Resolution Limits of Hyper-Hemispherical Silicon Lens-Integrated THz Cameras Employing Geometrical Multiframe Super-Resolution Imaging

In this article, we present a comprehensive study to understand the image formation and associated resolution limitations of hyper-hemispherical high-resistivity floating-zone silicon (HRFZ-Si) lens-integrated terahertz (THz) cameras, and we extend this understanding into THz super-resolution imaging applications. Along these lines, design tradeoffs between fixed field-of-view and frequency-dependent angular resolution of such cameras are also discussed. The present study is based on investigations of a CMOS THz camera that is made of a 32 ×32-pixel focal plane array sensor and a 15-mm diameter objective hyper-hemispherical HRFZ-Si lens. Two experiments are performed at 0.652 THz. In the first experiment, THz geometrical multiframe super-resolution imaging is performed to demonstrate that such cameras can always reach the maximum achievable resolution in their entire operating bandwidth. In the other, a full radiation pattern scan is performed to measure aberrations of off-axis displaced pixels in order to give a comprehensive picture of the camera's resolution behavior across the full camera frame. The investigations and discussions are general in nature and should be applicable to any broadband THz camera.

I. Introduction

Many common materials such as fabric, cardboard, paper, wood, masonry, plastic, and ceramics are opaque to the visible or infrared radiation but transparent to terahertz (THz) radiation [1]. THz radiation manifests a strong attenuation in water and strong reflection from metals. These particular properties of THz radiation make it suitable for a growing number of potential applications, including biomedical imaging, security and defense, industrial quality assurance systems, and technical diagnostic systems [2].