Chip-Based Near-Field Terahertz Microscopy

Near-field terahertz (THz) imaging is vital to investigations in subwavelength regions down to the micro/nanometer scale. This technology is particularly useful for examining objects, such as nanomaterials, polymers, cells, and biomolecules. The first part of this paper briefly explains two types of near-field THz imaging technologies: aperture type and apertureless type. The second part explains our chip-based near-field imaging technology. We perform collection-mode near-field THz imaging by scanning an evanescently coupled THz detector closely across a sample surface. The implementation of a magnetically tunable THz detection method further enables us to obtain frequency-selective near-field THz images. As an application of this technology, cryogenic THz-emission imaging is presented, wherein THz radiation associated with electron injection into a semiconductor device is imaged with no THz pump source. This technique provides direct information about the spatial distribution of electrons injected from an electrode into a semiconductor channel.