Imaging acoustic phenomena with transmission electronic speckle pattern interferometry

Optically imaging acoustic phenomena requires sensing the pressure-induced change in index of refraction of the medium, and imaging this change in index has been accomplished in the past using a variety of methods. However, these methods typically require a static ambient atmosphere, the sensing area is often limited by the size of the optics, and in some cases the phenomena of interest must be either reproducible or stable for time periods exceeding tens of minutes. We demonstrate that transmission electronic speckle pattern interferometry (TESPI) is a fast and effective method for imaging gas flow, acoustic standing waves, and standing waves in the presence of flow, with sensing times of less than one second and a viewing area of a square meter or more. [Work supported by NSF grant No. PHY–2109932.]