Diffraction of light by the cuticle structure of hair.

Under a microscope, hair looks like a surface relief grating with an irregular sawtooth profile. Using scalar diffraction theory, we model what has been, until now, assumed to be a specular peak in the light scattering data. Diffraction efficiencies are calculated as a function of cuticle thickness. Convolution with apertures and Gaussian processes yields a picture that is consistent with the observed position and structure of the "specular" peak. When the cuticle thickness fails to satisfy the blaze condition, the scattered light is distributed amongst multiple diffraction orders giving rise to a complex central structure.