Surface wave illumination Fourier ptychographic microscopy.

Abstract

We propose a novel microscopy method, combining surface wave illumination and the Fourier ptychographic microscopy (FPM) algorithm to achieve super-resolution (SR) imaging. In our system, an oil-immersion objective lens is used to excite both the total internal reflection (TIR) evanescent waves and the surface plasmon waves (SPWs), which illuminate the sample with large wave vectors. Through the FPM algorithm, a resolution approximately twice that of conventional wide-field microscopy is obtained. Meanwhile, we could retrieve the sample's quantitative phase map in order to obtain its surface profile. Importantly, the field enhancement from a SPW has improved the contrast of the reconstructed images, which is critical for revealing the finer structural details of the specimen. In our experiments, we have imaged metallic gratings with a 120 or 150 nm wide line and trench features. We accurately retrieved their axial dimensions with a lateral resolution better than 240 nm that is close to the theoretical resolution of 215 nm, thus demonstrating the quantitative phase imaging capability of our technique. As this approach provides a label-free solution for intensity and phase imaging of samples with lateral resolution exceeding the limit introduced by the optical system, it can be potentially used in a wide range of noninvasive biological imaging applications.