Phase Contrast Method in Spatial Filtering of Terahertz Beams

The presented research focuses on spatial filtering imaging methods, the use of the positive phase contrast (PPC) method, and optical diffractive elements with large apertures. The PPC method is characterized by a linear dependence of the introduced phase change at the object plane and the intensity distribution at the image plane. In this study, the PPC method was implemented in the 4f imaging setup, where the transparent (low-absorbing) object was imagined with the application of the phase filter placed in the Fourier plane. The evaluated objects and filters were manufactured using 3D printing fused deposition modelling (FDM) technology from exceedingly transparent cyclic olefin copolymer (COC) material. The experimental results demonstrate that the signal passing through the selected section of the evaluated object is enhanced even over 2.5 times if the proper filter size is selected.