Detection of evanescent waves using disordered nanowires

Conventional optical microscopy is incapable of detecting evanescent waves scattered at a target object, which poses diffraction limit in the spatial resolution. This limitation can be overcome by placing a sub-wavelength structure near the object and converting evanescent waves into detectable propagating waves. In this study, we investigated the possibility of using disordered nanowires as special sub-wavelength structures for the detection of evanescent waves. To this end, we generated evanescent waves by using a half-sphere ball lens with high refractive index and measured the waves scattered by the nanowires deposited on the flat surface of the ball lens. We observed that a layer of randomly grown nanowires scattered the evanescent waves into the far-field region. We also found that the use of a shorter wavelength light source is advantageous in detecting the high spatial frequency component of the evanescent waves even with the shallower skin depth. Our study will pave the way for exploiting a disordered medium as a far-field superlens for the scanning-free near-field imaging.