Effect Of Resonant Excitation Research Articles

Electromagnetic wave passage through impedance-matched graded interfaces between RHM and LHM media: passive and active transition layer variants.

We suggest two new, to the best of our knowledge, models of a flat-layered medium with variable electric permittivity and magnetic permeability. They represent a smooth transition from an ordinary medium with positive parameters to a medium with negative ones. An analytical solution to the problem of transition of a plane electromagnetic wave through such media, which describes the phenomenon of negative refraction is obtained. The resonant excitation effect is observed in the case of the medium with an active transition layer.

Molecular and plasmonic resonances on tip-enhanced Raman spectroscopy

Plasmon has been widely investigated and applied, because it can greatly enhance molecular Raman spectral intensity. In this study, the resonance Raman effect of the tetra-tert-butylnaphthalocyanine (TTBN) is analyzed, including the Raman wave number shift and enhancement factor, resulting from light of different incident wavelengths. Furthermore, the optical properties of TTBN are obtained, such as charge transfer, the electronic circular dichroism (ECD) spectrum, etc. Lastly, we study the tip-enhanced Raman spectroscopy (TERS) by adjusting the parameters of the metal tip to achieve the highest electromagnetic enhancement at different incident wavelengths. Combining the resonance excitation effect and the tip enhanced Raman effect, the enhancement factor of TERS can reach up to 108–109. This study provides significant help for a profound understanding of the TERS mechanism.

Charge transfer and electromagnetic enhancement processes revealed in the SERS and TERS of a CoPc thin film

Abstract Phthalocyanines are frequently used as probing molecules in the field of single-molecule surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). In this work, we systematically compare the SERS and TERS spectra from a thin cobalt phthalocyanine (CoPc) film that is deposited on a Au film. The contributions from electromagnetic (EM), resonance, and charge-transfer enhancements are discussed. Radially and azimuthally polarized vector beams are used to investigate the influences of molecular orientation and the localized surface plasmon resonance (SPR). Furthermore, two different excitation wavelengths (636 and 532 nm) are used to study the resonant excitation effect as well as the involvement of the charge-transfer processes between CoPc and the Au substrate. It is shown that the Raman peaks of CoPc are mostly enhanced by 636 nm excitation through a combination of resonant excitation, high EM enhancement, and chemical enhancement via charge transfer from the metal to the molecule. At 532 nm excitation, however, the SERS and TERS spectra are dominated by photoluminescence, which originates from a photo-induced charge-transfer process from the optically excited molecule to the metal. The contributions of the different enhancement mechanisms explain the optical contrasts seen in the TERS images of Au nanodisks covered by the CoPc film. The insight achieved in this work will help to understand the optical contrast in sub- or single-molecule TERS imaging and apply SERS or TERS in the field of photocatalysis.

Resonant Excitation of Baroclinic Waves in the Presence of Ekman Friction

The quasi-geostrophic dynamics of disturbances of a flow with a vertical shear is described by a transfer equation for potential vorticity. Wave solutions of this equation are represented by edge baroclinic waves (modes in a discrete spectrum) and singular modes in a continuous spectrum. When frequencies of these modes coincide, the effect of resonant excitation occurs in which the amplitude of baroclinic waves increases linearly. This paper studies this effect in the presence of Ekman bottom friction. It is shown that friction suppresses linear wave growth and gives rise to baroclinic waves of finite amplitude.

Absolute vibrational cross sections for low energy electron (1-19 eV) scattering from condensed tetrahydrofuran (THF)

SynopsisAbsolute cross sections (CSs) for vibrational excitation were obtained for low energy electron impact with tetrahydrofuran (THF) molecules condensed on Ar at 19K. The absolute CSs were measured with a high resolution electron energy loss spectrometer for the 1 to 19 eV incident electron energy range. The values of the vibrational CSs are found to lie within the 10-17cm2 range and to show the effects of resonant excitation.

Analytical approach and reconstruction of the density matrix of coupled oscillators

We present an analytical approach to solve the wave function and reconstruct the density matrix for a linear x–x coupled oscillator system. The method is available both for weak and strong coupling systems. Employing our method, we analyse the probability distribution function, dynamical recurrence and non-Gaussian entanglement. Including the dissipation, we reconstruct the density matrix in the Liouville-space. Supplying both analytical and numerical treatment, we obtain the steady-state solution of the density matrix and discuss the effect of resonant excitation.

Effects of resonant excitation, pulse duration and intensity on photoelectron imaging of a dianion

The photoelectron imaging of the indigo carmine dianion is used to demonstrate the effects of resonance excitation, pulse duration and pulse intensity on the photoelectron spectra and angular distributions of a dianion. Excitation of the S1 state leads to an aligned distribution of excited state dianions. The photoelectron angular distribution following subsequent photodetachment within a femtosecond laser pulse is primarily determined by the repulsive Coulomb barrier. Extending the timescale for photodetachment to nanoseconds leads to dramatic changes in both the spectral and angular distributions. These observations are explained in terms of statistical detachment of electrons, either from the monoanion, or from the ground state of the dianion following a number of photon cycles through the S1 ← S0 transition. At high intensity, new electron emission channels open up, leading to emission below the repulsive Coulomb barrier. This has been assigned to strong-field induced detachment and the effect of an electric field on the Coulomb barrier is discussed in terms of the photoelectron spectra and angular distributions.

