A self-mixing laser-diode interferometer for measuring basilar membrane vibrations without opening the cochlea.
A laser-diode forms the basis of a displacement sensitive homodyne interferometer suitable for measurements from poorly reflective surfaces. The compact and cost-effective interferometer utilizes the self-mixing effect when laser light reflected from a moving target re-enters the laser cavity and causes phase dependent changes of the lasing intensity. A piezo positioner was used to displace the interferometer with known frequency and amplitude as a basis for real-time calibration of the interferometer's sensitivity. The signal-processing algorithm is described that allows measurements in presence of high amplitude noise leading to variation of the interferometer's operating point. Measurements of sound-induced basilar membrane displacements were made in the intact cochleae of rodents by focusing the laser beam of the interferometer through the transparent round window membrane. The interferometer provides a viable means for making subnanometre mechanical measurements from structures in the inner ears of small mammals, where opening of the cochlea is not practicable.
School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK. a.lukashkin@sussex.ac.uk
Andrei N
AN
Lukashkin
Mikhail E
ME
Bashtanov
Ian J
IJ
Russell
D000465:Algorithms; D000818:Animals; D001489:Basilar Membrane / Q000033:anatomy & histology / Q000502:physiology*; D004432:Ear, Middle / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery; D006168:Guinea Pigs; D006309:Hearing / Q000502:physiology*; D007368:Interferometry / Q000295:instrumentation / Q000379:methods*; D007834:Lasers / Q000592:standards*; D009925:Organ of Corti / Q000502:physiology; D012405:Round Window, Ear / Q000033:anatomy & histology / Q000502:physiology* / Q000601:surgery*; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation; D014732:Vibration