Visual measurement of instable sound field using common-path off-axis digital holography

A common-path off-axis digital holography (DH) using a defocus grating is developed to detect and visualize the sound field information through a single laser beam. Setting the grating outside the Fourier plane, our approach divides the laser beam into the object and reference beams by the grating, in which one of the beams is filtered using a pinhole to create the reference beam, and then yields holograms containing the phase information modulated by the sound. After phase reconstruction, a windowed Fourier filter method is employed to extract the instable sound signal and suppress the background noise. A series of experiments are conducted to demonstrate the validity of the proposed approach.