Non-perturbing measurement of sound pressure fields by means of laser Doppler vibrometer

This paper describes a non-perturbing optical measurement technique (i.e., light refractive tomography) for the reconstruction of sound pressure fields arising from an arbitrarily shaped underwater ultrasound transducer. With this technique, the ultrasound pressure field is measured by a commercial laser Doppler vibrometer (LDV) and reconstructed using the well-developed computed tomography. In the experiment, a cylindrically focused ultrasound transducer excited with 1 MHz burst signal is under investigation. To verify the reliability of this optical technique, a cross section of the pressure field is measured with the optical method as well as hydrophone. The differences between the normalized results of both methods exhibit a maximum of about 10%. Furthermore, we reconstruct the ultrasound pressure field within a volume of about 38 cm³. Without applying any smooth function to the resulting images, the reconstructed pressure field varies continuously in all spatial and temporal dimensions and shows most expected phenomena.