Search

In-plane as well as out-of-plane displacements and vibrations of objects with diffusely scattering surfaces are measured in real-time. Micro-vibrations with amplitudes down to 1 nm and frequencies up to 10 MHz were analysed at a spatial resolution of 30 μm.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Conditions in the inner ear for interferometric measurements are quite different than those encountered in other mechanical systems. (i) The inner ear is mechanically not stable, due to blood pulsations and breathing artifacts; (ii) access to the inner ear is limited by anatomical constraints making it difficult to visualize the structures of interest; (iii) vibration amplitudes to be measured in the inner ear are very low; (v) the structures in the inner ear are nearly transparent therefore the reflectivity is low, attempts to change this reflectivity artificially usually alters the response characteristics; (vi) cells are subject to light damage if the incident light intensity is too high. This limits the laser power that can be utilized in the interferometer. A heterodyne interferometer specially designed to measure vibrations in the living inner ear is described. Theoretical and experimental characteristics of this instrument are discussed in detail, particularly the noise characteristics which determine the limit of sensitivity. It has been shown that the measurement accuracy of this interferometer is not affected by the low frequency animal movements. This system does not require attachment of a reference mirror on the animal allowing precise determination of the measuring point. It has a high linearity and dynamic range. Its vibration sensitivity is high (3x10-16 m for 1 Hz bandwidth) even under the condition of low light reflectivity (0.02%), with 0.5 mrg incident laser power. Therefore vibrations of nearly transparent membranes and structures can be measured directly.

Note: 231 Reference SAMLAB-ARTICLE-2000-015 Record created on 2009-05-12, modified on 2016-08-08

Accurate fringe interpolation in holographic interferometry requires two-reference-beam holographic recording. Using two reference sources close together, the sensitivity to (angular) misalignement of the hologram is drastically reduced (10° instead of 0.01°). Overlapping of the cross-reconstructions can be tolerated, unless extreme precision and spatial resolution are demanded. Experimental results obtained by video processing of such holograms show an accuracy of better than 1 100 of a fringe. The optical setup becomes nearly as compact and simple as in classical holographic interferometry.

In-plane as well as out-of-plane displacements and vibrations of objects with diffusely scattering surfaces are measured in real time. Microvibrations with amplitudes down to 1 nm and frequencies up to 5 MHz were analyzed at a spatial resolution of 35microm.

Amplitude and phase of both in-plane and out-of-plane vibration components are measured in real time using heterodyne speckle interferometry. Microvibrations with amplitudes down to 1 nm and frequencies up to 5 MHz were analyzed at a spatial resolution of 35 microm. Amplitude and phase measurements were performed with an accuracy of better than 6% and 4 degrees , respectively. This permits complete determination of the mechanical movement of a vibrating surface.