High-resolution terahertz ptychography using divergent illumination and extrapolation algorithm

Abstract

By virtue of its versatile recording geometries, ptychography is a promising full-field lensless phase imaging approach in the prosperous research area of terahertz imaging. In this paper, we propose an extrapolation extended ptychographical iterative engine, named as the EE-PIE reconstruction algorithm, to increase the lateral resolution of terahertz ptychography. A divergent spherical beam is applied to illuminate the object, while diffraction patterns are recorded in the Fresnel region. The signal-to-noise ratio of the diffraction patterns is enhanced under divergent probe illumination, while the size of the diffraction patterns is numerically enlarged by the proposed algorithm. Both the reconstruction quality and the resolution are enhanced without adding to the complexity of the setup or increasing the data acquisition time. The proposed method is experimentally demonstrated using a cluster of phylloclades, a patterned polypropylene plate and a Siemens star target. Compared with the planar illumination, the resolution of the divergent spherical illumination is improved by 2.14 times. On this basis, the extrapolation algorithm further improves the experimental resolution by 1.26 times.