Design optimization of terahertz near-field detectors

Spatial resolution of the near-field imaging technique with Terahertz pulses is mainly limited by strong signal attenuation in the aperture of the probe. We demonstrate that probe sensitivity can be significantly improved by placing a detecting element into the near-field zone of the probe aperture. In this case the evanescent modes of the field transmitted through the aperture contribute to the detected signal. Electric field is experimentally measured in the near-field zone of a subwavelength aperture. Numerical calculations based on a simple two-dimensional model are used to analyze effects of the probe geometry.