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ABSTRACT: We report on a high resolution inelastic UV scattering table-top setup conceived for Brillouin measurements. The system is based on a tandem 1+1 pass scanning Fabry-Perot interferometer of Sandercock type. Special optics were used in order to adapt such an interferometric device, nowadays only used at visible or IR wavelength, to the UV range. The advantages with respect to other UV Brillouin scattering instruments are the larger resolving power and the improved contrast in the low frequency spectral region. To corroborate these features we provide a comparison between data obtained using the described system and those from existing UV Brillouin scattering instruments.
The Review of scientific instruments 10/2012; 83(10):103102. · 1.52 Impact Factor
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ABSTRACT: We present an effective approach to determine the amount of energy absorbed by solid samples exposed to ultrashort laser pulses, thus, retrieving the maximum temperature attained by the ion lattice in the picosecond time scale. The method is based on the pyrometric detection of a slow temperature fluctuation on the rear side of a sample slab associated with absorption of the laser pulse on the front side. This approach, successfully corroborated by theoretical calculations, can provide a robust and practical diagnostic tool for characterization of laser-generated warm dense matter.
Physical Review Letters 07/2012; 109(2):025005. · 7.37 Impact Factor
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ABSTRACT: Combined Brillouin spectra collected at visible, ultraviolet, and x-ray frequencies are used to reconstruct the imaginary part of the acoustic compliance J'' over a wide frequency range between 0.5 GHz and 5 THz. For liquid, supercooled, and glassy glycerol, J'' is found to be linearly dependent on the tagged-particle susceptibility measured by incoherent neutron scattering up to ≃1 THz, giving evidence of a clear relation between acoustic power dissipation and density of states. A simple but general formalism is presented to quantitatively explain this relation, thus clarifying the connection between the quasielastic component observed in neutron scattering experiments and the fast relaxation dynamics probed by Brillouin scattering.
Physical Review Letters 04/2011; 106(15):155701. · 7.37 Impact Factor
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6th International Discussion Meeting on Relaxations in Complex Systems, Rome; 01/2011
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ABSTRACT: We report high-resolution, high-statistics inelastic x-ray scattering measurements of the dynamic structure factor of water as a function of momentum and energy transfer in various thermodynamic conditions, including high-pressure liquid near the melting point, supercooled liquid and polycrystalline ice. For momentum transfer values below 8 nm−1, two collective excitations associated with longitudinal and transverse acoustic modes were observed. Above 8 nm−1, another excitation was detected in the liquid. Comparison with polycrystalline data and molecular dynamics simulations suggests that this mode is related to longitudinal–transverse mixing of mode symmetry.
New Journal of Physics 05/2010; 12(5):053008. · 4.18 Impact Factor
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ABSTRACT: We measured the dynamic structure factor of the liquid and glassy phases of the LiCl-6H(2)O solution by means of inelastic scattering of radiation in the visible, UV, and x-ray range, between 1 GHz and 10 THz, and by means of photon-correlation spectroscopy, between 0.01 Hz and 20 kHz. The measurements were performed in the temperature range between 353 and 80 K. Our data show that a single-relaxation process exists at high temperature, which has features similar to those of the single relaxation of pure water. Upon cooling the system below approximately 220 K, this single mode starts to differentiate two processes, a structural (alpha-) and a secondary (beta-) relaxation. As the temperature is decreased, the beta-relaxation is the vanishing continuation of the single, high-temperature process, while the onset of the alpha-relaxation occurs at the expense of the beta-process.
The Journal of chemical physics 10/2009; 131(15):154507. · 3.09 Impact Factor
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ABSTRACT: The density and temperature dependence of the structural relaxation time (tau) in water was determined by inelastic ultraviolet scattering spectroscopy in the thermodynamic range (P=1-4000 bars, T=253-323 K), where several water anomalies take place. We observed an activation (Arrhenius) temperature dependence of tau at constant density and a monotonic density decrease at constant temperature. The latter trend was accounted for by introducing a density-dependent activation entropy associated to water local structure. The combined temperature and density behavior of tau indicates that differently from previous results, in the probed thermodynamic range, the relaxation process is ruled by a density-dependent activation Helmholtz free energy rather than a simple activation energy. Finally, the extrapolation of the observed phenomenology at lower temperature suggests a substantial agreement with the liquid-liquid phase transition hypothesis.
