Frequency Of Incident Light Research Articles

Super-resolution and frequency-dependent efficiency of near-field optical disks with silver nanoparticles

The super-resolution capability of the AgOx-type super-resolution near-field structure disk with silver nanoparticles was studied using finite-difference time-domain method at different incident light frequencies. The near fields exhibited strongly local field enhancement around silver nanoparticles in the AgOx layer due to localized surface plasmon. The subwavelength recording marks smaller than lambda/10 were distinguishable since the metallic nanoparticles with high localized fields transferred evanescent waves to detectable signals in the far field. The far-field signals from random silver nanoparticles displayed similar behaviors as those from single nanoparticle and red-shifts of peak frequencies from particle-particle interaction.

Quantum size-dependent third-order nonlinear optical susceptibility in semiconductor quantum dots

The density matrix approach has been employed to investigate the optical nonlinear polarization in a single semiconductor quantum dot(QD). Electron states are considered to be confined within a quantum dot with infinite potential barriers. It is shown, by numerical calculation, that the third-order nonlinear optical susceptibilities for a typical Si quantum dot is dependent on the quantum size of the quantum dot and the frequency of incident light.

Estimation of a Brillouin power spectrum distribution based on an iterative weighted least mean square method

AbstractA fiberoptic strain sensor is being developed that exploits the fact that the difference between the central frequency of Brillouin scattering, which is a type of back scattering that occurs in optical fibers, and the incident light frequency depends on the strain of the optical fiber. The measurement of the central frequency of the Brillouin scattering requires an estimation of the power spectrum distribution of the Brillouin scattering. An improvement in distribution estimation accuracy can potentially improve both the accuracy of central frequency measurements and the precision of strain measurements. Focusing on the problem of the power spectrum distribution of the Brillouin scattering, this paper proposes a weighted repetition least mean square algorithm. The paper also examines the stability of the proposed repetition algorithm and demonstrates the effectiveness of the proposed approach through simulations. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(1): 72–80, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1183

Finite Element Analysis of Optical Bistability in One-Dimensional Nonlinear Photonic Band Gap Structures with a Defect

We present a new approach based on the recently reported finite element scheme16 to study the optical response of a finite one-dimensional nonlinear grating. Using the transmitted wave amplitude as a numerical input parameter, we are able to find all stable and unstable solutions related to a specific incident wave which build up the complete bistability curve. The method is applied to investigate the optical bistability in a nonlinear quarter-wave reflector with a defect. With a proper choice of the incident light frequency, a very low bistability threshold is predicted for an optimized defect structure.

A method for determining thickness and optical constants of absorbing thin films

In this paper, we present a method for determining the refractive index, extinction coefficient, and thickness of thin films using reflectance and transmittance measurements for one frequency of incident light. The measurement of reflectance is conducted from both sides of the sample and transmittance from either one of the two sides. All measurements are conducted at the same angle of incidence with either s- or p-polarized light. The usual assumptions about the sample (substrate with deposited thin film) are made: (1) homogeneity of the deposited thin film; (2) uniform film thickness over the measurement area; (3) non-absorbing incoherent substrate; (4) the film is absorbing, i.e. the extinction coefficient is not 0. A computer program to solve the three equations, two equations for reflectance and one equation for transmittance, to determine the refractive index, extinction coefficient, and thickness of thin film has been developed and tested on simulated data.

An extensive study of the photocurrent amplification mechanism of silicon bulk-barrier diodes based on simulation and experimental results

In this paper, an extensive study of the photocurrent amplification mechanism of silicon bulk-barrier diodes (BBDs) is presented, based on simulation and experimental results. As a result of this study an analytical model is proposed. The proposed model extends previously published models and includes analytical expressions for all significant quantities of the device optoelectronic behaviour. Such quantities are barrier lowering, photocurrent, quantum efficiency and response speed as functions of the applied voltage, incident light power, light wavelength and modulation frequency, as well as a function of technological parameters. Simulation and experimental results verify the validity of the proposed analytical model, and they show that BBDs are majority carrier photodetectors with high internal photocurrent gain. Compared with common photodetectors, BBDs exhibit a very high sensitivity in the blue region of the visible spectrum.

