Application of the acousto-optic effect to pressure measurements in ultrasound fields in water using a laser vibrometer

A non-intrusive measuring technique, applied to sensing and measuring acoustic waves at ultrasonic frequencies is considered. The method is optically based and so does not interfere with the ultrasound field. The measurement procedure relies on the acousto-optic effect, that is the change in refractive index which occurs with changing pressure in the ultrasound field. This change in refractive index is detected through the change in the path length of a laser beam propagating through the region of interest. Typically these changes are small corresponding to a physical change of the order of 10–⁶ m. Fourier analysis is used to separate the component of the signal corresponding to the pressure variation from background noise and vibrations which can be dominant. Application of the technique is illustrated for an underwater ultrasound transducer. Measurements are made using the optical technique and compared to measurements taken with a hydrophone. The effectiveness of the optical measuring technique is discussed. It is shown that the laser vibrometer produces a good estimation of the mean beam pressure provided an estimation of the beam width is available, a restriction which is often satisfied; and the acoustic field can be assumed to be approximately constant across the beam

(Pb,Sr)TiO3 Films on SrTiO3 (100) Substrates Grown by Liquid Phase Epitaxy

International audiencePbTiO3 is a ferroelectric perovskite with a tetragonal structure at room temperature. It is extensively studied with different substitutions to obtain different polar phases and tunable piezoelectric and ferroelectric properties. One strategy is substitution on the Pb-site with Sr, within the (Pb,Sr)TiO3 solid solution, leading to a reduction in unit cell tetragonality, reaching cubic structure at room temperature for x=0.5 [Xing2003]. Controlling the Sr-content and thereby the structure gives the possibility to tune the electrical properties including reducing the Curie temperature, but also to stabilize a-domains depicting interesting nanoscale switching phenomena when grown as thin films [Matzen2014]. Here, we focus on presenting our work on epitaxial (Pb,Sr)TiO3 films synthesized by liquid phase epitaxy. This technique is applied for growing complex oxides on single crystalline substrates using a supersaturated solution comprising the desired oxide components of the film and a fitting solvent. Since it is a near thermodynamic equilibrium technique and the growth temperature is considerably lower than for bulk crystal growth, the defect concentration is often very low. By applying liquid phase epitaxy we have successfully grown films of Pb1-xSrxTiO3, with nominal compositions of x=0, 0.33, 0.39, and 0.43, on (100) SrTiO3 substrates. Energy dispersive X-ray measurements performed on selected films reveal an increase in the Sr-content for each nominally increase of Sr in the growth solution. Structural and spectroscopic investigations from X-ray diffraction and Raman spectroscopy at room temperature reveal all the investigated films are free of detectable impurities and possess tetragonal structure, with stable domain microscale patterning. In addition, for films with increasing Sr-content, the tetragonality decreases accordingly. These results confirm that we are able to control the composition and structure of the films by adapting the nominal composition of our growth solution. We will present and discuss the synthesisparameters applied for growth of the (Pb,Sr)TiO3 films by liquid phase epitaxy and the challenges encountered in relation to the growth. Structural and phononic fingerprints and domain patterning from X-ray diffraction and Raman spectroscopy will be presented as well as high temperature dependent studies, where we investigate the phase transitions.Our work underlines the successful growth of high crystalline quality films from the (Pb,Sr)TiO3 family by liquid phase epitaxy. We therefore hope these encouraging results can inspire others toexplore this synthesis route for ferroelectric materials [Wollesen].[Xing2003] X. Xing et al., “Solid solution Pb1− xSrxTiO3 and its thermal expansion”, Journal of alloys and compounds, vol. 360, issues 1-2, pp. 286-289, 2003.[Matzen2014] S. Matzen, et al. "Super switching and control of in-plane ferroelectric nanodomains in strained thin films.", Nature communications, vol. 5, pp. 1-8, 2014.[Wollesen] L. Wollesen et al. in preparation “Growth of (Pb,Sr)TiO3 Films by Liquid Phase Epitaxy”

Characterisation of LSO:Tb scintillator films for high resolution X-ray imaging applications

Within the framework of an FP6 project (SCINTAX)1 we developed a new thin film single crystal scintillator for high resolution X-ray imaging based on a layer of modified LSO (Lu2SiO5) grown by liquid phase epitaxy (LPE) on a dedicated substrate. In this work we present the characterisation of the scintillating LSO films in terms of optical and scintillation properties as well as spatial resolution performances. The obtained results are discussed and compared with the performances of the thin scintillating films commonly used in synchrotron-based micro-imaging applications

Characterisation of LSO:Tb scintillator films for high resolution X-ray imaging applications

Abstract Within the framework of an FP6 projec

Luminescent properties and energy transfer processes in Ce–Tb doped single crystalline film screens of Lu-based silicate, perovskite and garnet compounds

The work is dedicated to the development of scintillating screens based on the single crystalline films (SCF) of Ce,Tb doped Lu-based silicates, perovskites and garnets grown by the liquid phase epitaxy method. We confirm in this work the presence of the Ce → Tb energy transfer in LSO and LuAP hosts. We also show that in Ce–Tb doped LuAG SCF, the effective Tb → Ce energy transfer is observed. This results in increasing the light yield of the luminescence of double doped LuAG:Ce,Tb SCF up to 25–30% with respect to single Ce doped (Y,Lu)AG SCF counterparts at optimal ratio of Ce/Tb ions

A versatile indirect detector design for hard X-ray microimaging

International audienc