We measured the effective absorption and reduced scattering coefficients on the surface of two-layered turbid media using a frequency-domain multi-distance method. We measured the amplitude and the phase of the modulated intensity at source-detector distances ranging from 1.5 to 3.0 cm. We considered several combinations of one layer (L) (thickness: 0.1-1.6 cm) placed on top of one block (B) (thickness ~ 5 cm). We found that for layers less than about 0. 40 cm thick the frequency-domain multi-distance method yields the optical properties of the underlying block. We also found that for layers more than 1.3 cm thick the frequency-domain multi-distance method yields a reduced scattering coefficient which reproduces that of the superficial layer. For a layer thickness in the range of 1.31.6 cm, the effective absorption coefficient approaches the layer absorption coefficient but does not match it to within experimental errors.
© 1998 Optical Society of AmericaPDF Article