We report high-precision measurements of the absorption and the reduced scattering coefficients for turbid media. Using a frequency-domain measurement technique for a point-source infinite-medium geometry, we find that the standard deviations of multiple measurements of the absorption coefficient and the reduced scattering coefficient are less than 0.6%, and three independently derived values for and agree to better than 1%. Measurements of agree with measurements of a nonscattering medium to within 1.2%. To obtain high precision requires attention to proper conditions for the spherical photon-density wave model, the detection linearity, and the ratio of the absorption rate to the source modulation rate. Frequency-domain amplitude and phase measurements deviate from fitted curves by 0.1% and 0.06° rms, respectively.
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