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Communication Dans Un Congrès Année : 2010

Imaging of a Crack by Nonlinear Frequency-Mixing Photoacoustics: Theory

Résumé

One-dimensional theory of the nonlinear frequency-mixing photoacoustic crack imaging is developed. This imaging can be realized through the excitation of the crack by two laser beams independently modulated in intensity at two very different frequencies and the detection of the components of photoacoustic spectrum at mixed frequencies. It is predicted that the high contrast of this imaging can be caused by strong dependence of the efficiency of optoacoustic conversion on the mechanical state of the crack, i.e. on whether the crack is open or is at least partially closed due to the contacts between the crack faces. The theory relates earlier experimental observation of the large number of the mixed frequencies [1] to strong bimodular nonlinearity of the crack. In response to sinusoidal modulation of pump laser intensity at low frequency the rigidity of the crack varies in a strongly non-sinusoidal manner through abrupt jumps between its value corresponding to an open soft state of the crack and its value corresponding to a much more rigid closed state of the crack. Parametric interaction of the acoustic waves generated by probe laser radiation harmonically modulated in intensity at high frequency with this strongly non-sinusoidal motion excites multiple side-lobes around the high frequency. The theory indicates that information on the crack rigidity could be obtained from the measurements of optoacoustic conversion efficiency and that the information on the parameters of the dependence of the crack width on the applied force can be obtained from the measurements of the dependence of the side-lobes spectrum on the pump laser intensity. [1] N. Chigarev, J. Zakrzevskii, V. Tournat and V. Gusev, Nonlinear frequency-mixing photoacoustic imaging of a crack. J. Appl. Phys. 106, 036101 (2009).
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Dates et versions

hal-00549191 , version 1 (21-12-2010)

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  • HAL Id : hal-00549191 , version 1

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Vitali Goussev, Nikolay Chigarev. Imaging of a Crack by Nonlinear Frequency-Mixing Photoacoustics: Theory. 10ème Congrès Français d'Acoustique, Apr 2010, Lyon, France. ⟨hal-00549191⟩
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