Vibration of low amplitude imaged in amplitude and phase by sideband versus carrier correlation digital holography

TL;DR

This paper introduces a method using sideband digital holography to image and measure very low amplitude vibrations by correlating fields at different frequencies, achieving high sensitivity and noise reduction.

Contribution

It proposes recording and correlating the carrier and sideband fields sequentially to directly measure mechanical motion phase, improving vibration detection sensitivity.

Findings

Detected vibrations as low as 0.01 nm at 2 kHz

Correlation method is insensitive to surface roughness phase

Averaging over neighboring pixels enhances signal-to-noise ratio

Abstract

Sideband holography can be used to get fields images (E0 and E1) of a vibrating object for both the carrier (E0) and the sideband (E1) frequency with respect to vibration. We propose here to record E0 and E1 sequentially, and to image the correlation E1E * 0 . We show that this correlation is insensitive the phase related to the object roughness and directly reflect the phase of the mechanical motion. The signal to noise can be improved by averaging the correlation over neighbor pixel. Experimental validation is made with vibrating cube of wood and with a clarinet reed. At 2 kHz, vibrations of amplitude down to 0.01 nm are detected.