FIBER-OPTIC VIBRATION MEASUREMENT FOR LOW REFRACTIVE-INDEX MEDIA USING WAVEFRONT SPLITTING INTERFEROMETRY

A fiber-optic vibration measurement technique based on the wavefront-splitting interferometry is presented in this paper. Due to a small divergence angle of Gaussian laser beam emitting from a single-mode fiber, the sensing beam propagating toward the specimen has an incident angle of nearly 90 degrees, so that the reflection coefficient of specimen surface is relatively high even for low-refractive-index materials. In preliminary tests, overhead-projector transparency was used to demonstrate the vibration measurement with our fiber-optic vibration sensor up to 4 kHz. The Young's modulus of the transparency was also determined by using the vibration method, and the result agreed well with that measured by using a conventional testing machine.