Rayleigh Peak Research Articles

LIGHT SCATTERING FROM EXOPLANET OCEANS AND ATMOSPHERES

Orbital variation in reflected starlight from exoplanets could eventually be used to detect surface oceans. Exoplanets with rough surfaces, or dominated by atmospheric Rayleigh scattering, should reach peak brightness in full phase, orbital longitude = 180 deg, whereas ocean planets with transparent atmospheres should reach peak brightness in crescent phase near OL = 30 deg. Application of Fresnel theory to a planet with no atmosphere covered by a calm ocean predicts a peak polarization fraction of 1 at OL = 74 deg; however, our model shows that clouds, wind-driven waves, aerosols, absorption, and Rayleigh scattering in the atmosphere and within the water column, dilute the polarization fraction and shift the peak to other OLs. Observing at longer wavelengths reduces the obfuscation of the water polarization signature by Rayleigh scattering but does not mitigate the other effects. Planets with thick Rayleigh scattering atmospheres reach peak polarization near OL = 90 deg, but clouds and Lambertian surface scattering dilute and shift this peak to smaller OL. A shifted Rayleigh peak might be mistaken for a water signature unless data from multiple wavelength bands are available. Our calculations suggest that polarization alone may not positively identify the presence of an ocean under an Earth-like atmosphere; however polarization adds another dimension which can be used, in combination with unpolarized orbital light curves and contrast ratios, to detect extrasolar oceans, atmospheric water aerosols, and water clouds. Additionally, the presence and direction of the polarization vector could be used to determine planet association with the star, and constrain orbit inclination.

Rayleigh and Brillouin scattering in a lysozyme–water mixture: An unusual behavior around 343 K

This article describes Rayleigh and Brillouin light scattering studies on a lysozyme–water mixture from 293 K to 355 K. The scattering intensities from this system are compared with those from a sodium acetate buffer used to dissolve the lysozyme. It is found that in the vicinity of 343 K the lysozyme–water mixture becomes opalescent, and the intensity of the Brillouin peaks decreases and almost vanishes, to be restored at temperatures above 343 K. Around the same temperature the intensity of the central, unshifted Rayleigh peak, however, increases strongly. No such behavior was observed for the sodium acetate buffer. The analysis of the experimental data indicates an irreversible transition, near 343 K, from a metastable buffered system containing folded lysozyme molecules to a multimolecular gel of thermally unfolded lysozyme molecules.

Dynamic structure factor of the normal Fermi gas from the collisionless to the hydrodynamic regime

The dynamic structure factor of a normal Fermi gas is investigated by using the moment method for the Boltzmann equation. We determine the spectral function at finite temperatures over the full range of crossover from the collisionless regime to the hydrodynamic regime. We find that the Brillouin peak in the dynamic structure factor exhibits a smooth crossover from zero to first sound as functions of temperature and interaction strength. The dynamic structure factor obtained using the moment method also exhibits a definite Rayleigh peak ($\ensuremath{\omega}~0$), which is a characteristic of the hydrodynamic regime. We compare the dynamic structure factor obtained by the moment method with that obtained from the hydrodynamic equations.

Structural properties of warm dense matter

We investigate the structure in warm dense matter by ab initio simulations and classical fluid equations. This comparison yields valuable information on the system properties such as effective ion-ion interactions and charge states. Extensions to systems with multiple ion species are discussed and the limits of reduced descriptions are demonstrated. The structural information is then used to predict the signal strength in x-ray scattering experiments which, in turn, can be used as diagnostics for warm dense fluids. Here, we need to consider the inelastic feature due to the dynamic response of free electrons as well as the elastic (Rayleigh) peak related to the static ion structure. In a last example, we apply ab initio simulations to calculate the ionic structure in highly excited graphite close to melting.

