Aperture-Type Terahertz Near-Field Imaging With A Cylindrical Frustum-Shaped Plastic Probe

We designed an aluminum-coated plastic probe made from the combination of cylinder and a frustum of a cone for terahertz near-field imaging. The bunching width of the probe is 12 mu m and the electric field intensity enhancement factor just outside the probe tip reaches up to 25. An imaging resolution obtained through near-field imaging experiments on a variety of targets, including narrow metals and narrow media, is 6 mu m (lambda/450) at 0.11 THz. By adopting an adaptive threshold segmentation image processing algorithm that combines Hilbert scanning and wavelet transform, the influence of a large area of metal near the imaging area on the imaging result is successfully suppressed. Imaging of a scratch on the plastic substrate makes the new probe feasible for quality identification of nonmetallic cultural relics. (C) 2021 Optical Society of America