635 research outputs found
Imaging velocities of a vibrating object by stroboscopic sideband holography
We propose here to combine sideband holography with stroboscopic illumination
synchronized with the vibration of an object. By sweeping the optical frequency
of the reference beam such a way the holographic detection is tuned on the
successive sideband harmonic ranks, we are able to image the instantaneous
velocities of the object. Since the stroboscopic illumination is made with an
electronic device, the method is compatible with fast (up to several MHz)
vibration motions. The method is demonstrated with a vibrating clarinet reed
excited sinusoidally at 2 kHz, and a stroboscopic illumination with cyclic
ratio 0.15. Harmonic rank up to n = 100 are detected, and a movie of the
instantaneous velocities is reported
Development of Sound Presentation System (SPS) for Characterization of Sound Induced Displacements in Tympanic Membranes
The conventional methods for diagnosing pathological conditions of the tympanic membrane (TM) and other abnormalities require measuring its motion to an acoustic excitation for its use in a clinical environment. To obtain comprehensive quantitative diagnostic information from the motion of the entire surface of the TM, it is necessary to devise an integrated system capable of accurately recording the motion and induce an acoustic stimulus. To accomplish this goal, a sound presentation system (SPS) capable of impinging acoustic stimulus in the frequency range of 20Hz to 8 kHz at known amplitudes is synthesized in this thesis. This system is then integrated with optoelectronic digital holographic system (OEDHO) which utilizes laser interferometry to record and reconstruct phase shifted images with the help of a digital camera. The OEDHO is capable of accurately recording nanometer scale motion of the TM. The preliminary design of the SPS depends on the physical dimensions of the human ear, such as the diameter of the TM (6-9mm), depth of the ear canal (about 30mm), and also dimensions of the OEDHO system such as: diameter of tip of the otoscope head for optical access (8mm), and possible locations for integration with the OEDHO. The characteristics of the system are based on the intensity of the acoustic stimulus necessary to vibrate the TM (90-110dB SPL), and method of impinging the stimulus. To accomplish this goal, the nature of sound wave propagation through a circular pipe with known dimensions is analyzed analytically, experimentally, and by using finite element analysis (FEA). The pipe is further investigated for optimum parameters using FEA by introducing changes in the diameter (3.8mm, 6mm, 10mm), length of the pipe (30mm, 60mm, 90mm), radius of the curvature (50mm, 75mm, 100mm), and strength of the sound power source (0.2W, 0.4W, 0.6W). The comparative results provide guidelines for the design of the first version of the SPS (SPS_V1). The SPS_V1 consists of a symmetric design to impinge the acoustic stimulus towards the TM and a microphone to measure the sound pressure at the TM. The system is capable of housing a range of speakers from 2mm to 15mm in diameter. The SPS_V1 can directly interface with the standard medical speculums used for human ear testing. Also, the system is capable of interfacing with all available versions of the OEDHO. The SPS_V1 is currently being evaluated in a medical-research environment to address basic otological questions regarding TM function. The performance characterization of the system inside an artificial ear canal with two different speaker configurations is herein shown, and the potential improvements and utilization are discusse
Laser Doppler imaging of microflow
We report results obtained with a wide-field laser Doppler detection
scheme used to perform laser Doppler anemometry and imaging of
particle-seeded microflow. The optical field carrying the local
scatterers (particles) dynamic state, as a consequence of momentum transfer at each scattering event, is analyzed in the temporal frequencies domain. The setup is based on heterodyne digital holography, which is used to map the scattered field in the object plane at a tunable frequency with a multipixel detector. We show that wide-field heterodyne laser Doppler imaging can be used for quantitative microflow diagnosis; in the presented study, maps of the first-order moment of the Doppler frequency shift are used as a quantitative and directional estimator of the Doppler signature of particles velocity
The quantitative analysis of transonic flows by holographic interferometry
This thesis explores the feasibility of routine transonic flow analysis by holographic interferometry. Holography is potentially an important quantitative flow diagnostic, because whole-field data is acquired non-intrusively without the use of particle seeding.
Holographic recording geometries are assessed and an image plane specular illumination configuration is shown to reduce speckle noise and maximise the depth-of-field of the reconstructed images. Initially, a NACA 0012 aerofoil is wind tunnel tested to investigate the analysis of two-dimensional flows. A method is developed for extracting whole-field density data from the reconstructed interferograms. Fringe analysis errors axe quantified using a combination of experimental and computer generated imagery. The results are compared quantitatively with a laminar boundary layer Navier-Stokes computational fluid dynamics (CFD) prediction. Agreement of the data is excellent, except in the separated wake where the experimental boundary layer has undergone turbulent transition.
A second wind tunnel test, on a cone-cylinder model, demonstrates the feasibility of recording multi-directional interferometric projections using holographic optical elements (HOE’s). The prototype system is highly compact and combines the versatility of diffractive elements with the efficiency of refractive components. The processed interferograms are compared to an integrated Euler CFD prediction and it is shown that the experimental shock cone is elliptical due to flow confinement.
Tomographic reconstruction algorithms are reviewed for analysing density projections of a three-dimensional flow. Algebraic reconstruction methods are studied in greater detail, because they produce accurate results when the data is ill-posed. The performance of these algorithms is assessed using CFD input data and it is shown that a reconstruction accuracy of approximately 1% may be obtained when sixteen projections are recorded over a viewing angle of ±58°. The effect of noise on the data is also quantified and methods are suggested for visualising and reconstructing obstructed flow regions
Atom Interferometers
Interference with atomic and molecular matter waves is a rich branch of
atomic physics and quantum optics. It started with atom diffraction from
crystal surfaces and the separated oscillatory fields technique used in atomic
clocks. Atom interferometry is now reaching maturity as a powerful art with
many applications in modern science. In this review we first describe the basic
tools for coherent atom optics including diffraction by nanostructures and
laser light, three-grating interferometers, and double wells on AtomChips. Then
we review scientific advances in a broad range of fields that have resulted
from the application of atom interferometers. These are grouped in three
categories: (1) fundamental quantum science, (2) precision metrology and (3)
atomic and molecular physics. Although some experiments with Bose Einstein
condensates are included, the focus of the review is on linear matter wave
optics, i.e. phenomena where each single atom interferes with itself.Comment: submitted to Reviews of Modern Physic
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