Pulse wave scattering by an absorber and integrated attenuation in the diffusion approximation

The diffusion equation derived from the space-time transport equation, in contrast to the conventional diffusion equation, should have a diffusion coefficient perfectly independent of the attenuation coefficient, gamma(ab), without any constraint on the magnitude of gamma(ab) and also on its possible spatial inhomogeneity; however, in the case of time-independent diffusion equations, including those for,intensity-modulated density waves, such parameters are subjected to constraints including both gamma(ab) and the modulation frequency. Basic equations for a fixed scatterer embedded in the random medium are presented with reference to previous papers, with some applications. A previous expression for integrated attenuation in a slowly changing medium of gamma(ab) is improved to be valid to second order of gamma(ab) for a temporal pulse wave and to first order for an intensity-modulated wave. (C) 1997 Optical Society of America.