2. Evanescent waves, rulers of the nanoworld

2.1 What is an evanescent wave?

As we saw earlier, Rayleigh's criterion establishes a physical barrier that renders details smaller than half the illumination wavelength unobservable. In the course of its propagation, light loses the information it contains concerning these small details, just as if the medium in which light propagates were a filter for sub-wavelength details, and therefore a low-pass filter for spatial frequencies (figure 2 ). When we illuminate an object with no fine detail and observe the...