The Journal of chemical physics 10/2009; 131(14):144502. · 3.09 Impact Factor
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M.E. Gallina,
L. Comez,
S. Perticaroli,
A. Morresi,
A. Cesàro,
O. De Giacomo,
S. Di Fonzo, A. Gessini,
C. Masciovecchio,
L. Palmieri,
M. Paolantoni,
P. Sassi,
F. Scarponi,
D. Fioretto
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ABSTRACT: The dynamics of density fluctuations of aqueous glucose solutions were studied in the water-rich region by means of Brillouin ultra-violet scattering. The temperature dependence of the position and line-width of inelastic peaks gives evidence of a strong relaxation process located in the picosecond timescale. In the approximation of a single exponential process, the relaxation time, τ, was obtained for different glucose concentrations; its temperature dependence is well described by an Arrhenius law characterized by an activation energy comparable to that of pure water. This result supports the hypothesis that the microscopic mechanism responsible for the main relaxation process in sugar–water solutions is the continuum rearrangement of the hydrogen-bond network. A comparison is also reported with previous results on aqueous trehalose solutions, showing the acoustic absorption scales with the number of glucoside units for both glucose and trehalose aqueous solutions.
Philosophical Magazine 11/2008; 88(Nos. 33-35):3991-3998. · 1.51 Impact Factor
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Condensed Matter Physics 01/2008; 11:47. · 0.81 Impact Factor
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XI International Workshop on Complex Systems; 01/2008
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5th International Workshop on Complex Systems, Sendai (Japan); 01/2008
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ABSTRACT: A Brillouin scattering investigation has been carried out on trehalose-water solutions in a wide range of concentrations (0<phi<0.74) in the ultraviolet regime. A complete set of data as a function of temperature (-10 degrees C<or=T<or=100 degrees C) has been obtained for each concentration. The T-phi evolution of the system has been analyzed in terms of energy position and line width of inelastic peaks. These results have been used to derive the structural relaxation time, tau, of the system. This was found to be in the tens of picoseconds time scale, and its T dependence can be described with an activation (Arrhenius) law. Most importantly, a significant slowing down of the relaxation dynamics has been observed as trehalose concentration was increased. At low phi, the activation energy of the relaxation has been found to be consistent with literature data for pure water and comparable with intermolecular hydrogen bond (HB) energy. This evidence strongly supports the hypothesis that the main microscopic mechanism responsible for the relaxation process in trehalose solutions lies in the continuous rearrangement of the HB network. Finally, the results are discussed in terms of the evolution of the system upon increasing trehalose concentration, in order to provide a complete description of the viscoelastic stiffening in real biological conditions.
The Journal of Physical Chemistry A 12/2007; 111(49):12577-83. · 2.95 Impact Factor
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ABSTRACT: We measured the dynamic structure factor S(Q,omega) of liquid and undercooled water down to 253 K in the Q approximately 0.02-0.1 nm;{-1} momentum transfer region. We observe the neat departure of the apparent speed of sound from the adiabatic regime as a function of decreasing temperature. Our evaluation of the infinite-frequency limit of sound velocity, c_{infinity}, matches with the results obtained in the high momentum transfer limit by inelastic neutron and x-ray scattering. These results strongly support the viscoelastic interpretation of the dynamics of water. Hence, we propose to call c_{infinity} the high-frequency speed of sound and to abandon the term fast sound, which recalls a propagation mechanism through lighter atoms, like in gas mixtures.
Physical Review Letters 01/2007; 97(22):225701. · 7.37 Impact Factor
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ABSTRACT: Among disaccharides, trehalose is demonstrated to be the most efficient bioprotecting agent against dehydration and freezing and it has been identified, at high concentration, in several natural organisms with important applications in the preservation of mammalian cells. However, despite its relevance in biopreservation, the physical mechanism underlying the effectiveness of trehalose has not yet been definitely clarified. One reason could rely on the experimental difficulty in measuring the dynamics of the trehalose–water system at high concentration, as its behaviour is often derived as an extrapolation from low-concentration data. In this report we present the results of a feasibility experiment in which the dynamic structure factor S(Q, ω) of a trehalose–water solution at high trehalose concentration (79% w) has been measured for the first time over a rather large temperature range (235 K < T < 343 K) by means of inelastic ultraviolet scattering at a momentum transfer of Q ≈ 0.1 nm−1. We observe a pronounced increase in the mode frequency upon cooling and a non-monotonic variation of the mode frequency width with a maximum at T ≈ 330 K, typical features of the structural relaxation of liquids approaching a glass transition.
Philosophical Magazine. 01/2007; 87(Nos. 3–5):623-630.
