A thorough experimental assessment of THz-TDS plasma diagnostic techniques for nuclear fusion applications.

In this paper, the study of a plasma diagnostic system based on the THz time domain spectroscopy technique is presented. Such a system could potentially probe a large part of the electromagnetic spectrum currently covered by several other diagnostics in a single measurement. This feature, keeping in mind the basic requirements for plasma diagnostics in nuclear fusion experiments, such as robustness and hard environment applicability, as well as durability and low maintenance, makes the diagnostic of great interest.

Gamma Irradiation Effect on Polymeric Chains of Epoxy Adhesive.

The study of materials for space exploration is one of the most interesting targets of international space agencies. An essential tool for realizing light junctions is epoxy adhesive (EA), which provides an elastic and robust material with a complex mesh of polymeric chains and crosslinks. In this work, a study of the structural and chemical modification of a commercial two-part flexible EA (3M™ Scotch-Weld™ EC-2216 B/A Gray), induced by Co gamma radiation, is presented.

Multi-length scale structural investigation of lysozyme self-assembly.

Reactive amyloid oligomers are responsible for cytotoxicity in amyloid pathologies and because of their unstable nature characterizing their behavior is a challenge. The physics governing the self-assembly of proteins in crowded conditions is extremely complex and its comprehension, despite its paramount relevance to understanding molecular mechanisms inside cells and optimizing pharmaceutical processes, remains inconclusive. Here, we focus on the amyloid oligomerization process in self-crowded lysozyme aqueous solutions in acidic conditions.

Temperature Dependence of Spin-Phonon Coupling in [VO(acac)]: A Computational and Spectroscopic Study.

Molecular electronic spins are good candidates as qubits since they are characterized by a large tunability of their electronic and magnetic properties through a rational chemical design. Coordination compounds of light transition metals are promising systems for spin-based quantum information technologies, thanks to their long spin coherence times up to room temperature. Our work aims at presenting an in-depth study on how the spin-phonon coupling in vanadyl-acetylacetonate, [VO(acac)], can change as a function of temperature using terahertz time-domain spectroscopy and density functional theory (DFT) calculations.

Pressure Effects on Water Dynamics by Time-Resolved Optical Kerr Effect.

Despite water being the most common and most widely studied substance in the world, it still presents unknown aspects. In particular, water shows several thermodynamic and dynamical anomalies in the liquid and supercooled metastable phases, and the natures of these phases are still hotly debated. Here, we report measurements of water using the optical Kerr effect as a function of pressure along two isotherms, at 273 K from 0.

Superheating and Homogeneous Melting Dynamics of Bulk Ice.

Homogeneous melting of crystals is a complex multistep process involving the formation of transient states at temperatures considerably higher than the melting point. The nature and persistence of these metastable structures are intimately connected to the melting process, and a precise definition of the temporal boundaries of these phenomena is not yet available. We set up a specifically designed experiment to probe by transient infrared absorption spectroscopy the entire dynamics, ranging from tens of picoseconds to microseconds, of superheating and melting of an ice crystal.

Time-domain THz spectroscopy of the characteristics of hydroxyapatite provides a signature of heating in bone tissue.

Because of the importance of bone in the biomedical, forensic and archaeological contexts, new investigation techniques are constantly required to better characterize bone ultrastructure. In the present paper, we provide an extended investigation of the vibrational features of bone tissue in the 0.1-3 THz frequency range by time-domain THz spectroscopy.

Spin Dynamics and Low Energy Vibrations: Insights from Vanadyl-Based Potential Molecular Qubits.

Here we report the investigation of the magnetization dynamics of a vanadyl complex with diethyldithiocarbamate (Etdtc) ligands, namely [VO(Etdtc)] (1), in both solid-state and frozen solution. This showed an anomalous and unprecedentedly observed field dependence of the relaxation time, which was modeled with three contributions to the relaxation mechanism. The temperature dependence of the weight of the two processes dominating at low fields was found to well correlate with the low energy vibrations as determined by THz spectroscopy.

Thin layered drawing media probed by THz time-domain spectroscopy.

