Showing papers on "Acoustic interferometer published in 1984"

Short wavelength ion waves upstream of the Earth's bow shock

Abstract: The identification and explanation of short wavelength antenna interference effects observed in spacecraft plasma wave data have provided an important new method of determining limits on the wavelength, direction of propagation, and Doppler shift of short wavelength electrostatic waves. Using the ISEE-1 wideband electric field data, antenna interference effects have been identified in the ion waves upstream of the earth's bow shock. This identification implies that wavelengths of the upstream ion waves are shorter than the antenna length. The interference effects also provide new measurements of the direction of propagation of the ion waves. The new measurements show that the wave vectors of the ion waves are not parallel to the interplanetary magnetic field (IMF) as previously reported. The direction of propagation does not appear to be controlled by the IMF. In addition, analysis of the Doppler shift of the short wavelength ion waves has provided a measurement of the dispersion relation. The upper limit of the rest frame frequency was found to be on the order of the ion plasma frequency. At this frequency, the wavelength is on the order of a few times the Debye length. The results of this study now provide strong evidence that the ion waves in the upstream region are Doppler-shifted ion acoustic waves. Previously announced in STAR as N83-36328

Analysis of thermal generation of Rayleigh waves

Abstract: We have developed an analysis for thermal generation of surface acoustic waves (Rayleigh waves) valid for anisotropic materials. The analysis, based on the complex reciprocity relation, provides expressions for the mechanical displacement, the electrical potential, and the acoustic power density of the Rayleigh waves launched by harmonic heating of zones on the surface. These quantities are evaluated for an isotropic substrate. They are compared with those obtained by R. M. White in his work on thermal generation of bulk waves. Our theoretical results are in good agreement with two previous experiments carried out with a piezoelectric crystal of lithium niobate.

Ultrasonic liquid interface detector

Abstract: A sensor for detecting an interface of a liquid in a container comprises a transmitter and a receiver of ultrasonic waves, each situated outside the container, and coupled to the wall of the container by a strip waveguide. The transmitter is arranged to cause surface acoustic waves to propagate through a portion of the wall, and the receiver is arranged to detect waves derived from the transmitter. When the liquid is adjacent to the portion of the wall, mode conversion of the surface acoustic waves in the wall of the vessel into compression waves in the liquid causes a change in the energy of waves reaching the receiver.

Curvature effects in interferometry

Abstract: The phase shift in interferometry due to the space-time curvature is computed in nonrelativistic and relativistic physics This treatment is applied to an interferometer analogous to the perfect crystal interferometer used in the Colella-Overhauser-Werner experiment with thermal neutrons, an interferometer consisting of only horizontal mirrors, suitable for ultracold neutrons, and optical interferometry Experiments are proposed to detect the effect of the tidal forces of the Earth, Moon, and the Sun, for the first time in interferometry The phase shift in neutron interferometry due to terrestrial objects is considered and an experiment is proposed with superfluid helium as the source of gravity This would provide, for the first time, direct evidence concerning the gravitational interaction between two quantum-mechanical states The possibility of detecting purely general-relativistic effects due to curvature, by means of neutron interferometry, is also explored

Acoustooptical Phenomena in Liquid Crystals

Abstract: The review considers various aspects of the influence of mechanical deformation on the macroscopic structure and optical properties of liquid crystals: type of deformation (compression shear): deformation amplitude; relation between the acoustic wavelength, viscous wavelength, and liquid crystal layer thickness; mutual orientation of the wave vector and director; boundary conditions in the liquid-crystal cell (acoustically soft or acoustically rigid boundary); relation between the linear dimensions of the liquid crystal layer and the acoustic beam; acoustic parameters of the substrates of a liquid-crystal cell (stiffness, charactcriatic impedance, linear dimensions of the substrates vs. the acoustic wavelength). The following physical phenomena responsible for the orientation effects are discussed: acoustic flows, oscillating hydrodynamic flows, sound absorption, interaction between director oscillations and the velocity field. Specific features of acoustooptical phenomena near phase transitions ...

Laser Generation of Annular Converging Surface Acoustic Waves

Abstract: Converging surface acoustic waves have been generated and detected using a noncontacting technique. A YAG laser together with an axicon lens produces a focussed optical ring which excites both converging and diverging SAW on the test sample. An optical interferometer is used to measure the vertical displacement of the SAW. Variations in the surface acoustic waveforms due to different optical power, beam width and shape, as well as the anisotropic and dispersive properties of the samples are analyzed. The focussing effect and the resolution of the converging surface waves are illustrated. Applications of this technique, using a full or partial optical e xcitation ring, for characterization as well as nondestructive testing of materials are discussed.

Excitation of Surface Acoustic Waves Using Electron Acoustic Microscope

Abstract: A focused, modulated electron beam can generate acoustic bulk waves and surface acoustic waves (SAW) at the surface of a front specimen. By conventional electron acoustic microscope the acoustic bulk waves are detected by a piezoelectric transducer at the rear surface. In this paper, acoustic surface waves which are effectively excited by electron beams are detected at the surface of the specimen. This technique gives better imaging than the bulk wave detection.

A Critical Analysis of the Thermoacoustic Microscope

Abstract: A one-dimensional analysis of the inechani sms by which acoustic waves are generated in the thermoacoustic microscope is presented. Thermal waves and acoustic waves are treated as eigen-modes of the system, so that there is no acoustic wave generated by thermal waves in the bulk. It is then shown that there a re four channels by which the incident energy can be converted into acoustic energy which can produce an image. One is purely acoustic, and the others all involve mode-conversion of thermal waves to acoustic waves. An important consequence is that thermoacoustic microscope images can reflect different combinations of physical parameters than do images made with microscopes based on pure thermal wave scattering. scattering mechanisms to exhibit resolution which is much better than either the thermal or acoustic wave length. We comment on the ability of

Instability of a nonlinear Fabry–Perot interferometer

Abstract: A theoretical analysis is made of the operation of a Fabry–Perot interferometer containing a nonlinear (cubic) medium An instability of the operation of this interferometer in the presence of perturbations traveling at an angle to exciting plane waves appears at lower amplitudes than those necessary for the appearance of a hysteresis

Effect of Photo-Carriers on Acoustic Wave Propagation for Measuring Excess Carrier Density and Lifetimes in Silicon

Abstract: A new technique is described to measure temporal periodic fluctuations in the free-carrier density of s ilicon. It is based on the electronic dependence of the elastic constants, and involves the measurement of the perturbation in phase of an acoustic wave propagating through a region of modulated carrier density. An experlment is described in which the bulk lifetime of photogenerated carriers is determined using this technique. A theory is developed to predict the acoustic phase perturbation, and is found to agree well with experiment.

Strain-optic effect of acoustic waves generated in the edge-region of 45∘z KDP cuts

Abstract: Pulse response of electrooptic modulators made of 45∘Z KDP and ADP samples is investigated to determine the sources of piezoelectrically induced acoustic waves