We demonstrate the possibility to control the local amplification of a shining laser field in the space between nanodiscs, as well as plasmon resonance absorption of each individual nanodisc. The perspectives of application of such nanostructures for providing of precision dosed-up thermal effects in cells and biological tissues are discussed.

An important direction in the development of X-ray computed tomography sensors in systems with increased scanning speed and spatial resolution is the creation of an array of miniature current sources. In this paper, we describe a new material based on gold nanostars (GNS) embedded in nanoscale diamond-like carbon (DLC) films (thickness of 20 nm) for constructing a pixel current source with photoinduced electron emission. The effect of localized surface plasmon resonance in GNS on optical properties in the wavelength range from UV to near IR, peculiarities of localization of field and thermal sources, generation of high-energy hot electrons, and mechanisms of their transportation in vacuum are investigated. The advantages of the proposed material and the prospects for using X-ray computed tomography in the matrix source are evaluated.

Correction for ‘A novel concept of two-component dielectric function for gold nanostars: theoretical modelling and experimental verification’ by Nikolai G. Khlebtsov et al., Nanoscale, 2020, 12, 19963–19981, DOI: 10.1039/D0NR02531C.

A mathematical model for the calculation of the optical and thermal properties of an ensemble of gold nanostars with different tip lengths L = 10 to 20 nm in an aqueous environment is proposed. The heating of a nanoparticle ensemble under irradiation by a laser pulse of a nanosecond duration: resonant λ = 808 nm and nonresonant λ = 1064 nm is studied. A significant blue shift of surface plasmon resonance during the formation of a vapor bubble around the nanoparticle was detected and described. Based on the analysis of the kinetics of nanoparticle heating under the action of a laser pulse before and after the formation of a vapor bubble, a theoretical description of the experimentally observed threshold nature of particle photomodification is given. It was found that the laser intensity Im necessary to achieve the melting temperature Tm (photomodification threshold) tends to increase with decreasing nanostar tip length and for an individual nanostar differs by an order of magnitude. However, up to 45% of the nanoparticles are heated to the melting temperature Tm by a single pulse with an intensity only 2.5 times higher than the minimum value of Im. At a wavelength of 1064 nm, Im is ∼6 times higher than at a wavelength of 808 nm.

The tunneling photo effect has been studied in a microdiode with an electrostatic field localized at an emitter based on a nanosized DLC structure. It is established the photocurrent, when the carbon nanoemitter is exposed by laser and tunable low-coherent radiation in the spectral range from UV to near IR with photons of low energy (below work function). A linear dependence of the photocurrent on the level of optical power in the range of micro- and milliwatt power is established. The effect of saturation of the current-voltage characteristics of the tunnel photocurrent associated with a finite concentration of non-equilibrium photoelectrons is observed. The observed spectral Watt-Amper characteristics can be adequately interpreted using a modified Fowler–Nordheim equation for non-equilibrium photoelectrons.

A model for calculating the electrostatic field in the system "probe of a tunnel microscope - a nanostructure based on a DLC film" was developed. A finite-element modeling of the localization of the field was carried out, taking into account the morphological and topological features of the nanostructure. The obtained results and their interpretation contribute to the development of the concepts to the model of tunnel electric transport processes. The possibility for effective usage of the tunneling microscopy methods in the development of new nanophotonic devices is shown.

The paper provides a justification and a comparative analysis of the scaling directions of the developed and investigated planar triode field emission cathode unit with the aim of increasing the maximum field current density up to 0.75 A-cm -2 without sacrificing durability. The design features of the vacuum device with a planar structure provided low-voltage control - at 150 V in the mode of long-term durability and not more than 250 V in the mode of the maximum permissible emission current.

Multiple factors and their impact on the stability of DLC field emission structures are discussed in the present work. Planar multi-electrode structures, in which the formation of zones of localization the electrostatic field of a certain topology performed, are examined. Estimates carried out demonstrated the existence of an effective solution for creating reliable and durable vacuum devices for electronics and photonics. Conclusions are confirmed by the results of experimental studies. Samples of devices showed an average current density of field emission 0.30-0.35 A/cm 2 .

The phenomenon of electron tunnel photoemission from the DLC film structure is discussed. Planar multi-electrode structure provides formation of zones of localization the electrostatic field of a certain topology. Under the influence of a strong electrostatic field, both equilibrium and nonequilibrium (photoexcited or "hot") electrons tunnel into the vacuum from the zone of concentration of electrostatic field. The results of experimental studies and theoretical simulations of the process show the saturation of photoemission current component with an increase in operating voltage. This fact makes it possible to realize the high-speed control of the spectral sensitivity of the photosensor. This is fundamentally important for applications in the modern electronic and photonic devices.

