Willemin J F, Dändliker R, Khanna S M
Institut de Microtechnique de l'Université, Neuchâtel, Switzerland.
J Acoust Soc Am. 1988 Feb;83(2):787-95. doi: 10.1121/1.396122.
Conditions in the inner ear for interferometric measurements are quite different from those encountered in other mechanical systems: (i) The inner ear is not mechanically stable, due to blood pulsations and breathing artifacts; (ii) access to the inner ear is limited by anatomical constraints that make it difficult to visualize the structures of interest; (iii) vibration amplitudes to be measured in the inner ear are very low; (iv) the structures in the inner ear are nearly transparent; therefore, the reflectivity is low and attempts to change this reflectivity artificially usually alter the response characteristics; (v) cells are subject to light damage if the incident light intensity is too high, which 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. In contrast to the homodyne system, 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 to the animal, thereby providing an unobstructed view of the structure to be measured. It has a high linearity and dynamic range. Its vibration sensitivity is high (2.8 X 10(-13) m for 1-Hz bandwidth) even under the condition of low light reflectivity (0.02%), with 0.5-mW incident laser power.
（i）由于血液脉动和呼吸伪影，内耳在机械上不稳定；（ii）进入内耳受到解剖学限制，使得难以可视化感兴趣的结构；（iii）内耳中要测量的振动幅度非常低；（iv）内耳中的结构几乎是透明的；因此，反射率很低，并且人为改变这种反射率的尝试通常会改变响应特性；（v）如果入射光强度过高，细胞会受到光损伤，这限制了可在干涉仪中使用的激光功率。描述了一种专门设计用于测量活体内耳振动的外差干涉仪。详细讨论了该仪器的理论和实验特性。与零差系统相比，该干涉仪的测量精度不受低频动物运动的影响。该系统不需要将参考镜附着在动物身上，从而提供了对要测量结构的无阻碍视图。它具有高线性度和动态范围。即使在低光反射率（0.02%）的情况下，其振动灵敏度也很高（1赫兹带宽下为2.8×10^(-13)米），入射激光功率为0.5毫瓦。
