Generic model of the molecular orientational distribution probed by polarization-resolved second-harmonic generation

Abstract

International audienceIn this work we investigate a generic method able to extract information on molecular organization in biological samples from polarized second harmonic generation (SHG) microscopy, without the need to infer an a priori model for the molecular orientational distribution. The mean orientation of this distribution, as well as its first and third orders of symmetry, are estimated by monitoring SHG intensity signals under a varying incident polarization. We introduce, in particular, a reduction of the problem to a two-dimensional approach appropriate to the microscopy geometry. This method allows us to retrieve determining information which is not available in the traditional model-oriented methods, as illustrated in molecular-order imaging in collagen fibrils. The precision of the parameters estimation is evaluated by a Monte Carlo analysis, based on the Poisson noise statistics of the measured signal

Precise, motion-free polarization control in Second Harmonic Generation microscopy using a liquid crystal modulator in the infinity space

“…Moreover, adding a quarter wave plate or LCM in the collection pathway, we can determine the Mueller matrix of the tissue for further characterization [38]. We note that the analysis here was performed for well-aligned tissues by averaging over the field of view, the instrumentation is also applicable to perform pixelbased analysis for more complex morphologies such as that recently presented by Brasselet and associates [39].…”

Microscopic structural study of collagen aging in isolated fibrils using polarized second harmonic generation

“…The so-called order parameters (p 1 ; p 3 ; q 3 ) are deduced from the normalized Fourier coefficients (a 2 ∕a 0 ; · · · ; b 4 ∕a 0 ) by minimizing the mean square error between experimental coefficients and theoretical predictions. 16 The quantity p ¼ p 3 ∕p 1 is used as an indicator of molecular order, while q 3 indicates an asymmetry of the distribution. 16 This model is general and does not require an a priori known molecular distribution to quantify molecular order.…”

“…16 In this generic approach, nonlinear active molecules of collagen fibrils are considered to lie within a molecular distribution function which can be reduced to a 2-D function:…”

Imaging the Nonlinear Susceptibility Tensor of Collagen by Nonlinear Optical Stokes Ellipsometry

“…Two angles (the in-plane azimuthal rotation angle f and out-of-plane polar tilt-angle q) are recovered in the analysis. The recovery of the orientation information of collagen has been one of the overall goals of polarization-dependent SHG measurements (28). The influence of q on the polarization-dependent nonlinear optical measurements has been explored and discussed qualitatively (29).…”