Finite-difference time-domain analysis of optical bistability with low threshold in one-dimensional nonlinear photonic crystal with Kerr medium

We present a nonlinear finite-difference time-domain (NFDTD) analysis of optical bistability (OB) in a one-dimensional nonlinear photonic crystal (1D-NPC) with Kerr medium under Debye relaxation. The properties of the defect modes in a symmetrical structure 1D-NPC and the way to obtain low threshold of OB is discussed in detail. The OB threshold depends on the optical thickness and refractive index of defect layer and the number of symmetrical layers. When the half-width of defect mode is small enough and frequency of incident light and linear refractive index are selected carefully, the low threshold OB is able to be obtained. By numerical simulation threshold ∼ 130 KW/ m 2 is obtained, correspond refractive index change is only about 0.04.

Enhancement of phase-coherent electromagnetic scattering from a random array of identical resonant dielectric ridges placed upon a dielectric substrate

The elastic scattering of p-polarized electromagnetic waves from a one-dimensionally rough surface formed as an array of identical resonant dielectric ridges randomly placed upon a dielectric substrate is studied as a function of the frequency of incident light. A diagrammatic perturbation theory is used. Emphasis is given to determining how the resonant properties, as a function of frequency, of the dielectric ridges affect phase-coherent (weak-localization) phenomena in electromagnetic scattering by the surface and how these effects are related to localized electromagnetic modes bound to individual ridges.

Second Harmonic Generation from Mixed Films of Rhodamine Dye and Arachidic Acid at the Air−Water Interface: Correlation with Spectroscopic Properties

Mixed insoluble monolayers of bis(N-ethyl,N-octadecyl)rhodamine perchlorate (RhC18) and arachidic acid (ArAc) at the air−water interface were characterized by surface pressure−area isotherm, second harmonic generation (SHG), and reflection spectroscopy studies. The analysis of surface pressure−area isotherms of mixed RhC18/ArAc layers provided evidence that there was a high degree of miscibility of film components and a strong interaction among them. A new band was found to appear on the blue side of the reflection spectrum after an increase in both the concentration of ArAc in the layer and the applied surface pressure. This new band was assigned to dye aggregates, where spontaneous formation in the gaslike region was promoted by the presence of ArAc and induced by compression in the region of the continuous monolayer. Both in gaslike and in compressed film, the formation of blue-shifted aggregates coincided with the increase of the SHG response of the monolayer. Resonance SHG enhancement was proven to be the main reason for this observation due to electronic resonance of aggregates with the incident light frequency.

Depth profiling of strain using micro-Ramanmeasurements

We describe a method to determine the variationof strain with depth in a sample using Raman measurements. Themethod involves recording Raman spectra using incident lighthaving different absorption coefficients. These can beobtained using a single incident light frequency by adjustmentof the point of focus. The Raman spectra are then processedusing a Laplace transform to obtain the characteristic elasticstrain as a function of depth. The method is illustrated usingseveral model strain distributions. It is applicable topractical cases such as graded interfaces and strained/relaxedepitaxial layers.

Green function method and its application to the resonance Raman effect

AbstractThe advantages of the Green function method for considerations in resonant Raman scattering are shown. It is possible to avoid difficulties which arise when the frequency of incident light is in the excitonic absorption band. Copyright © 2001 John Wiley & Sons, Ltd.

Magnetooptical properties of Fe/Pd multilayer films

Multilayer films of Fe(x)/Pd(30 A) (6≤x≤30 A) are investigated with the help of the transversal Kerr effect (TKE) with incident light in the energy range 1.3–3.6 eV. Oscillations of the TKE depending on the thickness of the iron layer are revealed. The off-diagonal element of the dielectric tensor ɛ 2 ′ is calculated using themeasured values of the TKE for two incidence angles of light and the optical constants of all samples. It is shown that the quantity ɛ 2 ′ ω2 (where ω is the frequency of incident light), which is proportional to the interband density of states, also oscillates, and its oscillations are similar in character to oscillations of the Kerr effect. The observed oscillatory dependence of the TKE and of the interband density of states are related to the manifestation of quantum confinement effects.

Multichannel conical emission and parametric and nonparametric nonlinear optical processes in ytterbium vapor

Collimated and conical emissions that appear when Yb vapor is illuminated by light pulses at 262 nm (near the one-photon Yb 6s2 1S0→6s7p 3P1 transition) are experimentally investigated. Conical emission is observed at multiple wavelengths. Parametric and nonparametric nonlinear optical processes are studied by investigation of the spatial distribution of generated light and the efficiency of light generation as a function of the incident light frequency.

