Measurement of high-frequency speckle vibration amplitude from a blurred image

The non-contact detection of a vibrating surface through the extraction of the vibration of the speckle pattern that the surface produces when illuminated by a coherent source of light has been implemented almost from the invention of the laser and is still an active field of research. In this work, the vibration amplitude of a speckle pattern is measured using a single blurred image taken with exposure times that are multiples of the vibration period. The method is based on the variation of the cross-correlation function width as a function of the speckle vibration amplitude. There is no analytical expression for that function, so it must be obtained numerically. The oscillating speckle patterns were produced with a piezoelectric transducer excited at vibration frequencies ranging from a few Hz up to tens of kHz. A custom CMOS photodetector sensor with programmable interconnection between pixels was used to verify the speckle pattern vibration amplitude and frequency.