Absolute Measurement of Surface-Vibration-Patterns in Piezoelectric Devices Using Two Lasers with Different Wavelengths

Our new method solves the limitation of the previous measurement system for in-plane vibration displacement, using two semiconductor lasers with adequately separated wavelengths. Different gammas, that is, interference factors, are determined for each speckle image by using lasers with different wavelengths. The ratio of the two gammas is proportional to the reciprocal of the wavelength ratio of the lasers. The distributions of the absolute vibration displacement can be mapped based on this relationship and statistical processing of the speckle images. A red laser and a violet laser were used in the actual measurement system. A 23-MHz circular AT-cut quartz resonator was used to test the validity of our method, and the results are compared here to the results previously obtained by the two-drive-level burst wave excitation method. Our experiments showed good agreement between the two displacements, thereby validating the proposed method.