Direct measurement of a radially polarized focused evanescent field facilitated by a single LCD

We demonstrate theoretically and experimentally an anomaly in the intensity distribution at the focal region of a Laguerre-Gaussian beam, when such a beam is focused by a high numerical aperture objective lens through an index-mismatched interface satisfying the total internal reflection condition. An asymmetric rotation of the focal field arising from the interplay of the phase shift induced by the total internal reflection and the helical phase of the Laguerre-Gaussian beam has been experimentally observed by a scanning near-field optical microscope. A cross-section analysis shows that the experimental results match well with the theoretical predictions.