Michelson interferometer for the piezoelectric coefficient measurements

The present work has described the Michelson interferometer which is capable of measuring the vibrational amplitudes in a sub-angstrom range. In the system, a He-Ne laser is used as a monochromatic source of light and a photodiode as a detector to convert an optical signal into an electronic one. Lock-in detections of the electronic signals are applied to relate the vibrational amplitudes to the wavelength of the laser beam. A feedback circuit is introduced in order to stabilize the sensitivity of the interferometric system. With this setup, a mechanical displacement referred to a change in thickness of a vibrating sample can be measured and the corresponding piezoelectric coefficient, i.e. the ratio of the change in sample thickness to the applied voltage, evaluated. In order to check the performance of the system, measurements on lithium niobate (LiNbO3) have been made and its piezoelectric coefficient d33 was confirmed with 2% accuracy. The piezoelectric coefficient d33 for lead zirconate titanate (PZT) ceramics was, therefore, determined by this interferometer and found to be 270 pm/V