Low-frequency mechanical artifacts, such as pulse or respiratory movements, cause less distortion of the highfrequency measurement signal and are easier to filter out. Modulating the reference beam with a high frequency (in the MHz range), which is done using a Bragg cell, Kerr cell, or a rotary grating disk, results in an improved signal-to-noise ratio. In contrast with the Michelson interferometer, the reference beam is modulated in its frequency or phase. ![]() These instruments could make measurements in vivo with a high degree of sensitivity. “Heterodyne interferometers” were introduced into otologic research during the 1970s. ![]() 5 Modified Michelson interferometer for measuring tympanic membrane vibrations (after Tonndorf and Khanna, 1968 ).Īnother way to improve the sensitivity of interferometers is by modifying the measurement principle.
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