  Drude model successfully quantifies the optical constants for bulk matter,
but it is not suitable for subwavelength objects. In this paper, terahertz
near-field optical microscopy and finite element simulation are used to study
gold patches fabricated by Gallium etching. Electron transport is discovered in
determining the optical signal strength. The signal from substrate is more
complicated and still not fully understood. As the etching area decreases,
near-field interaction is not dominated by doping concentration, and a higher
signal is observed near connected metals. With the help of simulation, the
abnormal enhancement phenomenon is discussed in detail, which lays the
foundation for further experimental verification.
