4. Near-field optical microscope

4.1 Principles of the near-field optical microscope

The limit of spatial resolution reached in conventional optical microscopy (the so-called Abbe diffraction limit) is of the order of λ/2 where λ is the wavelength of the radiation. Electromagnetic waves at wavelength λ that interact with an object are diffracted into two components: progressive waves at low spatial frequency (< 2/λ) and evanescent waves at spatial frequency greater than 2/λ. Diffraction acts as a low-pass filter with respect to the sample's spatial frequencies, and only the progressive waves reach the detector placed far from the sample,...