Dynamic and structural scalings of the complexation between pDNA and bPEI in semidilute and low‐salt solutions

Using a combination of static and dynamic laser light scattering, we investigated the complexation of a supercoiled plasmid DNA (pDNA, 10(4) bp) and a branched polyethyleneimine (bPEI, M(w) = 25 kD) in semidilute and low-salt aqueous solutions. Our results unearth some scaling laws for dynamic and structural properties of the resultant complexes (polyplexes) with different bPEI:pDNA (N:P) molar ratios. Namely, the average scattering intensity (<I>) and the average linewidth of the Rayleigh peak (<Gamma>) are scaled to the scattering vector (q) as <I> proportional, variant q(alpha(s) ) or <Gamma> proportional, variant q(alpha(D) ), where alpha(S) and alpha(D) are two N:P dependent scaling exponents. The N:P ratio strongly affects the complexation. When N:P < 2.0, the motions of the negatively charged and extended pDNA chains and the polyplexes are highly correlated so that they behave like a transient network with a fractal dimension. As the N:P ratio increases, nearly all of pDNA chains condensed and the overall charge of the polyplexes reverses to slightly positive, resulting in a turbid dispersion of large loose aggregates made of smaller, but more compact, polyplexes. Further increase of N:P finally disrupts large loose aggregates, leading to a homogeneous transparent dispersion of the polyplexes.

10.1007/s11447-008-2012-1

The coefficient α(θ) of ultrasound transmission from liquid 4He to an aluminum single crystal in intermediate, superconducting, and normal states at a temperature T ≈ 0.1 K is measured as a function of the polar angle θ at the azimuthal angle φ = 0. The experimental technique is based on the measurement of the Kapitza temperature jump at the interface between two media. The dependences of the transmission coefficient for the Rayleigh modes on the sound frequency (in the range 13–194 MHz) and the magnetic field strength are determined. It is demonstrated that the integrated transmission coefficient of the aluminum single crystal in the intermediate state at an angle θR larger than the critical value increases with an increase in the magnetic field strength. The integrals of the transmission coefficient in magnetic fields close to the field H c are independent of the frequency. In the vicinity of H = 0, the transmission coefficient at ν > 39 MHz increases only slightly with increasing frequency. At the lowest frequencies, the transmission coefficient increases anomalously as the frequency decreases. The experimental data are compared with the results obtained in the framework of the Andreev theory. Numerical calculations are performed and the dependences α(θ, φ) for bulk modes in the range corresponding to angles smaller than the critical value are constructed for the three principal planes of the crystal, i.e., the (001), (011), and (111) planes. The dependence α(θ) is obtained for the azimuthal angle φ = 0. The width of the Rayleigh peak is estimated.

Raman satellites in optical scattering from a laser-ablated Mg plume

Raman satellites have been observed in the scattering of a Nd:YAG laser 532 nm from a laser-ablated Mg plasma plume. We identify them as originating from transitions between the fine-structure components of the metastable 3s3p P0,1,2 level of Mg. We have calculated the cross sections for Raman and Rayleigh scattering from the metastable state. Comparison of the expected ratio of the satellites to the Rayleigh peak indicates the changing population fraction of the metastable states in the plume.

Spectra of molecular gases trapped in deep optical lattices

We study the spectral profile of Rayleigh scattered light from molecular species trapped in optical lattices created by strong fields in the ${10}^{16}\text{ }\text{W}\text{ }{\text{m}}^{\ensuremath{-}2}$ range. We show that, for lattices with well depths on the order of 100 K, the motional sidebands imparted on spectra are shifted from the central Dicke-narrowed Rayleigh peak by hundreds of MHz. Our calculations for these short duration (30 ns) lattices show that these spectral features appear even in room temperature gases suggesting a new technique for measuring gas composition based on the frequency offset of the sidebands. Finally, we study the role of field-induced molecular alignment within the lattice and calculate its effect on the shape and position of the sidebands.

Coefficient of ultrasound transmission from liquid helium to aluminum in the intermediate state at T ≈ 0.1 K

The coefficient α(θ) of ultrasound transmission from liquid 4He to an aluminum single crystal in intermediate, superconducting, and normal states at a temperature T ≈ 0.1 K is measured as a function of the polar angle θ at the azimuthal angle φ = 0. The experimental technique is based on the measurement of the Kapitza temperature jump at the interface between two media. The dependences of the transmission coefficient for the Rayleigh modes on the sound frequency (in the range 13–194 MHz) and the magnetic field strength are determined. It is demonstrated that the integrated transmission coefficient of the aluminum single crystal in the intermediate state at an angle θR larger than the critical value increases with an increase in the magnetic field strength. The integrals of the transmission coefficient in magnetic fields close to the field Hc are independent of the frequency. In the vicinity of H = 0, the transmission coefficient at ν > 39 MHz increases only slightly with increasing frequency. At the lowest frequencies, the transmission coefficient increases anomalously as the frequency decreases. The experimental data are compared with the results obtained in the framework of the Andreev theory. Numerical calculations are performed and the dependences α(θ, φ) for bulk modes in the range corresponding to angles smaller than the critical value are constructed for the three principal planes of the crystal, i.e., the (001), (011), and (111) planes. The dependence α(θ) is obtained for the azimuthal angle φ = 0. The width of the Rayleigh peak is estimated.

