Optical phase contrast mapping of highly focused ultrasonic fields

The most common method of measuring an ultrasonic pressure field is a hydrophone scan. However, this method has a long scanning time and disturbs the acoustic field. In this study, we used an optical phase contrast method for the measurement. Because this method uses light, fast and noninvasive measurement can be performed. The projections of an ultrasonic pressure field were obtained with a charge-coupled device (CCD) camera, and the three-dimensional (3D) acoustic pressure field was reconstructed using a computed tomography (CT) algorithm from these projections. The result was compared with that of hydrophone measurement and demonstrated the successful reconstruction of a focal ultrasonic pressure field.