共查询到20条相似文献,搜索用时 31 毫秒
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Using scattering theory we have derived an explicit expression for the time dependence of the resonant interaction of lorentzian photons with molecular systems. A discussion is presented on the dependence of molecular states on the nature of the exciting photon with an additional regard for the appropriate choice of basis sets. By examining the time dependence of the scattered photon a clear resonance Raman scattering resonance fluorecence limit emerges based on the temporal relationship of the scattered photon to that of the resonant state and incident photon. The influence on the resonant scattering of random fluctuation and relaxation processes that lead to dissipation is discussed with reference to scattering experiments performed in the gas and condensed phases. 相似文献
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ABSTRACTWe have carried out polarisation and angle-resolved measurements of the light scattered from photonic cholesteric liquid crystals. Both in samples doped with laser dyes and in inactive (non-doped) samples we have observed pronounced directional dependences of the scattered light, finding angular ranges where the scattering is greatly enhanced and regions where the effect is almost suppressed. Moreover, the total amount of scattered light has also been found to depend strongly on the polarisation and direction of the incident beam. All the results have been interpreted successfully in terms of a simple expression proposed for the scattering cross section, in which the density of states of the ingoing and outgoing beams plays a major role. The expression would be applicable not only to cholesteric liquid crystals but to any one-dimensional photonic material. 相似文献
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Aslan K Holley P Davies L Lakowicz JR Geddes CD 《Journal of the American Chemical Society》2005,127(34):12115-12121
We describe an exciting opportunity for affinity biosensing using a ratiometric approach to the angular-dependent light scattering from bioactivated and subsequently aggregated noble metal colloids. This new model sensing platform utilizes the changes in particle scattering from very small colloids, which scatter light according to traditional Rayleigh theory, as compared to the changes in scattering observed by much larger colloidal aggregates, formed due to a bioaffinity reaction. These larger aggregates no longer scatter incident light in a Cos(2) theta dependence, as is the case for Rayleigh scattering, but instead scatter light in an increased forward direction as compared to the incident geometry. By subsequently taking the ratio of the scattered intensity at two angles, namely 90 degrees and 140 degrees , relative to the incident light, we can follow the association of biotinylated bovine serum albumin-coated 20 nm gold colloids, cross-linked by additions of streptavidin. This new model system can be potentially applied to many other nanoparticle assays and has many advantages over traditional fluorescence sensing and indeed light-scattering approaches. For example, a single nanoparticle can have the equivalent scattered intensity as 10(5) fluorescing fluorescein molecules substantially increasing detection; the angular distribution of scattered light from noble metal colloids is substantially easier to predict as compared to fluorescence; the scattered light is not quenched by biospecies; the ratiometric measurements described here are not dependent on colloid concentration as are other scattering techniques; and finally, the noble metal colloids are not prone to photodestruction, as is the case with organic fluorophores. 相似文献
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The Compton scattering of 59.54 keV gamma rays by an Al scatterer has been used as a primer source at scattering angles from 48 to 118° by using a Si(Li) detector, and this primer gamma ray has been send to absorbers including Gd, Tb, Dy, Ho and Er. A new method has been developed to determine the K-shell absorption jump factor of elements and compounds. This method is based on simultaneous measurement of fluorescence radiation and scattered radiation, thus avoiding the problems with measuring the source strength and source-to-detector solid angle. In this method, the jump factor is effected from the scattering angle. Evident energies near to K-absorption edges of each lanthanide element have been determined for chosen angles, after the incident photon energy (59.5 keV) is exposed to Compton scattering from Al (secondary source). The experimental absorption jump factors are compared with the theoretical estimates and literature experimental values. 相似文献
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A. Kumar M. Balasubramaniam A. Chakraborty B. P. Crider S. F. Hicks C. Karthikraj L. J. Kersting C. J. Luke P. J. Mcdonough M. T. McEllistrem E. E. Peters F. M. Prados-Estévez A. J. Sigillito M. M. Upadhyay J. R. Vanhoy S. W. Yates 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(2):1043-1047
Elastic neutron scattering angular distributions from 23Na have been measured for incident neutron energies between 1.0 and 4.0 MeV at the University of Kentucky Accelerator Laboratory using neutron time-of-flight techniques for the scattered neutrons. This is an energy region in which existing data are very sparse. Measurements are compared with the predictions of the light particle-induced reaction code TALYS. The calculations reproduce forward angle scattering but have difficulty with relative minima in the differential cross section and large-angle scattering. 相似文献
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Corrections to dipole approximation results for angular distributions in photoionization of first-row hydrides have determined by using Dyson orbitals calculated with ab initio electron propagator theory and by considering the full multipole expansion for the incident photon representation. The relative importance of first-order corrections which consist of electric quadrupole and magnetic dipole terms and of higher-order terms has been estimated as a function of photon energy. Multipole corrections to the dipole approximation depend on photon energy and on the characteristics of the Dyson orbitals. 相似文献
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Feng DH Xu ZZ Feng XL Jia TQ Li XX Liu JS 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(4):575-578
Incoherent subharmonic light scattering in isotropic media is a new kind of nonlinear light scattering, which involves single input photon and multiple output photons of equal frequency. We investigate theoretically the dependence of the subharmonic scattering intensity on the hyperpolarizability of molecules and the incident intensity using nonlinear optics theory similar to that used for Hyper-Rayleigh scattering and degenerate optical parametric oscillators. It is derived that the subharmonic scattering intensities grow exponentially or superexponentially with the hyperpolarizability of molecules and the incident intensity. 相似文献
