Enhancement of Raman scattering by individual dielectric microspheres

Enhanced Raman scattering (ERS) from bulk Si and surface brilliant cresyl blue (Bcb) molecules was investigated by individual polystyrene (PS) microspheres placed on top of the samples. It is revealed that the Raman signal depends both on the microsphere size and the numerical aperture (NA) of the collection lens, and a maximum signal enhancement of ∼11‐ and 40‐fold for Si and Bcb is observed, respectively, showing strong ERS effect. The different ERS behavior was elucidated by electromagnetic simulations using the finite element method. The present work also provides information on individual dielectric sphere for applications in microscopy, spectroscopic imaging and improvement, etc. Copyright © 2010 John Wiley & Sons, Ltd.     

Enhancement of Raman scattering intensity in porous silicon

An enhancement in inelastic light scattering intensity from porous-silicon quantum wires has been discovered. It is shown that this effect is caused by a decrease in the absorption coefficient of the optical medium formed by quasi-one-dimensional structures, with the crystal structure of the wires themselves remaining unchanged. Fiz. Tverd. Tela (St. Petersburg) 41, 1320–1322 (July 1999)     

Enhancement of Raman scattering by parametric mixing of the pump with its harmonic

A strong focusing of the pump laser is generally used to reduce the Stimulated Raman Scattering (SRS) threshold, but it also produces a phase matching condition in the region of strong gain. This causes a large threshold for SRS in the near infrared due both to the increased diffraction limit and to the destructive interaction of antiStokes–Stokes processes. However the phase matching condition can be used to reduce the threshold by Raman parametric mixing (RPM) of the pump with the second harmonic generated by a fraction of pump. It this way we have observed a lowering of the threshold of about a factor 2.3 and an increase of the SRS of the pump.     

Enhancement of Raman scattering of light by ultramarine microcrystals in presence of silver nanoparticles

Approximately 10²‐fold enhancement of Raman scattering by ultramarine microcrystals is reported by means of interaction with silver nanoparticles in films and powders. Theoretical modeling predicts the maximal 10¹⁰‐fold enhancement in close vicinity of a silver spherical nanoparticle (0.24 nm) with rapid decay of enhancement factor to 1 in the range of approximately 50 nm. Experimental enhancement factor is treated as overall effect within the small portion of every microcrystal in the close vicinity of silver nanoparticle(s). The results are considered as an important extension of traditional surface enhanced molecular Raman spectroscopy towards bigger inorganic probes. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman scattering by silicon

Reflection Raman spectroscopy has been performed on silicon at room temperature. One-phonon fine structure, which has been predicted by Cowley and observed in part by Wright et al., is fully obtained. Two-phonon structure is also obtained, which includes the most intense broad band observed by Parker et al. and weak broad bands not observed by them. One- and two-phonon structures reported here are very similar in shape to the ones predicted by Cowley by considering the anharmonicity of the lattice forces.     

表面极化声子的喇曼散射研究

本文主要研究表面极化声子的喇曼散射.在探测表面极化声子的衰减全反射方法以及喇曼散射方法的基础上,借鉴了Kretchmann配置的衰减全反射喇曼散射法,提出了Otto配置的衰减全反射喇曼散射法,并以CaF_2单晶体为样品做了一系列实验.同时,本文利用了能量守恒及平行于样品表面的能量守恒关系,利用了格林函数或响应函数所推出的表面极化声子的一般频散关系,理论上给出了CaF_2-空气表面极化声子的一个唯象的频散关系.实验上用特定设计制做的一个样品架对CaF_2样品测定了它与空气界面上的表面极化声子的频散关系,比较结果,理论与实验取得了比较令人满意的一致.     

Enhancement of Raman scattering by ultramarine using silver films on surface of germanium quantum dots on silicon

The germanium on silicon (Ge-on-Si) semiconductor nanostructures with a vacuum-deposited silver coating are tested as substrates for detecting microamounts of inorganic crystalline ultramarine pigment by enhanced Raman scattering (SERS). At least tenfold enhancement of Raman lines is obtained. The quantum-chemical calculations are performed and used to assign the bands in the Raman spectra. A significant electrooptic anharmonicity of vibrations of chromophore groups in the presence of an SERS-active compound is found.     

Enhancement of different-order Stokes waves of simulated Raman scattering by using a mixed-dye solution in different proportions

A new laser tuning method of enhancing the different orders of Stokes waves by using mixed-dye fluorescence is reported. The Stokes waves from the second order to the fifth order of CCl₄ are enhanced by the fluorescence of mixed R6G and RB alcohol solutions in different proportions, respectively. It is also reported that the first-order, second-order, and third-order Stokes waves of benzene are enhanced by the fluorescence of mixed solutions of R6G and DCM in different proportions. The enhancing mechanism is also discussed.     