The results of the practical implementation of the concept of field-emission current source with high average current density of 0.1-0.3 A-cm-2 are shown. The durability of cathode samples at a level of 6000 hours is achieved under conditions of technical vacuum. A phenomenological model is suggested that describes the tunneling of both equilibrium and nonequilibrium electrons in a vacuum from the zone of concentration of electrostatic field. Conditions are discussed as the resulting increase in the emission current due to the connection mechanism of the photoelectric effect is thermodynamically favorable, that is not accompanied by an undesirable increase in the temperature of the local emission zone. It is shown that to ensure stability and durability of the cathode is also important to limit the concentration of equilibrium carriers using composite structures «DLC film on Mo substrate." This helps to reduce the criticality of the CVC. A possible alternative is to use a restrictive resistance in the cathode. However, this increases the heat losses and thus decreases assembly efficiency. The results of experimental studies of the structure showing the saturation of photoemission current component with an increase in operating voltage. This fact suggests the existence of an effective mechanism for control of emission at constant operating voltage. This is fundamentally important for the stabilization of field emission cathode, providing a reliability and durability. The single-photon processes and the small thickness DLC films (15-20 nm) provide high-speed process of control.

Gold nanoparticles (AuNPs) of different size and shape are widely used as photosensitizers for cancer diagnostics and plasmonic photothermal (PPT)/photodynamic (PDT) therapy, as nanocarriers for drug delivery and laser-mediated pathogen killing, even the underlying mechanisms of treatment effects remain poorly understood. There is a need in analyzing and improving the ways to increase accumulation of AuNP in tumors and other crucial steps in interaction of AuNPs with laser light and tissues. In this review, we summarize our recent theoretical, experimental, and pre-clinical results on light activated interaction of AuNPs with tissues and cells. Specifically, we discuss a combined PPT/PDT treatment of tumors and killing of pathogen bacteria with gold-based nanocomposites and atomic clusters, cell optoporation, and theoretical simulations of nanoparticle-mediated laser heating of tissues and cells.

The major goal of this study is theoretical analysis and optimization of local laser heating of a medium doped by plasmon-resonant nanoparticles that modeling nanoparticle labeled tissue. We were focused on the development of methods for precise description of optical and thermal processes accounting for their spatio-temporal localization. The results of numerical simulation show that an approach based on using the Arrhenius damage integral provides a more reasonable choice of the size of nanoparticles and exposure modes to provide precise control of hyperthermia with minimal energy consumption.

A mathematical model and numerical simulation of nonstationary temperature field within tissues and cells locally heated under pulse laser irradiation mediated by plasmonic nanoparticles are presented. The essential temperature alterations during laser pulse and time interval between pulses was found. Temperature spatial-temporal profile depends on a number of parameters including optical and thermophysical properties of cell membrane and nanoparticles, laser wavelength, energy, pulse duration and repetition rate. On the basis of introduced parameters a quantitative evaluation of thermal effects was done. The possibilities of usage of these parameters to study their correlation with irreversible photothermal effects, including a change in the permeability of cell membrane during optoporation, are discussed.

The solution of Maxwell-Schrodinger equations describing superradiant scattering of light from a Bose-Einstein condensate of dilute atomic gas is analyzed. A novel method of control the generation of recoil atomic ‘clouds’ and scattered fields by inclined illumination of a Bose-Einstein condensate sample is proposed.

Heating of composite plasmon-resonant nanoparticles (spherical gold nanoshells) under pulse laser illumination is considered. The numerical solution of the time-dependent heat conduction equation accounting for spatial inhomogeneities of absorbed laser radiation is performed. Important features of temperature kinetics and thermal flux inside nanoparticles are analyzed. Possible applications of the observed effects in nanotechnology and medicine are discussed.

Photonic nanotechnologies have good perspectives to be widely used in biophotonics. In this study we have developed an approach for calculation of nanoparticle temperature field accounting for absorbed local intensity at pulse laser radiation of composite spherical nanoparticles (nanoshells). This approach allowed us to analyze spatial inhomogeneities of light field diffracted into a nanoshell and corresponding distribution of the absorption energy and to provide numerical solution of time-dependent heat conduction equation accounting for corresponding spatially inhomogeneous distribution of heating sources. We were able to predict the appearance of a novel thermal effect - hoop-shaped hot zone on the nanoshell surface. The observed effect has potential applications in cell biology and medicine for controlled cell optoporation and nanosurgery, as well as cancer cell killing.

