On the effect of the width of the scattering indicatrix on the dispersion of photon density waves in a strongly scattering medium

The dispersion of photon density waves in strongly scattering media with different widths of the scattering indicatrix is studied by the spherical harmonics method using approximations of various orders (up to the P7 approximation inclusive). It is shown that, beginning from the P3 approximation, the reduction in the velocity of photon density waves that is characteristic of the P1 approximation is eliminated and, independently of the width of the scattering indicatrix in the region of modulation frequencies exceeding 1010 Hz, the velocity of photon density waves asymptotically approaches the speed of light. Our study of the damping of photon density waves has shown that the formula obtained previously for the calculation of the damping coefficient (Imk(μs′, ω)) as a function of the transport scattering coefficient and the velocity is valid at Imk ≤ μs (μs is the light scattering coefficient). The maximum growth in the damping coefficient of photon density waves with a further increase in the frequency is limited by the value of the light scattering coefficient Imkmax ≈ μs.