Stimulated Rayleigh and Brillouin scattering in a supercritical fluid

We report stimulated Brillouin and Rayleigh scattering experiments in n-hexane for a wide range of subcritical and supercritical temperature and pressure conditions, including the near-critical region. The measurements were performed in a cell designed for operation at conditions near or above the critical point. An injection-seeded Nd:YAG laser was employed as the pump laser and an external cavity diode laser as the probe laser. The use of 1064-nm light enhances stimulated Rayleigh scattering through direct thermal absorption. Analysis of the recorded spectra yielded the widths, shifts, and heights of the electrostrictive Brillouin, thermal Brillouin, and thermal Rayleigh peaks. Comparison of these features with theory has showed consistency with the theoretical predictions of the relationships between the heights and widths of the thermal Brillouin and thermal Rayleigh peaks. Remarkable structure and sudden changes in the behavior of the Brillouin shifts, widths, and heights were observed in the vicinity of the critical region.

Detection of Residual Stress in Silicon Carbide MEMS by μ-Raman Spectroscopy

AbstractMicro-Raman (μ-Raman) spectroscopy is used to measure residual stress in single-crystal, 6H-silicon carbide (SiC) used in micro-electro-mechanical-systems (MEMS) devices. These structures are bulk micro-machined by back etching a 250-μm-thick, single-crystal 6HSiC wafer (p-type, 7 Ω-cm, 3.5° off-axis) to form a 50-μm thick diaphragm. A Wheatstone bridge, patterned of piezoresistive elements, is formed across the membrane from a 5-μm, 6HSiC (n-type, doped 3.8 × 1018 cm-3) epilayer; the output of the bridge is proportional to the flexure of the MEMS diaphragm. For these samples, the μ-Raman spectroscopy is performed using a Renishaw InVia Raman spectrometer with an argon-ion excitation source (λ = 514.5 nm, hν = 2.41 eV) with an approximate 1-μm2 spot size through the 50X objective. By employing an incorporated piezoelectric stage with submicron positioning capabilities along with the Raman spectral acquisition, spatial scans are performed to reveal areas in the MEMS structures that contain residual stress. Shifts in the transverse optical (TO) Stokes peaks of up to 2 cm-1 along the edge of the diaphragm and through the piezoresistors indicate significant material strain induced by the MEMS fabrication process.The phonon deformation potential is measured to quantify the material stress as a function of the shift in the Raman peak position. The line center of the TO Stokes peak is shifted by applying a uniform stress to the sample and monitoring the applied stress using a strain gauge, while the μ-Raman spectrum is being measured. A spectral analysis code tracks the shift of the Raman peak position with respect to the line center of the Rayleigh peak to account for any thermal drift of the spectrometer during the time of the area scan.

Dissolved organic fluorophores in southeastern US coastal waters: correction method for eliminating Rayleigh and Raman scattering peaks in excitation–emission matrices

