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.
Lukashkin
Andrei N
AN
School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK. a.lukashkin@sussex.ac.uk
Bashtanov
Mikhail E
ME
Russell
Ian J
IJ
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