Experimental research on the spectral response of tips for tip-enhanced Raman spectroscopy

Based on unilateral total internal reflection illumination, a tip spectral response detection setup is built. This provides an experimental method for revealing the spectral response and resonance band, which are significant in investigating optical properties and the field enhancing mechanism. The spectral responses of silicon tips coated with gold and silver are detected. These tips are then used in tip-enhanced Raman spectroscopy (TERS) detection under 532 nm excitation to demonstrate the effect of resonant excitation on field enhancement. The corresponding relationship between the measured spectral response and the tip’s enhancement performance in TERS is discussed.

Plasmon-Based Optical Trapping of Polymer Nano-Spheres as Explored by Confocal Fluorescence Microspectroscopy: A Possible Mechanism of a Resonant Excitation Effect

Plasmon-Based Optical Trapping of Polymer Nano-Spheres as Explored by Confocal Fluorescence Microspectroscopy: A Possible Mechanism of a Resonant Excitation Effect

Plasmon-Based Optical Trapping of Polymer Nano-Spheres as Explored by Confocal Fluorescence Microspectroscopy: A Possible Mechanism of a Resonant Excitation Effect

In optical trapping using photon force much enhanced by localized surface plasmon (LSP) in solution, we found that a resonant excitation effect can further enhance photon force. In this LSP-based optical trapping under a resonant excitation condition, an incident laser beam excites both LSP and electronic resonant transition of a target object simultaneously. Fluorescence microspectroscopy clearly showed that nanospheres under the resonant condition were much more efficiently trapped as compared to that under a non-resonant condition. The resonant LSP-based trapping mechanism was further reinforced by theoretical calculations taking the resonant excitation effect into account. Such resonant LSP-based trapping methodology will provide a novel approach for efficient trapping of small molecules.

Research on light-wave target detection and imaging by using NR-PC flat lens with active impurities

The authors mainly use the two-dimensional finite-difference time-domain method to study the effection on image resolution of target detection and imaging when active impurities are introduced to negative refraction photonic crystals (NR-PC) flat lens. It is demonstrated that because of the influence of the mini-forbidden band and resonance excitation effect, high transmissivity will appear at the resonance frequency of 0.3068(a/λ) when the light wave goes through the NP-PC lens. Also, the results show that the refocused wave backscattered from a target is significantly stronger than the directly backscattered wave when no NR-PC flat lens is applied. Further studies demonstrated that the introduction of active impurities into NR-PC lens provides improved refocusing and image resolution. In conclusion, the authors' investigation optimises the performance of the focus-scanning scheme, and provides the basis for converting an idealised left-handed materials (LHM) lens into a physically realisable NR-PC flat lens.

Two-square target detection and imaging using NR-PC flat lens

The characteristics of two-target detection and imaging from negative-refraction photonic crystal (NR-PC) flat lens are studied by using the two-dimensional finite-difference time-domain method. It is demonstrated that due to the influence of the mini-forbidden band and resonance excitation effect, high transmissivity will appear at the normalized resonance frequency of 0.3068 when the lightwave goes through the NR-PC lens. Meanwhile, the use of the NR-PC lens may introduce at least fourfold improvement of the refocusing resolution, if compared to the directly backscattered lightwave without using the NR-PC lens. In addition, by giving a defination for two-target minimum distinguishable distance, we further investigate the performance of two-target detection and imaging system using the proposed focus-scanning scheme. The results show that the smaller the size of the target pair is, the weeker the interference between the two targets will be, which results in a better performance in the minimum distinguishable distance.

Resonant excitation of evanescent spatial harmonics in medium formed by parallel metallic nanorods

The results of analytical modeling of the resonant excitation of evanescent harmonics in a medium formed by parallel metallic nanorods taking into account the spatial dispersion are presented. Analytical expressions are derived for the reflection and transmission coefficients, as well as for the amplitudes of electromagnetic waves inside the medium. These expressions are compared to similar expressions that were previously obtained using a local model of an ultimately anisotropic material without taking into account the spatial dispersion. The obtained expressions are simplified for various partial cases, including the superresolution imaging of a source that is located at a considerable distance from the metamaterial layer. A layer of a medium composed from finitesized wires is numerically simulated and it is demonstrated that, due to the effect of resonant excitation of evanescent spatial harmonics in the layer, subwavelength details of an object that is considerably distant from the layer can be distinguished inside of the layer.

The application of dynamic scanning in target detection and imaging based on an NR-PC flat lens

In this paper a finite-difference time-domain method is used to model and analyze the application of dynamic scanning in target detection and imaging by using an effective negative-refraction photonic crystal (NR-PC) flat lens. The results show that there is a transmission peak, with a value far greater than unity, resulting from the influence of mini-forbidden bands and resonance excitation effect at a resonance frequency of 0.3068(a/λ). Thus, the lightwave emitted from the point source will provide strong backscattered waves after being focused on the target by the NR-PC lens that greatly improves the refocusing resolution and imaging resolution of the backscattered wave. Furthermore, a comparison with a non-dynamic scanning scheme clearly demonstrates that the dynamic scanning scheme provides improved refocusing resolution. In conclusion, our investigation optimized the performance of a detection and imaging system, and provided the basis for converting an idealized LHM lens into a physically realizable NR-PC flat lens.

