Optical visualization of ultrasound pressure fields in turbid media based on coherent detection imaging technique

An optical method for visualizing ultrasound fields in turbid media is described. A laser beam is modulated by ultrasound waves in a light-scattering medium and is detected using a coherent detection imaging technique based on the optical heterodyne method. We demonstrate for the first time the ability to visualize the profile of an ultrasound field generated by a focus-type ultrasound transducer. This is achieved by utilizing forward-scattered light originating from a laser beam that is phase modulated by Raman-Nath diffraction and is also modulated in amplitude through the density variation of scatters in a test medium and/or a small amount of beam deflection. In this Study, we demonstrate the two-dimensional determination of a sound field, even in an optically turbid medium.