Nonlinear Optical Response of a Fibonacci Multilayer

By studying numerically the light transmitting through a finite nonlinear Fibonacci multilayer, we find the gap-soliton-like phenomenon. The Fibonacci multilayer contains a Kerrtype nonlinearity in one component. When the frequency of incident light is in a stop gap, increasing the incident light intensity will make the system switch from a lower transmission state to a higher transmission state. Transmissivity for some frequencies can reach unit, which shows that they correspond to transparent states. Distribution of the field intensity in the Fibonacci structure has a particular gap-soliton-like shape, which has the multi-carrier wave.

Resonance tunneling through photonic quantum wells

The band gap in photonic materials with periodic spatial modulation of refractive index greater than unity can actually be regarded as a potential barrier for photons. Similar to semiconductor quantum well systems due to the electronic band-gap mismatch, a photonic quantum well can be constructed by sandwiching a uniform medium between two photonic barriers. The transmission and reflection coefficients of light through the photonic quantum well are calculated by a modal expansion method with an R-matrix propagation algorithm. Resonance tunneling through the photonic quantum well structure is observed by varying either the well width or the frequency of incident light. Resonance peaks are found within the band-gap region, and indicate the existence of photon virtual states in the well.

Dynamic theory of two-photon correlators in the spectroscopy of single impurity centers

A dynamic theory of two-photon correlators measured in experiments with single molecular impurity centers has been developed. The theory takes into account the interaction between optically active electrons of an impurity center and phonons, excitations in tunneling systems of polymers and glasses, and transverse electromagnetic field. Both the correlator measured in the start-stop regime and the “full” correlator have been analyzed, and equations for these correlators have been derived. An equation relating these two correlators has been also obtained. The effect of the triplet level of an impurity molecule on the correlators leading to bunching of spontaneously emitted photons has been studied. The two-photon correlators have been calculated numerically, and their dependence on the incident light frequency and time between the pairs of detected photons in various realistic situations has been derived.

Electronic Stark Effect Studies of a Porphyrin-Based Push−Pull Chromophore Displaying a Large First Hyperpolarizability: State-Specific Contributions to β

Electroabsorption or Stark effect spectroscopy has been applied to a pair of porphyrin-based chromophores with the aim of deriving a detailed understanding of the origin of the remarkable first hyperpolarizability, β, of one of the chromophores: [5-[[4‘-(dimethylamino)phenyl]ethynyl]-15-[(4‘‘-nitrophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II). The measurements show that significant changes in molecular dipole moment, Δμ, accompany excitations of x-polarized transitions of the aminophenyl (donor)/nitrophenyl (acceptor) functionalized chromophore, but are absent for a related chromophore lacking the donor and acceptor groups. For linear chromophores, changes in dipole moment are a prerequisite to effective molecular first hyperpolarization and incident light frequency doubling behavior. A more detailed consideration of the available |Δμ| data, within the context of a conventional two-level model, has yielded the following: (a) specific information about the roles of each of seven electronic and vibron...

Dependence of the Daman intensities of combinations and overtones on the frequency of incident light

is shown that the combined method for calculating the Raman tensor elements suggested earlier [1, 2] may be extended to calculations of the intensities of second-order Raman bands (overtones and combinations). The behavior of the intensities of the first- and second-order Raman bands is studied in a wide range of frequencies of incident light, including the resonance region. The resulting equations for the Raman scattering tensor elements are convenient from computational viewpoint; this is especially important for the intermediate frequencies, which are most difficult for calculations.

The influence of quasi-localized carrier states on the optical properties of size-quantizing structures

We considered the optical properties of size-quantizing semiconductor structures with quasi-localized electron states. In particular, the formulae we obtained allow us to determine the optical absorption due to electron transitions from the localized ground state to an excited quasi-localized (resonant) one. The calculations were carried out for objects of various dimensionalities, that is for a layered structure (quantum well) and a spherically symmetric irregularity (quantum dot), suggesting a certain model potential. The obtained results qualitatively correspond to the experimental observations, yielding an intermediate picture, when compared to the electronic transitions to an excited bound state and to a delocalized band state. Having derived a formula for the absorption cross-section of a single quantum well, we also obtained expressions for the corresponding corrections to the absorption coefficient, refractive index and dielectric constant of the multi-quantum well structure as functions of the frequency of incident light and the parameters of the quantum wells and barriers. The results may be useful in designing quantum well infrared photodetectors.

Absorptive bistability in a dielectric sphere

Theoretical results on absorptive optical bistability of micron-sized droplets doped with a saturable absorber are presented. Bistability is observed only when the incident light frequency is near or on a morphology dependent resonance of the sphere. Results on Q-switching are also presented.