High-frequency near-field microscopy

Conventional optics in the radio frequency (rf) through far-infrared (FIR) regime cannot resolve microscopic features since resolution in the far field is limited by wavelength. With the advent of near-field microscopy, rf and FIR microscopy have gained more attention because of their many applications including material characterization and integrated circuit testing. We provide a brief historical review of how near-field microscopy has developed, including a review of visible and infrared near-field microscopy in the context of our main theme, the principles and applications of near-field microscopy using millimeter to micrometer electromagnetic waves. We discuss and compare aspects of the remarkably wide range of different near-field techniques, which range from scattering type to aperture to waveguide structures.