Measurement of the χ(2)-distribution in poled nonlinear optical polymer films

We present a method for analyzing the homogeneity of the chi((2)) distribution in poled nonlinear optical polymer films. The second order nonlinear coefficient in these polymers is commonly induced by electric field poling methods which can lead to a chi((2)) distribution with poor spatial homogeneity. In this paper, we analyze the chi((2)) distribution using scanning Kelvin microscopy. This allows us to detect the height and the direction of the induced polarization through the probing of the counter charges that are present on the polymer surface. We compare the response to that obtained from the scanning second harmonic microscopy (SSHM) method, in which the direction of the orientation, and thus the phase of chi((2)), can not be seen. We also propose a method to measure the chi((2)) distribution in three dimensions by analyzing the SSHM images obtained at various wavelengths.