Abstract
Throughout the 20th century, it was widely accepted that a light microscope relying on conventional optical lenses cannot discern details that are much finer than about half the wavelength of light (200-400 nm), due to diffraction.
However, in the 1990s, the viability to overcome the diffraction barrier was realised and microscopy concepts defined, that can resolve fluorescent features down to molecular dimensions.
In this lecture, I will discuss the simple yet powerful principles that allow neutralising the limiting role of diffraction. In a nutshell, feature molecules residing closer than the diffraction barrier are transferred to different (quantum) states, usually a bright fluorescent state and a dark state, so that they become discernible for a brief period of detection.