Application of photonic crystal enhanced fluorescence to cancer biomarker microarrays.

We report on the use of photonic crystal surfaces as a high-sensitivity platform for detection of a panel of cancer biomarkers in a protein microarray format. The photonic crystal surface is designed to provide an optical resonance at the excitation wavelength of cyanine-5 (Cy5), thus providing an increase in fluorescent intensity for Cy5-labeled analytes measured with a confocal microarray scanner, compared to a glass surface. The sandwich enzyme-linked immunosorbent assay (ELISA) is undertaken on a microarray platform to undertake a simultaneous, multiplex analysis of 24 antigens on a single chip. Our results show that the resonant excitation effect increases the signal-to-noise ratio by 3.8- to 6.6-fold, resulting in a decrease in detection limits of 6-89%, with the exact enhancement dependent upon the antibody-antigen interaction. Dose-response characterization of the photonic crystal antibody microarrays shows the capability to detect common cancer biomarkers in the <2 pg/mL concentration range within a mixed sample.

Numerical research on properties of optical-wave target detection and imaging from NR-PC flat lens

The characteristics of optical-wave target detection and imaging from a negative-refraction photonic crystal (NR-PC) flat lens are studied with a two-dimensional (2D) finite-difference time-domain (FDTD) method in the paper. The results show that there exists a transmission peak, with a value far greater than unit, resulting from the influence of the mini-forbidden bands and resonance excitation effect at resonance frequency. Also, the refocusing of backscattered optical wave from the target leads to its image with a sub-wavelength lateral resolution and great amplitude as long as the target is placed at the focus of the NR-PC flat lens. Therefore, the NR-PC flat lens will find many implications in optical area, especially in the detection and imaging of small targets.

Image resolution and the properties of optical-wave target detection and imaging by using the NR-PC flat lens

We used the method of two-dimensional (2D) finite-difference time-domain (FDTD) to study the characteristics of optical-wave target detection and imaging from negative-refraction photonic crystal (NR-PC) flat lens in the paper. The theory of image resolution was introduced. The results show that there exists a transmission peak, with a value far greater than unit, resulting from the influence of the mini-forbidden bands and resonance excitation effect at resonance frequency. And, the refocusing of backscattered optical wave from the target leads to its image with a sub-wavelength lateral resolution and great amplitude as long as the target is placed at the focus of the NR-PC flat lens. And the application of NR-PC flat lens can be extended in optical area, especially in the detection and imaging of small target.

Effect of gas flow on the growth of In-rich AlInN films by metal-organic chemical vapor deposition

Indium-rich AlInN are grown by metal-organic (MO) chemical vapor deposition using trimethylaluminum, trimethylindium, and ammonia. Under the conservation of MO influx, the effects of gas flow in the MO route on AlInN growth and Al-related parasitic reaction are investigated. With an increase in this gas flow, the suppression of Al-related parasitic reaction, i.e., enhancement in Al content incorporation and improvement of crystalline quality, is satisfactorily shown until the occurring of severe phase separation. Accordingly, Al content x in AlxIn1−xN can be tuned from x=0.02 to 0.26. The Raman spectra of those AlInN samples with phase separation are analyzed by the resonant excitation effect and two-mode behavior for A1(LO). Finally, we propose a phase diagram to interpret the phase separation and Al content evolution under the influence of gas flow.

Free electron laser induced forward transfer method of biomaterial for marking

AbstractBiomaterial, such as chitosan and poly lactic acid, containing a fluorescence agent was deposited onto biologic hard tissue, such as teeth, the claws of dogs or cats, or a sapphire substrate by free electron laser induced forward transfer method for direct write marking. Spin‐coated biomaterial with the fluorescence agent Rhodamin 6G or zinc phthalocyanine target on a sapphire plate was ablated by a free electron laser (resonance absorption wavelength of biomaterial: 3380 nm). In particular, the influence of the spin‐coating film‐forming temperature on hardness and adhesion strength of the biomaterial is studied. The effect of resonance excitation of the biomaterial target by turning the free electron laser is discussed with respect to damage in terms of biomaterial, rhodamin‐6G, or zinc phthalocyanine for direct write marking. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(4): 60–66, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20795

Resonance excitation effect for a molecule driven by a laser radiation field: Algebraic dynamics method to determine the diabatic energy levels and geometric phase

Using the method of algebraic dynamics, we investigate the h omega(4) non-autonomous quantum system, which is formed by a single molecule within a harmonic potential driven by laser radiation field and obtain the exact solutions of the system. Based on the exact solutions, in particular on the features of the diabatic energy levels, then we proceed to studying the geometric phase of the system. From the above results, we may determine the vibration frequency of the molecule by measuring the changes in the properties of geometric phase. (C) 2007 Elsevier B.V. All rights reserved.