Effects of a modulation of the pump-polarization in a degenerate pump/probe experiment

The effects of the pump-polarization in a degenerate pump/probe experiment are analyzed. It is shown that modulating the pump polarization from linear to circular induces a modulation in the probe absorption change that allows to separate various contributions that are mixed in the signal. An experimental demonstration is carried out in a laser dye (Coumarin 500)

Origin of the resonant optical Kerr nonlinearity in Cd(S, Se)-doped glasses and related topics

International audienc

Evolution of the Skin Microstructural Organization During a Mechanical Assay

International audienceSkin is a complex multi-layered tissue, consisting of three main parts: the epidermis, the dermis and the hypodermis. The dermis is responsible for most of the complex mechanical properties of skin, such as viscoelasticity, non-linearity and anisotropy. At the microscopic level the dermis consists for the greater part of extracellular matrix, compounded mainly of collagen fibers forming an orderless network. The mechanical properties of skin have been studied in the past, but their exact link with the microscopic organization is still an open question. The goal of our study is to measure the evolution of the microstructure during a mechanical assay and to improve existing mechanical models of skin with relevant parameters identified at the microscopic level.We perform uniaxial tensile test on ex vivo mouse skin. The mechanical tests are performed in situ under a second harmonic generation microscope. This allows us to determine quantitatively and simultaneously the mechanical response and the microstructural reorganization of the tissue. This technique can be used to better understand the link between pathological alterations of collagen synthesis, fibers organization, and alteration of the biomechanical properties of skin, as in the Ehlers-Danlos syndrome (EDS)

Imaging and 3D morphological analysis of collagen fibrils

The recent booming of multiphoton imaging of collagen fibrils by means of second harmonic generation microscopy generates the need for the development and automation of quantitative methods for image analysis. Standard approaches sequentially analyse two-dimensional (2D) slices to gain knowledge on the spatial arrangement and dimension of the fibrils, whereas the reconstructed three-dimensional (3D) image yields better information about these characteristics. In this work, a 3D analysis method is proposed for second harmonic generation images of collagen fibrils, based on a recently developed 3D fibre quantification method. This analysis uses operators from mathematical morphology. The fibril structure is scanned with a directional distance transform. Inertia moments of the directional distances yield the main fibre orientation, corresponding to the main inertia axis. The collaboration of directional distances and fibre orientation delivers a geometrical estimate of the fibre radius. The results include local maps as well as global distribution of orientation and radius of the fibrils over the 3D image. They also bring a segmentation of the image into foreground and background, as well as a classification of the foreground pixels into the preferred orientations. This accurate determination of the spatial arrangement of the fibrils within a 3D data set will be most relevant in biomedical applications. It brings the possibility to monitor remodelling of collagen tissues upon a variety of injuries and to guide tissues engineering because biomimetic 3D organizations and density are requested for better integration of implants