In vivo spectroscopic ellipsometry measurements on human skin.

We study the behavior of optical properties of human skin across its layers. We describe ellipsometric measurements for spectrally resolved in vivo investigations of biological tissue. We show in vivo measurements on human skin of the ellipsometric parameters Psi and Delta, which describe the change in polarization of light on reflection on a sample. A tape-stripping study reveals the depth profile of the ellipsometric parameters into the stratum corneum. The depth profile shows an increase in both quantities with increased depth. Analyzing the development of Psi on the number of strips using an exponential function shows a steady state after approximately 2 microm. The evolution of Psi and Delta can be described using a morphological model containing an effective medium approximation accounting for the water content of the skin, surface roughnesses of the corneocytes, as well as the alternating cell and lipid layers.