Raman scattering enhancement by dielectric spheres

Raman scattering experiments were performed on Si(60 nm)/metal/substrate structures with and without silica microspheres (with a diameter between 0.5 and 5 µm) on top. Raman scattering from the thin Si layer exhibits enhancements (~20) due to the dielectric spheres, where the enhancement factors depend on the diameter of the spheres. The interaction between light and dielectric spheres has been simulated by finite difference time domain calculations (FDTD), wherein particularly the electric energy density (ED) distribution in the thin Si layer was of concern. For microspheres with a diameter less than ~3 µm, the transverse ED distribution (perpendicular to the incident light direction) within the Si layer is characterised by a single peak centered on the optical axis. For larger diameters, a multimodal transverse ED distribution develops where the maximum is not centered on the optical axis. Using an ad‐hoc approach for surface enhanced Raman scattering in combination with the FDTD calculations, the experimental Raman observations are well accounted for. Copyright © 2013 John Wiley & Sons, Ltd.     

Liquid-like Raman scattering by superionic materials

The Raman spectrum of a superionic conductor, α-AgI, is compared with the spectra of the melt of AgC$\text{l}$ and AgBr, in order to determine the responsible Raman processes. We conclude that because of the strong anharmonicity and high translational disorder in superionic conductors, spectra analyses based on the concept of harmonic lattice are unsuitable. A dynamical picture of ions similar to that of liquids appears to be more useful than the phonon concepts.     

Raman scattering by zigzag fluoropolymer molecules

The Raman spectra of ultrafine powders consisting of F(CF₂)_nF fluoropolymer zigzag molecules treated as a one-dimensional nanocrystal are investigated. These spectra are compared with the Raman spectra of C_nF_2n+1Br compounds (n=6–10 and 14) and fluoroplastics. It is found that the frequencies of optical vibrations of F(CF₂)_nF fluoropolymer molecules are shifted by more than 10 cm^?1 with respect to the relevant frequencies of C₆F₁₃Br molecules. The length of nanoparticles comprising an organofluoric ultrafine powder is estimated to be L=2–2.5 nm. This estimate is obtained from the measured frequency shifts in terms of the vibrational theory for a crystalline diatomic chain of finite length.     

The buildup of stimulated Raman scattering from spontaneous Raman scattering

We present a quantum electrodynamic theory which shows for the first time how stimulated Raman scattering builds up, both spatially and temporally, from spontaneous Raman scattering. We analytically solve operator Maxwell-Bloch equations to find the Stokes field operator, and thus the Stokes intensity, for both monochromatic and broad-band (phase diffusion) pump lasers.     

用染料激光增益降低二元混合物中少量化合物的受激拉曼散射可探测浓度

在二元混合物构成的圆形谐振腔中,用染料的激光增益增强了少量化合物(乙醇溶液中的甲醇、水溶液中的乙醇)的受激拉曼散射（SRS）光谱,将少量化合物在悬垂液滴中的瞬态SRS探测极限提高了近一个数量级. 用受激拉曼散射理论,解释了增强少量化合物SRS的机理. 关键词： 受激拉曼散射 染料激光增益 二元混合物 最小可探测浓度     

Enhancement of stimulated Raman scattering of acetone and the generation of three-color laser by using fluorescence dye RB

The enhancement of stimulated Raman scattering (SRS) of acetone (C3H6O) and the generation of threecolor lasers in lasing dye rhodamine B (RB) were reported. The first-order Stokes wave (629.9 nm) of SRS of C3H6O was amplified by 2.83 times than that of pure CsH6O. At the same time, a dye laser of RB at the wavelength from 575 to 598 nm can be generated in a suitable concentration of RB between 3×10-5and 2×10-4 mol/L. Thus the green pump laser, yellow dye laser, and red Stokes wave concurred.     

Raman scattering of light by 2LO-phonons

A theory of resonance Raman scattering of light by 2LO-phonons in semiconductor crystals is presented. Wannier excitons are considered as intermediate states. Analytic expressions are obtained that take into account contributions from different chains of intermediate states. The scattering cross section is shown to be weakly dependent on the wave vector imparted to the phonon system. The theoretical model permits the calculation of the scattering cross section for the energy of the exciting radiation photon below the level of exciton resonances.     

Enhanced Raman scattering provided by fullerene nanoclusters

Two new nonlinear optic effects are observed in crystalline solutions of fullerenes in toluene and carbon tetrachloride. Both are provided by a self-clustering of the solute molecules and are referred to fullerene-enhanced Raman scattering and solvent-enhanced luminescence. The effects are induced by the excitation of charge-transfer states of the fullerene nanoclusters, which makes the latter act as amplifiers of local electric fields. The text was submitted by the authors in English.     

Pulse-induced Raman scattering

The kinetic equations are used to show that induced Raman scattering can reduce the pulse height and length, and also can split a single pulse into several short pulses of decreasing energy. General formulas are derived for the pulse characteristics.     

Raman scattering by phonon polaritons in ZnS

The experimental difficulties in recording the phonon-polariton spectra of ZnS crystals are discussed. The measured polariton dispersion in cubic ZnS is presented and is found to be in good agreement with the calculated one.