This paper discusses one of the key problems of laser-induced tissue/cell hyperthermia mediated by gold nanoparticles, namely, quantifying and precise prediction of the light exposure to provide a controllable local heating impact on living organisms. The distributions of such parameters as an efficiency factor of absorption, differential and integral absorbing power of a nanoparticle, temperature increment, and Arrhenius damage integral were used to quantify nanoparticle effectiveness in the two-dimensional coordinate space “laser wavelength (λ) × radius of gold nanoparticles (R).” It was found that the fulfillment of required spatial and temporal characteristics of temperature fields in the vicinity of nanoparticle determines the optimal λ and R. As a result, the area in the space (λ × R) with a minimal criticality to alterations of the local hyperthermia may be significantly displaced from the position of the plasmonic resonance. The aspects of generalization of the proposed methodology for the analysis of local hyperthermia using nanoparticles of different shapes (nanoshells, nanorods, nanostars) and short pulse laser radiation are discussed.

Semiclassical theory of cooperative Rayleigh scattering of laser light from Bose-Einstein condensate of dilute gas is considered. The different versions for the process initiation are analyzed.

A semiclassical theory of superradiant scattering of laser light from Bose-Einstein condensate of dilute gases, taking into account the multimode structure of emitted radiation is presented.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The scattering of the extended in time laser pulse from Bose-Einstein condensate of elongated form is considered. The evaluation of the conditions determining the transition from the usual isotropic Rayleigh scattering to the sharply anistropic (directed along the condensate) cooperative or superradiant Rayleigh scattering is presented

Numerical simulation of image formation in near field optical microscopy is needed to understand a relationship between near field images and actual structure of sample since the image can be differs strongly from real structure. In order to estimate the near field image formation, two different approaches are used, namely numerical solution of integral equations with boundary element method or moment method and analytical solution of light scattering problem obtained by assumption of some hypotheses. The first approach results in reasonably complicated algorithm of calculation and often causes a bed conditioned system of linear equations to be formed. The approach based on an analytical solution of scattering problem is more preferable since allow to reduce the algorithm and increase the calculations speed. A new program of simulation of near field image formation for arbitrary sample shape has been developed. The program is based on the results of analytical calculation of near field light diffraction on sinusoidal diffraction grating of arbitrary corrugation amplitude. The sample shape is presented as a number of sinusoidal gratings of various amplitudes by Fourier transformation, for each of the gratings the light scattering amplitude is calculated and the amplitudes are summarized.

The simulation of spontaneous cooperative emission (Dicke superradiance) of initially inverted two-level active centers with the randomly oriented transition dipole moments was performed. The self-organization of the diffraction and polarization structure of radiation (inside the total solid angle) for the thin-sheet sample emission is presented.

The superradiance (SR) of initially inverted two-level active medium in a cavity is considered. We discuss the results specific for the rigorous simulation of the SR pulse (obtained on the basis of 1D Maxwell-Bloch equations solution without slowly varying envelope approximation (SVEA) in the spatial variable): the strong dependencies of the counter-propagating waves correlation and pulse development acceleration not only on the module of the cavity mirrors reflection coefficient, but on the integer- factor of the ratio of the sample length and half of the resonant wavelength. The simple modification of the SVEA model approximately describing the above features is considered.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The superradiance (SR) of a thin layer of inverted two-level active medium has been investigated on the basis ofnumerical solution of semiclassical Maxwell-Bloch equations with stochastic inilial conditions. The correlation ofcounter-propagaling pulses delay limes was analyzed with the account ofdiffraction divergence of radiationKeywords: two-level atoms, Maxwell-Bloch equations, inversion, superradiance, diffraction divergence, correlation 1. INTRODUCTION One of the important features of the solid state SR (observed in the experimental invesligations') is the appearance of correlations between the pulses propagaling in the counter directions along the extended prolonged sample. The corresponding theoretical treatments have been performed2 8 There was noted the following feature ofthe SR pulse athigh concenlmlion ofinitial inversion7' 8: There is a strong dependence ofthe counter-pulses correlation on the X/4 (X - is the resonant wavelength) repetition limesin the sample length L. IfL is halfinteger-multiple ofA./2, there is a maximum ofcorrelation and vice versa when L isinteger multiple of?J2. However, the above treatments2 8

We consider a pencil-shaped active medium consisting of two- level initially excited atoms and described by 1D Maxwell- Bloch equations. With the help of these equations solution without slowly varying envelope approximation we shown, that internal field reflections from the ends of the sample transform the so-called 'lethargic' regime of super-radiance (SR) pulse amplification to the amplification regime similar to usual exponential law. iT can lead to the pulse development acceleration and counter-propagating waves synchronization. A simple formula for SR pulse delay time evaluation is presented. The criterion of the counter- propagating waves synchronization is discussed.

