Deviation from the Lambert-Beer Law in the Transmittance of a Light Beam Through Diffusing Media: Experimental Results

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Abstract
Attenuation measurements of an He-Ne laser beam in suspensions of polystyrene latex spheres are presented. Measurements were performed with a transmissometer having a receiver with a variable field of view (FOV) in a lenspinhole geometry. Attenuation measurements taken with different fields of view for any fixed optical depth, enabled us to separate the scattered received power P s and the beam-attenuated power P 0 from the total received power P. In this way the true value τ of the optical depth was obtained from P 0 and compared with the apparent optical depth τA obtained from P. Thus the error ∊ = (τ − τA)/τ due to the contribution of scattered received power in attenuation measurements was investigated. Many measurements were taken in order to see how τA and ∊ vary with the optical depth, with the size of the diffusing spheres and with geometric arrangement (radius and angular FOV of the receiver, distance between scattering cell and receiver).