Optical analysis of finite-amplitude ultrasonic pulses

Abstract

Finite-amplitude pulses are examined acousto-optically using a newly developed lightdiffraction apparatus. Based on an optical analysis of ultrasonic transducer response to continuous-wave excitation at and near the fundamental frequency, pulse Fourier spectra are derived for input to a light-diffraction model, providing quantitative agreement between experiment and theory. The diffraction theory predicts that a light-diffraction pattern produced by a harmonically distorted acoustic pulse train will exhibit asymmetry in the intensity distribution with respect to the zero order. To simulate harmonic distortion, pulse frequency spectra are used for input to a computational model that is based on the Burgers' equation for propagation of finite-amplitude acoustic waves in a nonlinear medium. The spectrum, propagation, and light-diffraction models give a complete description of light diffraction by finite-amplitude pulses and provide good agreement with experimentally obtained diffraction patterns.

Acousto-optic holography

“…As in conventional NAH, the proposed method describes the studied sound field using harmonic functions with a common phase reference [Eq. (10)] and, therefore, fully coherent sound fields are required. To deal with practical cases in which the sound field is generated by multiple incoherent sources, the procedure should be adjusted.…”

“…8 Techniques based on diffraction are mostly used for the visualization of ultrasound. [9][10][11] In contrast, light deflection is better studied as a geometrical optics problem in which light is described in terms of rays. Light rays deflect (bend) due to the acoustically induced gradient in the medium refractive index.…”

Determination of Radiation Pressure in Acoustic Levitation by Optical Acoustic-Field Measurement

“…The optical phase data associated with a given pixel are the result of changes in the index of refraction along the entire line of sight associated with that pixel. In fact, diffraction due to these index variations can cause further complications, with interference from multiple paths removing this simple pixel-to-line-of-sight correspondence [35]. For the measurement geometry considered here and the relatively long ultrasound wavelength used, the assumption of straight paths through the gas only yields small errors.…”