Dry and wet drawing materials were investigated by THz time-domain spectroscopy in transmission mode. Carbon-based and iron-gall inks have been studied, some prepared following ancient recipes and others using current synthetic materials; a commercial ink was studied as well. We measured the THz signals on the thin films of liquid inks deposited on polyethylene pellicles, comparing the results with the thick pellets of dried inks blended with polyethylene powder.

Supercooling and freezing processes in nanoconfined water by time-resolved optical Kerr effect spectroscopy.

Using heterodyne-detected optical Kerr effect (HD-OKE) measurements, we investigate the vibrational dynamics and the structural relaxation of water nanoconfined in Vycor porous silica samples (pore size ≃ 4 nm) at different levels of hydration and temperatures. At low levels of hydration corresponding to two complete superficial water layers, no freezing occurs and the water remains mobile at all the investigated temperatures with dynamic features similar, but not equal to, the bulk water. The fully hydrated sample shows the formation of ice at about 248 K.

Picosecond optical parametric generator and amplifier for large temperature-jump.

An optical parametric generator and amplifier producing 15 ps pulses at wavelengths tunable around 2 μm, with energies up to 15 mJ/pulse, has been realized and characterized. The output wavelength is chosen to match a vibrational combination band of water. By measuring the induced birefringence changes we prove that a single pulse is able to completely melt samples of ice in the 10⁻⁶ cm³ volume range, both at room pressure (263 K) and at high pressure (298 K, 1 GPa) in a sapphire anvil cell.

Optical Kerr effect of liquid and supercooled water: the experimental and data analysis perspective.

The time-resolved optical Kerr effect spectroscopy (OKE) is a powerful experimental tool enabling accurate investigations of the dynamic phenomena in molecular liquids. We introduced innovative experimental and fitting procedures, that enable a safe deconvolution of sample response function from the instrumental function. This is a critical issue in order to measure the dynamics of liquid water.

Evidence of two distinct local structures of water from ambient to supercooled conditions.

The liquid and supercooled states of water show a series of anomalies whose nature is debated. A key role is attributed to the formation of structural aggregates induced by critical phenomena occurring deep in the supercooled region; the nature of the water anomalies and of the hidden critical processes remains elusive. Here we report a time-resolved optical Kerr effect investigation of the vibrational dynamics and relaxation processes in supercooled bulk water.

A comparative study on bulk and nanoconfined water by time-resolved optical Kerr effect spectroscopy.

The low frequency (nu < 500 cm(-1)) vibrational spectra of hydrated porous silica are specifically sensitive to the hydrogen bond interactions and provide a wealth of information on the structural and dynamical properties of the water contained in the pores of the matrix. We investigate systematically this spectral region for a series of Vycor porous silica samples (pore size approximately equal 4 nm) at different levels of hydration, from the dry matrix to completely filled pores. The spectra are obtained as the Fourier transforms of time-resolved heterodyne detected optical Kerr effect (HD-OKE) measurements.

Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers.

Optical frequency comb synthesizers have represented a revolutionary approach to frequency metrology, providing a grid of frequency references for any laser emitting within their spectral coverage. Extending the metrological features of optical frequency comb synthesizers to the terahertz domain would be a major breakthrough, due to the widespread range of accessible strategic applications and the availability of stable, high-power and widely tunable sources such as quantum cascade lasers. Here we demonstrate phase-locking of a 2.

The low frequency dynamics of supercooled LiBr, 6H2O.

We present results of a series of experiments performed on LiBr, 6H(2)0 from room temperature down to 172 K ≈ 1.2T(g). These ultrasound, Brillouin and depolarized light scattering, and transient grating experiments show that, above 215 K, this solution behaves like supercooled water: its zero frequency sound velocity C(0) continuously decreases with decreasing temperature, and the reorientational dynamics of the water molecules can be directly detected at some temperatures of this domain.

Inverse freezing in molecular binary mixtures of alpha-cyclodextrin and 4-methylpyridine.