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C Masciovecchio,
G Baldi,
S Caponi,
L Comez,
S Di Fonzo,
D Fioretto,
A Fontana, A Gessini,
S C Santucci,
F Sette,
G Viliani,
P Vilmercati,
G Ruocco
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ABSTRACT: We report measurements of the sound attenuation coefficient in vitreous silica, for sound waves of wavelength between 50 and 80 nm, performed with the new inelastic UV light scattering technique. These data indicate that in silica glass a crossover between a temperature-dependent (at low frequency) and a temperature-independent (at high frequency) acoustic attenuation mechanism occurs at Q approximately equal to 0.15 nm(-1). The absence of any signature in the static structure factor at this Q value suggests that the observed crossover should be associated with local elastic constant fluctuations.
Physical Review Letters 08/2006; 97(3):035501. · 7.37 Impact Factor
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ABSTRACT: The dynamic structure factor of vitreous silica and glycerol has been measured as a function of temperature and of the momentum transfer up to Q=0.105 nm(-1) using a novel experimental technique, the inelastic ultraviolet scattering. As in the case of Brillouin light scattering and ultrasonic measurements, the temperature dependence of the acoustic attenuation shows a plateau below the glass transition whose amplitude scales as Q2. Moreover, a slight temperature dependence of attenuation has been found in vitreous silica at about 130 K, which seems to be reminiscent of the peak measured at lower Qs. These two findings strongly support the idea that anharmonicity is responsible for sound attenuation at ultrasonic and hypersonic frequencies. Finally, we demonstrate that the attenuation mechanism should show a change of regime between 0.105 and 1 nm(-1).
Physical Review Letters 07/2004; 92(24):247401. · 7.37 Impact Factor
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ABSTRACT: Using the novel synchrotron radiation based inelastic ultraviolet scattering technique, the dynamic structure factor of normal and supercooled liquid water has been measured at a momentum transfer Q approximately equal to 0.1 nm(-1), in the temperature range 260-340 K. The structural (alpha) relaxation has been observed in the supercooled temperature region (T< or =273 K), where the inverse relaxation time matches the frequency of the probed sound modes. The T dependence of the relaxation time shows a diverging behavior with a critical temperature T approximately equal to 220 K. These results provide a unique experimental opportunity to frame the dynamics of water in the mode-coupling theory.
Physical Review Letters 07/2004; 92(25 Pt 1):255507. · 7.37 Impact Factor
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ABSTRACT: One of the most important goals of condensed matter physics today is the experimental determination of the collective dynamical properties due to atomic, electronic and magnetic density fluctuations. These are responsible for specific vibrational, electronic and magnetic elementary excitations, which are often related to many macroscopic properties characteristic of the considered system. Our experimental challenge is the determination of the dynamic structure factor S(Q,E) related to collective density fluctuations, in the largest possible energy (E) and momentum transfer (Q) spaces. The recent construction of an Inelastic UltraViolet Scattering (IUVS) beamline at the ELETTRA Synchrotron Light Laboratory will allow studying collective dynamics in the unexplored mesoscopic momentum transfer region (0.05 to 0.25 nm-1 ). This region is of great interest for the study of the properties of collective excitations in many research fields at the frontier of condensed matter physics and chemistry (1). The IUVS spectrometer utilises an undulator source (namely a Figure-8 undulator), and is conceptually composed of three stages: the monochromator, the scattering sample and the analyser. The incident photon energy can be tuned in the 5-11 eV range by the monochromator, with an energy resolution in the 10-5 to 10-6 range. The analyser allows one to energy analyse photons scattered by the sample at a certain scattering angle, with an energy loss or an energy gain in the energy region typical of phonon like excitations in the considered momentum region. The energy resolution and tunability of the analyser is comparable to that of the monochromator. The momentum transfer, Q, is in the 0.02 to 0.25 nm-1 range, as allowed by the incident photon energy, by the choice of the scattering angle, and by the refractive index of the sample. The typical momentum resolution will be ∆Q/Q = 0.05. The spectrometer has allowed us to carry out test experiments on prototype samples such as liquid water and vitreous silica. In Fig. 1 the measured S(Q,E) of water at 40oC is shown in order to illustrate the possibilities offered by IUVS beamline. The instrument overall resolving power was set to 500000 at the incident photon energy of 6.7 eV. As the scattering angle is 176o, the resulting momentum transfer was 0.09 nm-1. One immediately observes the presence of well- defined phonon-like excitations peaks (Stokes and AntiStokes) on the sides of the elastic line in the