The spontaneous cooperative emission (superradiance) of initially excited two-level active centers (atoms) inside Fabry-Perot resonator was considered. With the help of numerical solution of coupled Maxwell-Bloch equations the kinetics of atomic system and output field evolution were obtained. The strong dependencies of the superradiance pulse parameters on the resonator characteristics were analyzed.

Spontaneous cooperative emission of the pencil-shaped sample was simulated on the basis of Maxwell-Bloch equations without approximation of slowly varying (in space) amplitudes of the electric field and medium polarization. Using the numerical and derived approximate analytical solution of these equations the influence of the internal field multiple reflections (from the sample ends) on the pulse parameters was analyzed. The counter-propagating waves synchronization and pulse development acceleration are discussed.

The dynamics of spontaneous cooperative emission in a cavity was investigated by numerical solution of semiclassical Maxwell-Bloch equations without slowly varying envelope approximation (in spatial variable). The dependencies of the pulse parameters on the resonator characteristics under condition of high phase relaxation of active medium are discussed.

The simulation of superfluorescence of a thin layer of two-level atoms was performed on the basis of semiclassical approach without using approximation of slowly varying in space amplitudes of electric field and medium polarization (paraxial approximation). The evolution of atomic characteristics and the structure of the radiation directivity pattern inside the total solid angle have been investigated. The comparison of the results obtained with the results based on the paraxial approximation has been done.

Using the semiclassical approach the simulation of the light pulse generation by a thin layer of quantum two-level dipoles has been performed. The state of each dipole is governed by Bloch equations for individual density matrix elements under condition of phase relaxation absence. Identical dipoles are located at the nodes of 2-D grating with corresponding sizes Lx, Ly and are considered as pointlike sources of classical field. At the initial moment all the dipoles are in an inverted state Initiation of the pulse was carried out by either incoherent spontaneous decay (superfluorescence mode simulated by setting of small random polarisation with *-correlation) or coherent initial state. Based on the numerical solution the kinetics of dipoles characteristics and evolution of the radiation directivity pattern have been calculated. The influence of the initial state and short-range Coulomb dipole-dipole interaction on the pulse characteristics have been analysed. Tending of axis X to be a direction of primary amplification of pulse with increasing of inequality Lx > Ly has been traced. The comparison of the results obtained with the results of paraxial approximation that uses the concept of slowly varying along axis X amplitudes of the electric field and medium polarisation has been done.

A new testing method of the surface roughness is discussed. The method is based on the usage of the probing laser beam with spatial modulation in the form of a regular interference pattern, and of the contrast change effect of the patter in the scattered light depending on the tested surface roughness parameters. The method theory based on the interference of the identical speckle modulated waves formed in the diffraction field is presented. This method permits us to determine phase inhomogeneities standard deviation, correlation length and object phase inhomogeneities form of the correlation coefficient. Experimental results of the phase inhomogeneities of television screens and phase specklegrams testing are presented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A new testing method of the surface roughness of transparent and reflecting objects is discussed. The method is based on the usage of the probing laser beam with spatial modulation in the form of a regular interference pattern, and of the contrast change effect of the pattern in the scattered light depending on the tested surface roughness parameters. A theory of the technique is presented. Various types of devices for the dynamic interference field formation in the probing laser beam (on the basis of interferometers, acoustic-optical modulators, optical and holographic elements with a piezoelectric deflector) are considered. A specialized processor of dynamic interference signals has been used to convert the measured contrast values. The experimental results of surface roughness testing of television screens are presented. The possibility of the technique usage in small angle scattering investigations is discussed. Consideration is also given to the feasibility of the technique industrial application in the rapid testing of the products surface quality while in production.

We present a new design method for Dammann gratings that is based on design theory for diffractive ele- ments. It allows the calculation of binary as well as multilevel phase structures in one and two dimensions. These phase structures are optimized in diffraction efficiency and uniformity.

The authors discuss the problem of polarized laser beam diffraction on extended rough plates with a regular structure. Using the method of equivalent sources, they arrive at the simple approximate formulae for Muller matrix elements valid for wide beams scattered by the samples with small periodic profile surfaces. For the calculation of other parameters, the widely known algorithms for the plane electromagnetic wave diffraction on the unlimitedly extended rough plates of the same structure are used.