Ternary solutions of alpha-cyclodextrin (alphaCD) in 4-methylpyridine (4MP)/water mixtures solidify when heated and melt when cooled, and the crystalline solid phase exhibits a rich phase behavior as a function of temperature. In this work, we extend these earlier investigations to pure binary mixtures of alphaCD in water free 4MP, characterized via temperature and time dependent measurements of viscosity, X-ray diffraction, and infrared spectroscopy, complemented by observations of acoustic properties and small angle neutron diffraction. At high concentrations (>500 g l(-1)), these solutions enter an amorphous solid phase not only with decreasing but also with increasing temperature, before crystallizing at higher temperatures.

The low frequency phonons dynamics in supercooled LiCl, 6 H2O.

We report the results of a series of ultrasound, Brillouin scattering, and optical heterodyne detected transient grating experiments performed on a LiCl, 6H(2)O solution from room temperature down to the vicinity of its liquid-glass transition, T(g) approximately 138 K. Down to T approximately 215 K, the supercooled liquid has a behavior similar to what is expected for supercooled water: its zero frequency sound velocity, C(0), continuously decreases while the corresponding infinite frequency velocity, C(infinity), sharply increases, reflecting the increasing importance of H bonding when temperature is lowered. Below 215 K, specific aspects of the solution, presumably related to the role of the Li(+) and Cl(-) ions, modify the thermal behavior of C(0), while a beta relaxation process also appears and couples to the sound propagation.

Analysis of a heterodyne-detected transient-grating experiment on a molecular supercooled liquid. II. Application to m-toluidine.

This paper reports the first detailed analysis of a transient grating (TG) experiment on a supercooled molecular liquid, m-toluidine, from 330K (1.75Tg) to 190K (1.01Tg) based on the theoretical model presented in Paper I of this series.

Analysis of a heterodyne-detected transient-grating experiment on a molecular supercooled liquid. I. Basic formulation of the problem.

We present the basic equations necessary to interpret heterodyne-detected transient-grating experiments performed on a supercooled liquid composed of anisotropic molecules. The final expressions are given under a form suitable for their direct application to a test case.

Supercooled water relaxation dynamics probed with heterodyne transient grating experiments.

We report results from a heterodyne-detected transient grating experiment on liquid and supercooled water in a wide temperature range, from -17.5 to 90 degrees C. The measured signal covers an extremely large time window with an excellent signal-to-noise ratio that enables the investigation in a single experiment of the sound speed and attenuation, thermal diffusivity, and temperature dependence of the dielectric constant.

Nonequilibrium thermodynamic description of the coupling between structural and entropic modes in supercooled liquids.

The density response of supercooled glycerol to an impulsive stimulated thermal grating (q=0.63 microm(-1)) has been studied in the temperature range (T=200-340 K) where the structure rearrangement (alpha relaxation) and the thermal diffusion occur on the same time scale. A strong interaction between the two modes occurs giving rise to a dip in the T dependence of the apparent thermal conductivity and a flattening of the apparent alpha-relaxation time upon cooling.

Relaxation processes in an epoxy resin studied by time-resolved optical Kerr effect.

The dynamics of the epoxy resin phenyl glycidyl ether, a fragile glass-forming liquid, is investigated in the liquid and supercooled phases by time-resolved optical Kerr effect experiment with an heterodyne detection technique. We tested the mode-coupling theory and found that the predicted dynamic scenario allows to reproduce properly the measured signal, for t>1 ps, in the whole temperature interval investigated. Furthermore, the values of T(c) and lambda, obtained from the analysis of three different and independent dynamic regimes (alpha regime, von Schweidler, beta regime), are in remarkable agreement.

Acoustic and relaxation processes in supercooled orthoterphenyl by optical-heterodyne transient grating experiment.

The dynamics of the fragile glass-forming orthoterphenyl have been investigated by transient grating experiments with an heterodyne detection technique. We measured the relaxation processes of this glass former over more than six decades in time with an excellent signal-to-noise ratio. Acoustic, structural, and thermal relaxations have been clearly identified in a time-frequency window not covered by previous spectroscopic studies and their characteristic dynamic parameters have been measured as a function of temperature and wave vector.