Scattering optics of foam

The multiple scattering of light by aqueous foams is systematically studied as a function of wavelength, bubble size, and liquid fraction. Results are analyzed in terms of the transport mean free path of the photons and an ex trapolation length ratio for the diffuse photon concentration field. The wa velength dependence is minimal and may be attributed entirely to the wavele ngth dependence of the refractive index of water rather than thin-film inte rference effects. The transport mean free path is found to be proportional to the bubble diameter and the reciprocal of the square root of liquid frac tion. The extrapolation length ratio varies almost linearly with liquid fra ction between the values for water- glass-air and air- glass-air interfaces . (C) 2001 Optical Society of America.