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A photoacoustic, laser ultrasonics based approach in an Impulsive Stimulated Scattering (ISS) implementation was used to investigate the texture in polycrystalline metal plates. The angular dependence of the 'polycrystalline' surface acoustic wave (SAW) velocity measured along regions containing many grains was experimentally determined and compared with simulated results that were based on the angular dependence of the 'single grain' SAW velocity within single grains and the grain orientation distribution. The polycrystalline SAW velocities turn out to vary with texture. The SAW velocities and their angular variations for {110} texture were found to be larger than that the ones for {111} texture or the strong γ fiber texture. The SAW velocities for {001} texture were larger than for {111} texture, but with almost the same angular dependence. The results infer the feasibility to apply angular SAW angular dispersion measurements by laser ultrasonics for on-line texture monitoring.

Results are presented on the thermal and elastic properties of a thin, 1.5 μm, nanocrystalline diamond coating (NCD), deposited on a silicon substrate by microwave plasma enhanced chemical vapor deposition. A combination of two all-optical measurement techniques, impulsive stimulated thermal scattering and grating induced laser beam deflection, was employed to launch and detect surface acoustic waves (SAWs). The relation between the dispersive propagation velocity of SAWs to the coating-substrate geometry is exploited to determine the elastic properties of the NCD coating. The elastic properties are found to be consistent with literature values. The thermal properties of the coating were determined by monitoring the thermal diffusion induced washing away of the laser induced transient surface temperature grating. The transient thermal grating signals were fitted by the low-frequency limit of a thermoelastic model for a multilayer configuration. Similar to the dispersion of the surface acoustic wave velocity, the characteristic time of the thermal diffusion driven grating decay evolves from a coating-dominated value at short grating spacings towards a substrate-dominated value at grating spacings well exceeding the coating thickness. The grating spacing dependence of the corresponding effective thermal diffusivity was experimentally determined and fitted, leading to a value for the thermal diffusivity of the NCD coating αNCD = 8.4− 0.1+ 2.7 mm2·s− 1, which is an order of magnitude lower than that of the silicon substrate. The low value of the thermal diffusivity is interpreted with a simple touching model.

The underlying working principle of detecting impulsive stimulated scattering signals in a differential configuration of heterodyne diffraction detection is unraveled by involving optical scattering theory. The feasibility of the method for the thermoelastic characterization of coating-substrate systems is demonstrated on the basis of simulated data containing typical levels of noise. Besides the classical analysis of the photoacoustic part of the signals, which involves fitting surface acoustic wave dispersion curves, the photothermal part of the signals is analyzed by introducing thermal wave dispersion curves to represent and interpret their grating wavelength dependence. The intrinsic possibilities and limitations of both inverse problems are quantified by making use of least and most squares analysis. publisher: Elsevier articletitle: Determination of thermoelastic material properties by differential heterodyne detection of impulsive stimulated thermal scattering journaltitle: Photoacoustics articlelink: http://dx.doi.org/10.1016/j.pacs.2015.05.001 content_type: article copyright: Copyright © 2015 The Authors. Published by Elsevier GmbH ispartof: PHOTOACOUSTICS vol:3 issue:2 pages:64-77 ispartof: location:Germany status: published

MnO2 is a material of interest in the development of high energy-density batteries, specifically as a coating material for internal 3D structures, thus ensuring rapid energy deployment. Its electrochemical properties have been mapped extensively, but there are, to the best of the authors' knowledge, no records of the elastic properties of thin film MnO 2. Impulsive stimulated thermal scattering (ISTS), also known as the heterodyne diffraction or transient grating technique, was used to determine the Young's modulus (E) and porosity (ψ) of a 500nm thick MnO2 coating on a Si(001) substrate. ISTS is an all optical method that is able to excite and detect surface acoustic waves (SAWs) on opaque samples. From the measured SAW velocity dispersion, the Young's modulus and porosity were determined to be E=25±1GPa and ψ = 42 ± 1 %, respectively. These values were confirmed by independent techniques and determined by a most-squares analysis of the carefully fitted SAW velocity dispersion. This study demonstrates the ability of the presented technique to determine the elastic parameters of a thin, porous film on an anisotropic substrate. © 2014 AIP Publishing LLC. ispartof: Journal of Applied Physics vol:116 issue:2 status: published

This paper describes the application of Impulse Stimulated Thermal Scattering (ISTS) for measurement of surface acoustic wave (SAW) velocity and thermal diffusion along a free surface of a strongly anisotropic material. The motivation for this work stems from the study of thermoelastic properties of individual phases of ferroelastics; experimental results were obtained on a single crystal in the austenitic phase a Cu-Al-Ni alloy (bcc single crystal having elastic anisotropy factor of about 12). The measured SAW velocities in specific directions are in a good agreement with the values calculated for the elastic constants obtained by other ultrasonic methods. Similarly, the evaluated thermal diffusivity coefficient (22 ± 2).10−6 m2/s of the austenite is consistent with the data in the literature. The proposed approach has also a potential for characterization of thin films grown on anisotropic substrates.