Probing the Optical Near-Field

Since the description of diffraction from the seventeenth century and the development of optical microscopy that has followed, many approaches have been developed for breaking the diffraction limit. Following the first proposition of near-field optical microscopy made in the 1920s, the first experimental demonstrations started in the early 1980s through scanning near-field optical microcopy, within the context of the swift development of scanning probe microscopies. Since, different alternative approaches and concepts have emerged for probing the optical near-field with a sub-wavelength resolution. The chapter is divided into four main sections. In Sect. 4.2, important theoretical principles will be reminded. They will allow the reader to acquire a general background in near-field optics. Section 4.3 describes how it is possible to probe the near-field with physical optical nano-antenna. In particular, different approaches of scanning near-field optical microscopy will be discussed. Section 4.4 is dedicated to the way free electrons can be used for probing the near-field. Section 4.5 deals with the use of nanoscale photochemistry for probing the optical near-field. These three approaches present respective features and assets that will be illustrated by examples of achievements from the literature.