Optical absorption, scattering, and multiple scattering: Experimental measurements using food coloring, India ink, and milk

Abstract

A series of optical experiments is used to illustrate color effects, absorption, and scattering. In the simple experiments, the intensity of red laser light is measured after the beam passes through samples with increasing concentrations of food dyes, black ink, and milk. The data are fitted with exponential functions, and similar attenuation is obtained with samples which are very different: black ink and white milk. Measured intensities and visual observations serve to illustrate the distinction between absorption, scattering, and attenuation. In more advanced experiments, attenuation coefficients and the mean attenuation length are measured. With milk samples, intensity measurements reveal a non-exponential concentration dependence which is a signature of multiple scattering. Finally, intensity as a function of distance is measured by scanning wedge-shaped samples of ink or milk across a detector. The effects of multiple scattering in milk are very pronounced in this case.