Vibration amplitude range enhancement method for a heterodyne interferometer

Scanning heterodyne interferometers are widely used in micro-vibration measurements due to its high sensitivity and high resistivity to environment change. However, the amplitude range of scanning heterodyne interferometers is limited by the approximation in the theory to several nanometers. To solve this problem, a method for vibration amplitude range enhancement is proposed. By exploiting the Bessel functions, the interferometer is able to measure vibration amplitude ranging up to several hundred nanometers. The method was validated by measuring a micro-cantilever and the results were desirable. To further demonstrate the method, measurements were performed on a piezoelectric micromachined ultrasonic transducer (PMUT) with the maximum amplitude up to similar to 300 nm.