Scanning Double-Beam Laser Interferometer with Loop-Back Compensation and Phase Stabilization

An accurate characterization of piezoelectric films is essential for their usage in various types of MEMS sensors and actuators. This paper presents a novel scanning double-beam laser interferometer (DBLI) to measure the thickness piezoelectric coefficient with a high accuracy. Compared to previous DBLI solutions, we employ a closed-loop phase shift compensation via an electro-optical modulator to stabilize the random phase drift as well as to compensate the harmonic sample-induced phase shift. As a consequence, the setup robustness is enhanced and the measured displacement is no more sensitive to sample reflectivity or source and detector signal gains, which allows to use the DBLI as scanning.