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Molecular motion in polymer networks and concentrated solutions from photon correlation spectroscopy
The dynamics of well-characterised polymer networks have been studied from Rayleigh light scattering linewidth measurements using photon correlation spectroscopy. The linewidth dependence on scattered wave-vector and on the degree of chemical cross-linking can be described by a model of whole molecule diffusion which is restricted by certain sites along it being cross-linked into the network. Linewidths of uncross-linked polymer solutions of similar concentrations have been found to be smaller by about a factor of two. 相似文献
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Glatzel P Bergmann U Gu W Wang H Stepanov S Mandimutsira BS Riordan CG Horwitz CP Collins T Cramer SP 《Journal of the American Chemical Society》2002,124(33):9668-9669
The potential of 1s2p resonant inelastic (Raman) X-ray scattering (RIXS) is demonstrated for a series of Ni coordination complexes. In this technique, incident and scattered photon energies lie in the hard X-ray range (>5 keV). The 1s2p RIXS contour plots provide information that is complementary to K-edge and L-edge spectroscopy. RIXS spectroscopy promises to be a valuable probe of electronic structure 相似文献
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Clark SC Walz JY Ducker WA 《Langmuir : the ACS journal of surfaces and colloids》2004,20(18):7616-7622
We describe the use of evanescent wave scattering to measure the separation between the surface of a solid and a particle that is attached to an atomic force microscope (AFM) cantilever. Termed evanescent wave atomic force microscopy, our approach involves measuring the intensity of the light scattered from an evanescent field formed by the total internal reflection of a laser beam at a solid/fluid interface. In a conventional AFM "colloid probe" measurement, this separation must be inferred from an examination of the surface forces. Direct measurement of this separation with an evanescent wave atomic force microscope (EW-AFM) removes some ambiguity in the surface force measurement and, in addition, allows new types of measurements. For example, the force can be monitored at a constant separation. Our evanescent scattering apparatus is essentially identical to that used in total internal reflection microscopy (TIRM), except that we collect the light that scatters back into the incident medium, because the AFM partly obscures the forward scattered light (i.e., light scattered into the transmitted region). Compared to a conventional TIRM measurement, where the particle moves freely, attaching the particle to the cantilever in an EW-AFM gives much greater control of the particle position. 相似文献
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《Radiation Physics and Chemistry》2006,75(10):1380-1396
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Abstract– We have observed transient changes in the curvature of purple membrane fragments upon photoexcitation as a function of the pH of the suspending medium. The room temperature suspensions have low ionic strengths, and the bending is observed by changes in the scattered light at 320 nm. The photoexcitation is from a 20 ns laser pulse at 532 nm. We use a simple first-order approximation to subtract any changes in the scattered light associated with transient absorption changes during the photocycle. The resultant scattering curves are then fitted to the sum of three fundamental bending processes. Each process has an exponential rise, an exponential decay and an amplitude. We model two of the processes as transient forces correlated with the charge motion during the photocycle. The third process is probably cuased by local changes in the pH as the protein pumps protons. However, this is not proved rigorously. Additional experiments are proposed. 相似文献
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《Radiation Physics and Chemistry》2008,77(9):991-995
The gamma photons continue to soften in energy as the number of scatterings increases in the target having finite dimensions both in depth and lateral dimensions. The number of multiply scattered photons increases with an increase in target thickness, and saturates at a particular value of the target thickness known as saturation thickness (depth). The present measurements are carried out to study the energy dependence of saturation thickness of multiply scattered gamma photons from targets of various thicknesses. The scattered photons are detected by a properly shielded NaI(Tl) gamma ray detector placed at 90° to the incident beam. We observe that the saturation thickness increases with increasing incident gamma photon energy. Monte Carlo calculations based upon the package developed by Bauer and Pattison [Compton scattering experiments at the HMI (1981), HMI-B 364, pp. 1–106] support the present experimental results. 相似文献
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Aurelia Cionga Viorica Florescu 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,2(1):49-59
We consider Rayleigh scattering from a hydrogenlike atom in an arbitrary excitedn=2 state, and we investigate theoretically the dependence of the scattered radiation intensity and Stokes parameters on the state multipoles for the case of unpolarized incident radiation. Because in then=2 case Rayleigh scattering can not be accompanied by the change of the electron angular momentum, only 10 out of the 16 state multipoles influence the scattered radiation attributes. Our study reveals the existence of a measurable quantity which is determined only by Rayleigh scattering from 2p states. For the particular case of excitation by electron impact, some quantitative predictions are made, at the photon scattering angle ?=π/2, based on values for the state multipoles extracted from the literature (Blum and Kleinpoppen, Band). The vicinity of Balmer α and Lyman α resonances are studied in detail. 相似文献
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The extension of the photon correlation spectroscopy (PCS) in multiple scattering regime, so-called diffusing wave spectroscopy (DWS) was employed to the study of blood samples. Multiple scattered light from a helium-neon (He-Ne) laser beam incident on the blood samples was detected by a photomultiplier, and both the temporal autocorrelation intensity functions g 2(tau) and power spectra S(omega) were measured by a spectrum analyzer. The potentials of using DWS for the qualitative and quantitative determination of the structural characteristics of the blood elements were studied experimentally. The experimental studies made, permits the use of DWS for blood cells monitoring in a multiple scattering regime. This paper describes our initial attempts at applying DWS to the study of the discrete blood samples of both healthy donors and patients with the cardiac ischemia. The subsequent experiments provide a verification of DWS of blood cells shape monitoring under multiple scattering. 相似文献