Thin-film transducers for the detection and imaging of Brillouin oscillations in transmission on cultured cells

Mechanical imaging and characterisation of biological cells has been a subject of interest for the last twenty years. Ultrasonic imaging based on the scanning acoustic microscope (SAM) and mechanical probing have been extensively reported. Large acoustic attenuation at high frequencies and the use of conventional piezo-electric transducers limit the operational frequency of a SAM. This limitation results in lower resolution compared to an optical microscope. Direct mechanical probing in the form of applied stress by contacting probes causes stress to cells and exhibits poor depth resolution. More recently, laser ultrasound has been reported to detect ultrasound in the GHz range via Brillouin oscillations on biological cells. This technique offers a promising new high resolution acoustic cell imaging technique. In this work, we propose, design and apply a thin-film based opto-acoustic transducer for the detection in transmission of Brillouin oscillations on cells. The transducer is used to generate acoustic waves, protect the cells from laser radiation and enhance signal-to-noise ratio (SNR). Experimental traces are presented in water films as well as images of the Brillouin frequency of phantom and fixed 3T3 fibroblast cells

Near field enhancements from angled surface defects : a comparison of scanning laser source and scanning laser detection techniques

Enhancement of the Rayleigh wave signal amplitude at a surface defect, due to interference of incident, reflected and mode converted waves, has been reported by several authors, and it has been suggested that this could be used as a fingerprint of the presence of such cracking. The scanning laser line source technique in particular, where signal amplitude is enhanced as the laser generating the Rayleigh waves is in the region of a surface defect, has been reported as a suitable detection tool. However, the previous work has looked primarily at defects propagating normal to the surface, which may not always be a suitable approximation, and the enhancement measured when a detection laser rather than a generation laser is near a crack may, in some cases, be more significant. This work explores near field effects for both laser generation and laser detection points near a defect, and compares the enhancements for defects which are angled relative to the surface. We use a combination of finite element method models and experimental results, and probe enhancements of both the amplitude and frequency signals, and show that scanning the detection point may be a better method for locating surface defects if they are inclined at an angle to the surface

CHARGE DENSITY WAVES IN THE LAYERED TRANSITION METAL DICHALCOGENIDES

Les dichalcogénides de métaux de transition de groupe Va présentent une surface de Fermi reliable aux instabilités structurales. Dans des corps tels que IT-TaS2, ces effets apparaissent clairement dans les propriétés électromagnétiques qui sont anormales. Le but de l'article est de présenter des preuves expérimentales, en particulier par la diffraction des électrons et les rayons X, pour l'adoption d'un état fondamental CDW couple a une distorsion périodique de réseau. Nous montrons comment cet état fondamental peut être perturbé en intercalant des métaux alcalins ou des terres rares.The metallic layered transition metal dichalcogenides of group Va exhibit Fermi surface linked structural instabilities. In materials such as IT-TaS2, these effects readily manifest themselves in the electromagnetic properties, hitherto regarded as anomalous. The primary aim of the present paper is to present the diffraction evidence from electron and X ray observations, for the adoption of a charge density wave ground state coupled to a periodic lattice distortion, and to show how this ground state may be perturbed by alkali metal and rare earth intercalation