Heterodyne Interferometer For Submicroscopic Vibration Measurements In The Inner Ear.

J. F. Willemin; S. M. Khanna; R. Dandliker

doi:10.1117/12.939771

10 September 1987 Heterodyne Interferometer For Submicroscopic Vibration Measurements In The Inner Ear.

J. F. Willemin, S. M. Khanna, R. Dandliker

Proceedings Volume 0746, Industrial Laser Interferometry; (1987) https://doi.org/10.1117/12.939771
Event: OE LASE'87 and EO Imaging Symposium, 1987, Los Angeles, CA, United States

Abstract

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.

Citation Download Citation

J. F. Willemin, S. M. Khanna, and R. Dandliker "Heterodyne Interferometer For Submicroscopic Vibration Measurements In The Inner Ear.", Proc. SPIE 0746, Industrial Laser Interferometry, (10 September 1987); https://doi.org/10.1117/12.939771

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