The correlation between polarization modulated near-field optical images and the anisotropy of the probe

The true anisotropic images taken with the polarization modulation near-field optical microscope are often influenced by the linear dichroism of the tapered fibre probe. In this paper, we develop a new method to separate the anisotropic image form probe's dichroism. Our calculations show that the near-field optical image is simply a vector sum of the sample's dichroism and the probe's dichroism, when the probe's anisotropy is small. With this result, we demonstrate the true anisotropic images of poly(phenylene vinylene) (PPV) thin films. The PPV films show non-uniform mesoscale dichroic domains with average domain size, approximately 0.3 mm, and the coefficient for linear dichroism is 1.25 x 10(4) cm(-1).