Terahertz near-field spectroscopy for various applications

Terahertz (THz = 1012 Hz) spectroscopy has been recognized as a promising analytical technique for non-destructive, highly accurate investigation. However, despite its advantages, relatively long-wavelength and weak light-matter interaction limit the potential of these techniques to measure physical phenomena occurring within small areas and molecules, where lots of physical properties have been discovered. In this review, we introduce recent advances in THz near-field techniques as contact-free and non-invasive methods, particularly scattering-type scanning near-field optical microscopy (s-SNOM) with atomic force microscope (AFM) tip and transmission-type of photoconductive antenna microprobe (PCAM)-based THz near-field microscopy. Furthermore, practical applications of these cutting-edge spectroscopic methods are discussed.