Spatial filtering based terahertz imaging of low absorbing objects

Abstract Terahertz (THz) imaging can serve as a versatile instrument to disclose contents of various packages or discriminate its constituents. Particular attention deserves a case when packaged objects display low absorption in THz frequencies inducing thus immense obstacles in direct image recording due to a poor signal-to-noise ratio and small contrast. To tackle these problems and extend an assortment of application two spatial filtering methods – phase contrast and dark field – were demonstrated both experimentally and theoretically to resolve weakly absorbing objects in THz imaging at 0.3 THz. The approach was implemented via employment of two different THz imaging setups – using focused and collimated beams – and detecting signals by sensitive antenna-coupled titanium-based microbolometers. The proposed approaches taking advantage of phase contrast and dark field methods exhibit enhancement in images contrast up to 10 dB and 30 dB, respectively, and an order of magnitude increased signal-to-noise ratio, opening thus promising route for functional applications. It is believed that it will impact wider THz implementation in medicine and biology-related issues, where weak absorbance of THz radiation in many cases is inherent feature of objects under test.