Scanning near-field optical microscopy (SNOM, also known as NSOM) is a new local probe technique with a resolving power of 10--50 nm. Not being limited by diffraction, near-field optics (NFO) opens new perspectives for optical characterization and the understanding of optical phenomena, in particular in biology, microelectronics and materials science. SNOM, after first demonstrations in '83/'84, has undergone a rapid development in the past two to four years. The increased interest has been largely stimulated by the wealth of optical properties that can be investigated and the growing...