Fluorescence-based observations provide useful, sensitive information concerning the nature and distribution of colored dissolved organic matter (CDOM) in coastal and freshwater environments. The excitation–emission matrix (EEM) technique has become widely used for evaluating sources and sinks of CDOM. Water scattering peaks, however, can create problems for quantitative analysis and display of the EEMs, especially for samples with low CDOM concentrations. Here we report a new method for eliminating Rayleigh and Raman scatter peaks from EEMs during post-processing of the data in MATLAB®. An algorithm was developed to excise scatter peaks (i.e. peak emission±10–15 nm at each excitation wavelength) from the scan data and replace the excised values using three-dimensional interpolation of the remaining data (Delaunay triangulation method). The interpolated surface was constrained to pass through the non-excised values so that only data in excised portions were replaced. Tests of the algorithm in non-scatter regions indicate expected deviations of 0–4% for interpolated regions of DOM fluorescence peaks (i.e. difference between measured and interpolated intensity after removal/interpolation), which is within machine error for the primary observations. This new scattering correction method is shown to provide much improved results in the quantitative analysis of EEMs compared to the conventional blank-subtraction procedure. The method is used to process EEMs and fluorescence quantum yields for water samples obtained along a salinity transect in a river located on the coast of the southeastern United States. Results of this analysis demonstrate observed shifts in EEM peak positions along most of the transect cannot be accounted for by a simple model that computes EEMs as a function of salinity assuming that the dominant driver of EEM spectral change is mixing between riverine and marine waters within the estuary. Other results show that fluorescence apparent quantum yields (AQYs) increased with increasing salinity and pH in the estuary and that the highest quantum yields are observed on excitation by 350–380-nm light. Modeling results and the observed EEM spectral changes indicate that photoreactions had an important effect on the fluorescent dissolved organic matter (FDOM) optical properties in the estuary. The increase in fluorescence quantum yields with increasing salinity and pH in the estuary likely were caused by reactions involving magnesium or hydroxide ions that reduced fluorescence quenching by chelated iron and possibly other paramagnetic ions. The results of the study indicate that EEM analysis with careful scatter correction can provide a powerful tool for evaluating pathways for carbon cycling in estuaries.

Assessing scattering effects in annular radioisotope excited XRF

AbstractRayleigh and Compton scattered radiation is used in various correction procedures for quantitative x‐ray fluorescence analysis. However, the information derived from the measured scatter peaks is altered by several phenomena in the case of annular radioisotope excitation, causing the calculated results to deviate, often significantly, from the expected values. In this work, we assessed the main sources of inaccuracy when using measured scatter intensities. Monte Carlo simulation was used to trace the radiation transport in the geometric arrangement source–sample–collimator–detector and to estimate the contribution of different effects to the measured Rayleigh and Compton scatter peaks. The information obtained in this way was used to extend the IAEA–QXAS standardless fundamental parameter approach to the case of annular radioisotope excitation and to formulate a method to correct for spurious fluorescent peaks appearing in blank measurements. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Very high energy gamma-rays from Centaurus X-3: Indications and implications

We present the results of a detailed timing analysis of observations of Cen X-3 taken by the University of Durham Mark 6 imaging atmospheric Cherenkov telescope in 1997{1999. The presence of a TeV -ray signal at the overall4:5 signicance level in the \fully image selected data, as reported earlier, is conrmed. A search for possible modulations of -rays with the pulsar spin period P0 4:8 s was performed by the step-by-step application of image parameter cuts of gradually increasing hardness. The data of each of 23 days of observations have not revealed any statistically signicant Rayleigh power peak, except for 1 day when a peak with a chance probability p =6 :8 10 7 was found in \soft-cut data sets. This modulation, if real, is blue shifted by 6.6 ms (>10 3 km s 1 ) from the nominal second harmonic of the X-ray pulsar. Taking the large number of frequency trials into account, the estimated nal probability of nding such a peak by chance still remains <10 2 . Bayesian statistical analysis also indicates the presence of such modulations. We show that the behaviour of the Rayleigh peak disappearing in the fully cut data set is actually quite consistent with the hypothesis of a -ray origin of that peak. No modulation of the VHE -ray signal with the pulsar orbital phase is found. In the second part of the paper we consider dierent theoretical models that could self-consistently explain the existing data from Cen X-3 in high-energy (HE, E 100 MeV) and very high energy (VHE, E 100 GeV) -rays. We propose on the basis of the energetics required that all reasonable options for the -ray production in Cen X-3 must be connected to jets emerging from the inner accretion disc around the neutron star. One of the principal options is a large-scale source, with Rs 10 13 10 14 cm; this assumes eective acceleration of electrons up to 10 TeV by shocks produced by interaction of these jets with the dense atmosphere of the binary. It is shown that such a quasi-stationary model could explain the bulk of the -radiation features observed except for the -ray modulations with the pulsar spin. These modulations, if genuine, would require an alternative source with Rs 10 11 cm. We consider two principal models, hadronic and leptonic, for the formation of such a compact source in the jet. Both models predict that the episodes of pulsed -ray emission may be rather rare, with a typical duration not exceeding a few hours, and that generally the frequency of pulsations should be signicantly shifted from the nominal frequency of the X-ray pulsar. The opportunities to distinguish between dierent models by means of future -ray observations of this X-ray binary are also discussed.

