Passive Terahertz Microscopy with a Highly Sensitive Detector

A passive terahertz (THz) microscope has been developed for sensitive imaging of spontaneous THz radiation. The THz microscope consisted mainly of a Ge objective lens, a confocal pinhole, Ge relay lenses, and a highly sensitive THz detector (Charge-Sensitive Infrared Phototransistor, CSIP). Then experimental examinations of the developed microscope were performed. First, THz signals, which were related to the spontaneous thermal radiation, were reasonably obtained. Next a passive THz image was successfully achieved. The lateral resolution of the microscope was derived to be 25 m, where the depth resolution was derived to be 30 m. In addition, the lateral resolution was not degraded despite the coverage of GaAs and Si. These results indicate that the THz microscope enables passive imaging with high resolution. This study opens the door to novel THz measurement technology, which can reveal physical and biological phenomena such as molecular motions, biomolecular protein interactions, and semiconductor conditions in their true colors.