Dark-field imaging by active polymer slab waveguide

A dark-field imaging technique taking advantage of the active polymer slab waveguide (APSW) is experimentally investigated. The dye molecules (Rhodamine 6G, Rh6G) are doped in the polymer film for the launching of surface waves on the APSW, such as the surface plasmon polaritons on the Ag–polymer–air interface, evanescent fields at the polymer–air interface by the total internal reflection, or the guided modes. The localized surface waves will not radiate into the far-field space directly. When the specimens are placed on the surface of the APSW, these surface waves will be scattered to the far-field region, which forms the dark-field image of the specimen. Experimental results show that usage of APSW leads to high-contrast dark-field images with the conventional optical microscope system. The polymer film involved in the proposed dark-field microscopy brings about the merits of reduced roughness, good stability, bio-compatibility, and shorter wavelength of the illumination light source.