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Published August 1, 2001 | Published
Journal Article Open

Mechanisms of ultrasonic modulation of multiply scattered coherent light: a Monte Carlo model


A Monte Carlo model of the ultrasonic modulation of multiply scattered coherent light in scattering media is provided. The model is based on two mechanisms: the ultrasonic modulation of the index of refraction, which causes a modulation of the optical path lengths between consecutive scattering events, and the ultrasonic modulation of the displacements of scatterers, which causes a modulation of optical path lengths with each scattering event. Multiply scattered light accumulates modulated optical path lengths along its path. Consequently, the intensity of the speckles that are formed by the multiply scattered light is modulated. The contribution from the index of refraction is comparable with the contribution from displacement when the acoustic-wave vector is less than a critical fraction of the transport mean free path and becomes increasingly greater than the contribution from displacement beyond this critical point. This Monte Carlo model agrees well with an independent analytical model for isotropically scattering media. Both mechanisms are coherent phenomena, requiring the use of a coherent light source.

Additional Information

© 2001 Optical Society of America. Received February 20, 2001. This project was sponsored in part by National Science Foundation grant BES-9734491, Texas Higher Education Coordinating Board grant 000512-0123-1999, and National Institutes of Health grants R29 CA68562 and R01 CA71980.

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