Heterodyne laser speckle imaging enabling kHz mechanical vibration mapping using a lower frame rate camera

Laser speckle-based vibrometry offers simplicity and ease of alignment for spatial vibration measurement; however, its detection range is limited by the camera speed. We propose a simple optical method for detecting high-frequency vibrations by illuminating the vibrating surface with periodically modulated laser light tuned close to the vibration frequency. The resulting heterodyned speckle signal is captured by a camera, which records slowly varying signal components that encode vibration information. This information is then extracted and visualized using a vibration mapping algorithm. Theoretical and experimental analyses demonstrate vibration-mapping capabilities in the kilohertz range, even with a 200 Hz camera.