Optical characterization of nacre using hyperspectral imaging

Nacre is an organic-inorganic biomineral that lines the inside of shells of various species of mollusks, and comprises layers of aragonite tablets with thicknesses on the order of hundreds of nanometers, bound by an organic protein. The iridescent appearance of nacre results from thin-film interference effects within this layered structure, even though the layers are quite inhomogeneous due to surface roughness, shell curvature, and the disordered nature of the tablets comprising the aragonite layers.

The average thickness (and variance) of the nacre layers can encode information, for example the ocean temparture at the time of formation. However, obtaining information about the layer thickness typically requires destructive methods involving preparing and imaging cross-sections, and can require many cross-sections to map an entire sample.

Here, we present a method that combines polarized hyperspectral imaging with thin-film modeling, that is capable of nondestructively mapping the thickness of nacre layers across an entire specimen.

This work was performed together with Jad Salman, Alireza Shahsafi, Chang-Yu Sun, Steve Weibel, Chris Draves, Michel Frising, Brad Gundlach, Yuzhe Xiao, Gabor Kemeny, and Pupa Gilbert.