Interfering diffusive photon-density waves with an absorbing-fluorescent inhomogeneity

This work reports an investigation of the fluorescent field reemitted by an object embedded in a highly scattering media illuminated by two-interferin g sources. Simulations in the frequency domain with a finite difference met hod solving the diffusion equation were performed. The media considered had features typical of a soft-compressed breast. An absorbing-fluorescent inh omogeneity was embedded in the center of the slab. A qualitative study of t he re-emitted field was achieved. The reemitted field was found to possess unique features characteristic of the two-interfering sources excitation, i .e. null intensity when the object was between the two sources and a 180 de grees transition crossing this position. Those features, when performing a scan of the two sources, permitted accurate localization of the inhomogenei ty. Moreover, even when the detector was not placed on the mid-plane of the two sources, the re-emitted field still exhibited the interfering characte ristic pattern, which was not seen at the excitation wavelength. Thus, for such configurations, the re-emitted field still possessed the specific sens itivity of phased array emission conversely to the excitation wavelength. ( C) 2001 Optical Society of America.