OPTICAL MEASUREMENT OF PIEZOELECTRIC CONSTANTS USING A HETERODYNE INTERFEROMETRIC PROBE

Piezoelectric constants of crystals (SiO2, LiNbO3) and polymers (PVDF) have been determined using an optical heterodyne interferometer to measure the strain. With this set-up, the minimum detectable displacement is 10(-3) angstrom and the accuracy is 5%. The effect of the bonding to the support has been analysed and experimentally checked. The well established value of modulus d11 of quartz (2.31 x 10(-12) m/V) has been confirmed. For LiNbO3 the controversial value of d33 was determined as 9.5 x 10(-12) m/V. For PVDF, the method leads to a constant d33 (13.6 x 10(-12) m/V) more than two times smaller than the figure given by the manufacturer.