Optical and electrical characterization of natural and synthetic melanin

The optical properties of natural and synthetic melanin have been characterized for a number of laser wavelengths in the visible region. Natural melanin was prepared from hydrolyzed melanosomes isolated from normal, bovine retinal pigment epithelium. The inverse adding doubling method based on the diffusion approximation and radiative transport theory was employed to determine the absorption, scattering, and scattering anisotropy coefficients of melanin from the measurements of diffuse transmission, diffuse reflection and collimated transmission using double integrating spheres. The results obtained by the use of the inverse adding doubling method were compared to the Monte Carlo simulation technique. Characterization of melanin is now being extended to include electrical photoconductivity of melanin thin films on a semiconductor substrate.