Revealing sub-{\mu}m inhomogeneities and {\mu}m-scale texture in H2O ice at Megabar pressures via sound velocity measurements by time-domain Brillouin scattering

Time-domain Brillouin scattering technique, also known as picosecond ultrasonic interferometry, which provides opportunity to monitor propagation of nanometers to sub-micrometers length coherent acoustic pulses in the samples of sub-micrometers to tens of micrometers dimensions, was applied to depth-profiling of polycrystalline aggregate of ice compressed in a diamond anvil cell to Megabar pressures. The technique allowed examination of characteristic dimensions of elastic inhomogeneities and texturing of polycrystalline ice in the direction normal to the diamond anvil surfaces with sub-micrometer spatial resolution via time-resolved measurements of variations in the propagation velocity of the acoustic pulse traveling in the compressed sample. The achieved two-dimensional imaging of the polycrystalline ice aggregate in-depth and in one of the lateral directions indicates the feasibility of three-dimensional imaging and quantitative characterization of acoustical, optical and acousto-optical properties of transparent polycrystalline aggregates in diamond anvil cell with tens of nanometers in-depth resolution and lateral spatial resolution controlled by pump laser pulses focusing.Comment: 32 pages, 5 figure

All Optical Pump Probe Setup for Austenitic and Casted Steel Study

Polycrystalline materials are the most natural form of metals and are commonly used in industry. In particular, steels such as austenitic steels and casted steels are widely used for their specific properties in fatigue and resistance to heat in particular for application such as water pipes for cooling system in nuclear technologies. Usually studied by an effective approach, the characterization of the composing grains remains an essential aspect of their global physical behavior. A sub nanosecond pump probe laser setup is used to generate and detect acoustic waves in a sample in order to explicit the anisotropy and morphology by the study of variations of velocities of surfaces waves. A statistical approach of the variation of flight time due to the anisotropy is used to estimate the elastic constants of the composing grains of an austenitic steel sample thanks to an inversion procedure. The method considers a distribution as a unique signature of the sample and allow an evaluation of the three elastic constants with a good agreement with the literature. The all optical setup is also used to scan the surface of a piece of casted steel and automatically measure the local velocities of surface acoustic waves which opens the way to cartography in velocity of the sample surface structure. The local variations of velocities inside the macro-grains is shown to be the proof of the presence of sub-structures of recurrent orientation

Beam shaping to enhance zero group velocity Lamb mode generation in a composite plate and nondestructive testing application

International audienceZero group velocity (ZGV) Lamb modes have already shown their potential in nondestructive testing applications as they are sensitive to the sample structural characteristics. In this paper, we first consider an aluminum sample to validate a method based on the beam shaping of the generation laser. This method is proven to enhance ZGV Lamb modes in aluminum, and then advantageously applied to a composite material plate. Finally, based on the proposed method, scanning the sample over healthy and flawed zones demonstrates the ability to detect subsurface flaws

High-Frequency Elastic Coupling at the Interface of van der Waals Nanolayers Imaged by Picosecond Ultrasonics

Although the topography of van de Waals (vdW) layers and heterostructures can be imaged by scanning probe microscopy, high-frequency interface elastic properties are more difficult to assess. These can influence the stability, reliability and performance of electronic devices that require uniform layers and interfaces. Here, we use picosecond ultrasonics to image these properties in vdW layers and heterostructures based on well-known exfoliable materials, i.e. InSe, hBN and graphene. We reveal a strong, uniform elastic coupling between vdW layers over a wide range of frequencies of up to tens of gigahertz (GHz) and in-plane areas of 100 _m2. In contrast, the vdW layers can be weakly coupled to their supporting substrate, behaving effectively as free standing membranes. Our data and analysis demonstrate that picosecond ultrasonics offers opportunities can probe the high-frequency elastic coupling of vdW nanolayers and image both perfect and broken interfaces between different materials over a wide frequency range, as required for future scientific and technological developments

Three-dimensional elasto-optical interaction for reflectometric detection of diffracted acoustic fields in picosecond ultrasonics

The three-dimensional 3D photoelastic interaction involved in the detection mechanism of picosecond ultrasonics is investigated in micrometric metallic films. In pump-probe experiments, the laser source beam is focused to a spot size of less than 1 μm. A 3D diffracted acoustic field is generated at high frequencies of several tens of gigahertz, containing longitudinal and shear waves altogether. Their propagation changes the dielectric permittivity tensor and the material becomes optically heterogeneous. Consequently, the detection process is modeled through the propagation of the laser probe beam in a material with dielectric properties varying in all directions. Thus, the solution of Maxwell's equations leads to a differential system, the source term of which is proportional to the acoustic field itself. In the frame of small perturbation theory, the latter is decomposed into a continuous sum of monochromatic plane waves. The scattered electromagnetic field is described using the matricant, and the ensuing analytical solution then allows analyzing the 3D photoelastic interaction. The contribution of acoustic diffraction and shear wave detection to the reflectometric signal is put into relief. Good agreement with experiments performed in a 1 μm thick aluminum film is found

Méthode optoacoustique non linéaire pour la détection et la caractérisation de fissures

Ce travail concerne la détection de fissure par une méthode optoacoustique non linéaire. Les échantillons sont des plaques de verre contenant une fissure de longueur centimétrique et de largeur micrométrique. La méthode développée est basée sur l absorption de deux lasers, indépendamment modulés, et focalisés au même endroit de l échantillon. Ceci génère deux ondes par expansion thermique. La première est une onde thermoélastique à basse fréquence fL (~Hz), et la seconde une onde acoustique à haute fréquence fH (dizaines de kHz). Quand une fissure est présente dans la zone échauffée, l onde thermoélastique peut la faire respirer. La fissure va se fermer (s ouvrir) quand l intensité du laser modulé à fL est haute (basse). Cette respiration influence l onde acoustique à fH générée à proximité. Il résulte un mélange de fréquence nonlinéaire, provoquant la génération de nouvelles fréquences : fH+-n fL (n=1,2, ). La détection de ces fréquences mélangées indique la présence d une fissure.This thesis deals with crack detection by a nonlinear optoacoustic method. The samples are glass plates containing a centimeter length and micrometer thick crack. The developed method is based on the absorption of two light beams, independently modulated, and focused at the same location on the sample. This causes the generation of two waves, by thermal expansion. The first one is a thermoelastic wave at low frequency fL (~Hz), and the second is an acoustical one at high frequency fH (tens of kHz). When a crack is present in the heated zone, the thermoelastic wave can make it breathe. The crack is expected to close (open) when the intensity of the heating laser modulated at fL is high (low). This breathing influences the acoustic wave generated in the vicinity of the crack at fH. It results a nonlinear frequency-mixing process, leading to the generation of new frequencies: fH+-n fL (n=1,2, ). The detection of these mixed-frequencies indicates the presence of a crack.LE MANS-BU Sciences (721812109) / SudocSudocFranceF

Elastic moduli of η-Ta2N3, a tough self-healing material, via laser ultrasonics

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