Mapping of airborne ultrasonic fields using optical heterodyne probing and tomography reconstruction

The application of an acousto-optic method to the measurement of airborne ultrasound is described. The method consists of an optical heterodyne interferometric probing of the pressure field emitted by a transducer combined with tomographic algorithm. The method is very sensitive in air (2 10^-4 Pa / √Hz). The measurements of the ultrasonic fields are improved by screening the sound path from the surrounding to prevent from air disturbation. The temperature is measured to compensate velocity variations. Moreover, direct measurements in the cross-section are in good agreement with forward projections, using an inhomogeneous plane waves