Critical Light Scattering in Pure Liquids

Light-seattering experiments near the eritical point (T c , ρ c ) in fluid systems and, in particular, the central Rayleigh peak in the frequency spectrum are reviewed. Within a nonasymptotic renormalization-group theory, the crossover function is calculated between several regions: (i) from the background to the asymptotic region, (ii) from the hydrodynamic region (wave length >> correlation length) to the critical region (wave length << correlation length), and (iii) from critical densities to noncritical densities. Contrary to the mode-coupling expression, the appropriate scaling function is well defined in all limits of its arguments. At T c the crossover in the wave-vector dependence of the linewidth is also considered. Theoretical results are compared with experiments for pure liquids. Nonuniversal parameters are chosen consistent with the transport coefficients (i.e., the shear viscosity) for the same substance which can be evaluated within the same formalism.

Critical light scattering in liquids

We compare theoretical results for the characteristic frequency of the Rayleigh peak calculated in one-loop order within the field theoretical method of the renormalization group theory with experiments and other theoretical results. Our expressions describe the nonasymptotic crossover in temperature, density, and wave vector. In addition we discuss the frequency dependent shear viscosity evaluated within the same model and compare our theoretical results with recent experiments in microgravity.

Discovery of chlorine in the Io torus

We report the discovery of singly ionized chlorine in the Io plasma torus through the detection of emission at 857.9 nm. The 40 Rayleigh peak intensity at 857.9 nm corresponds to a Cl+ abundance of 2±0.5% relative to all ions. Since Cl+ probably originates at Io, Io's atmosphere must have the highest proportion of chlorine of any solar system body. While Cl+ plays only a minor role in torus physics, the presence of chlorine in Io's atmosphere, surface, and interior has more profound implications. Salt as a solid or gas is probably an important source of both Na and Cl in Io's vicinity.

Quantitative energy-dispersive x-ray fluorescence analysis of liquids using partial least-squares regression

Energy-dispersive x-ray fluorescence in combination with partial least-squares regression (PLSR) was used to determine nickel, copper and arsenic in aqueous solutions. Different spectrum pre-processing methods (square root and logarithmic transformation and top hat filtering) were used prior to the PLSR calibration. An accuracy of better than 5% was obtained. The effect of the Rayleigh and Compton scatter peaks and the continuum on the performance of the PLSR method was investigated. The PLSR method was compared with the method of Lucas-Tooth and Price and showed similar results. Copyright © 1999 John Wiley & Sons, Ltd.

Molecular Dipole Chains: Excitations and Dissipation

As a model for orientational excitation of molecular arrays, we examine the excitation behavior and energy flow patterns in a model system. The model is simply a chain of classical point dipoles with fixed mass center, rotating in a plane containing the intermolecular axis, and interacting by the classical dipole potential. At low energies, the dispersion relation is quite different from that for a phonon system, showing a flat frequency maximum at k = 0. Correlation function analysis shows a significant transition from the low-energy regime in which the local dipole motion is predominantly oscillatory (with periodic correlation functions and Fourier components that maximize at a well-defined oscillation frequency), to a high-energy situation in which a Rayleigh peak occurs in the k = 0 Fourier component, and finite frequency response occurs only for higher wave vector. Physically, this transition occurs for thermal energy roughly equal to the typical magnitude of the local dipolar interaction. Thus for e...

Peculiarities of acoustic energy transmission from liquid helium to metals: A Review

Experimental and theoretical studies of the coefficient α of phonon energy transmission from liquid helium to cubic-symmetry metals (tungsten, copper, and aluminum single crystals and gold polycrystals) are reviewed briefly. It is shown that the transmission coefficients for single crystals with a perfect surface are correctly described by the theory of acoustic impedance mismatch model, taking into account absorption of phonons by conduction electrons. Andreev’s theory of electron resonant absorption of a Rayleigh wave by the surface of single crystal with α∼1 is confirmed. In a strongly anisotropic copper single crystal, a resonant pseudo-surface wave absorption peak is also observed. It is shown for aluminum that phonon dissipation decreases sharply upon a transition from the normal to superconducting state, and the height of the Rayleigh peak decreases accordingly. It is found that the main mechanism of phonon scattering in a polycrystal is the Rayleigh scattering at grain boundaries, which is proport...