Light refractive tomography is an optical measurement technique that is able to provide absolute sound pressure values in specified volumes. Because of the simplicity of the measurement principle as well as the compactness of the measurement setup, light refractive tomography offers higher measurement performance and fewer error sources than light diffraction tomography. In this contribution, a numerically simulated ultrasound pressure field is exploited to determine the experimental parameters and to analyze the error sources as well as their influences on final results. After that, several ultrasound transducers excited with 1 MHz signals are investigated. The light refractive tomography results show good agreement with hydrophone measurements. Finally, we reconstruct 2000 transient states of the ultrasound pressure field within a volume of about 38 cm(3) after sending the burst signal. Without applying any smoothing to the resulting images, the reconstructed pressure field varies continuously in both spatial and temporal dimensions.

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In this paper we present a super-resolving approach for detecting an axially moving target that is based upon a time-multiplexing concept and that overcomes the diffraction limit set by the optics of an imaging camera by a priori knowledge of the high-resolution background in front of which the target is moving. As the movement trajectory is axial, the approach can be applied to targets that are approaching or moving away from the camera. By recording a set of low-resolution images at different target axial positions, the super-resolving algorithm weights each image by demultiplexing them using the high-resolution background image and provides a super-resolved image of the target. Theoretical analyses as well as simulations and preliminary experimental validation are presented to validate the proposed approach.

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This paper describes an optical measurement technique, referred to as light refractive tomography (LRT), which enables noninvasive measurement of ultrasound pressure fields in water. The pressure field arising from a cylindrically focused ultrasound transducer is measured separately by means of LRT and hydrophone. Good agreement is achieved between the results obtained by these two different methods. After that, LRT is extended and applied to the reconstruction of density variations in a PMMA block induced by ultrasound. The results appear plausible, however, a quantitative verification is currently still missing, since we know of no other published methods succeeding so far in the measurement of density change in solids induced by ultrasound.