Quantifying the refractive index dispersion of a pigmented biological tissue using Jamin-Lebedeff interference microscopy

Jamin-Lebedeff polarizing interference microscopy is a classical method for determining the refractive index and thickness of transparent tissues. Here, we extend the application of this method to pigmented, absorbing biological tissues, based on a theoretical derivation using Jones calculus. This novel method is applied to the wings of the American Rubyspot damselfly, Hetaerina americana. The membranes in the red-colored parts of the damselfly's wings, with a thickness of similar to 2.5 mu m, contain a pigment with maximal absorption at similar to 490 nm and a peak absorbance coefficient of similar to 0.7 mu m(-1). The high pigment density causes a considerable and anomalous dispersion of the refractive index. This result can be quantitatively understood from the pigment absorbance spectrum by applying the Kramers-Kronig dispersion relations. Measurements of the spectral dependence of the refractive index and the absorption are valuable for gaining quantitative insight into how the material properties of animal tissues influence coloration.