Piotr Kwiek

Diffraction of light by adjacent fundamental and second or fourth harmonic ultrasound beams: Comparison of exact and simplified formulae with experiment

Abstract Theoretical expressions and their approximate formulae for the intensities of light diffracted by two adjacent ultrasonic beams are discussed and compared with experimental data for the case when the second beam is an even harmonic of the first (fundamental). In the special case of the fundamental and its second or fourth harmonic, relatively simple formulae are found for the first and second diffraction orders describing the variation of light intensity with phase shift and intensity ratio. The approximate formulae describe the experiments satisfactorily only for small values of ζ 1 and α n . For higher values the exact formulae give better agreement. Only the Raman-Nath region is considered.

Determination of the Klein-Cook parameter in ultrasound light diffraction

For weak and strong acousto-optic interaction analytical solutions are available which describe the diffraction problem. In the intermediate range between these limiting cases, however, the light-sound interaction is far more difficult to analyze for two reasons: (i) Only numerical approaches are available and (ii) the diffraction problem depends on two parameters: the Raman-Nath parameter and the Klein-Cook parameter. This paper describes a technique which makes possible the determination of the Klein-Cook parameter with an adequate accuracy for many fields of application. Once the Klein-Cook parameter is known, the Raman-Nath parameter can easily be obtained from numerical approaches.

Uncertainty considerations of ultrasonic field mapping by light-diffraction tomography

Ultrasound light diffraction in conjunction with a computer-tomographic evaluation procedure allows ultrasonic fields to be mapped as long as the limits of weak acousto-optic interaction are not exceeded. Beyond these limits, the light-sound interaction is far more complex, and the simplified evaluation based on the Raman-Nath approach will give rise to considerable errors. Two typical idealized sound beam configurations, of a circular and a square sound column, are used for numerically treating the problem. It could be shown that, depending on the light-sound interaction length and the ultrasound frequency, errors of the order of 50% are not rare.

Acousto-optic interaction of a Gaussian laser beam with an ultrasonic wave of cylindrical symmetry

We present experimental studies of the interaction between a narrow Gaussian laser beam and a standing cylindrical ultrasonic wave. As a theoretical approach, a Fourier-optics-based successive diffraction model is used. Depending on the ratio of the Gaussian laser beam diameter to the first nodal diameter of the cylindrical ultrasound, light refraction or diffraction is observed. We experimentally investigate the time-averaged light intensity as well as the modulation of light in the far field of light refraction-diffraction by a cylindrical ultrasound. It is revealed that significant focusing appears if the phase front of the incident light is curved. The focusing effects of the acousto-optic system depend on the width of the laser beam and curvature of the phase front. Finally, possible applications are discussed.

On ultrasound light diffraction

Abstract Light diffraction by ultrasound waves is discussed over the wide range from weak acousto-optic interaction to strong acousto-optic interaction, in terms of numerical simulations and experimental investigations for normal incidence. Particular emphasis has been placed on the complex nature of the diffracted light amplitude. The paper is intended as a contribution towards a unified representation of the general phenomenon.

An arrangement for ultrasound field measurements using optical holography

Abstract A description of methods and the arrangement for the experimental study of an ultrasonic field and displacements of piezoelectric transducer distribution using optical holography is presented. As an example of the experimental possibilities some photographs are given of reconstructed holograms obtained with the pulse (stroboscopic) double-exposure and the averaged-in-time methods.

Optical mapping of ultrasonic fields in the intermediate range between weak and strong acousto-optical interaction

Weak acousto-optical interaction provided, light diffraction tomography has proved to be a useful tool for mapping ultrasonic fields. Beyond this range, data acquisition and evaluation is far more difficult, which is mainly due to the fact that, in this case, the light intensity is no longer a function of only one variable but of two. Furthermore, the measurement of the acoustic phase is affected by additional optical phase shifts. A method has been developed which facilitates the quantitative mapping of ultrasonic fields in the intermediate range between weak and strong acousto-optical interaction. In terms of the ultrasonic frequency and the light sound interaction length, the measurement range could be extended by more than one order of magnitude. As a result, the favourable properties of light diffraction tomography, e.g. data acquisition without retroaction and with high spatial resolution, can be utilized for sound field investigations which have not been possible so far.

Optical mapping of ultrasonic fields using Bragg incidence

Abstract Weak acousto-optical interaction and normal light incidence provided, light diffraction tomography has proved to be a useful tool for mapping ultrasonic fields. Beyond this range, for normal incidence, data acquisition and evaluation has turned out to be far more difficult, which is mainly due to the fact that in this case the light intensity is no longer a function of only one variable but of two. Furthermore, the measurement of the acoustic phase is affected by additional optical phase shifts. A method has been developed which facilitates, by means of Bragg incidence, the quantitative mapping of ultrasonic fields beyond the range of weak acousto-optical interaction. The awkwardness of data acquisition at normal incidence could be avoided. As a result, the favourable properties of light diffraction tomography, e.g. the mapping of ultrasonic fields without retroaction and with high spatial resolution, can be utilized in a frequency range which has not been accessible so far. This in turn might open new perspectives for the calibration of hydrophones in an extended frequency range up to about 50 MHz.

Ultrasound field mapping by light-diffraction tomography: a review

Light-diffraction tomography is a noninvasive measurement technique for mapping ultrasound fields and provides a high spatial resolution. In the range of the Raman-Nath approach, this technique can be successfully applied to frequencies of approximately 5 MHz to ultrasound fields of any geometry. Beyond this frequency range, however, light diffraction implies peculiarities that strongly affect data acquisition. It is the aim of this review to outline the capability of the method, including its range of applicability, and to discuss new steps for its extension.

On the polarization of light diffracted by ultrasound

If light is diffracted by ultrasound in an isotropic medium with acoustically induced birefringence, the state of polarization is modified in each order of diffraction with respect to the initial state of polarization of the incident light wave. In the present paper, some polarization effects are discussed in the case of normal light incidence. In general a rotation of the main polarization plane occurs, together with a change of the ellipticity. However, while the former effect always takes place, the latter only occurs in the case of ultrasonic light diffraction of the intermediate type. Some experimental measurements are included in case of argon laser light being diffracted by an ultrasonic wave propagating in fused silica (SiO2).