THz detector and real-time imaging system developments at INO

In 2005, INO began research and development of terahertz (THz) imaging systems with the optimization of a microbolometer focal plane array (FPA) for frequencies from 5 THz to 95 GHz. Initial FPAs were fabricated in 2007 and since then, much progress has been made. The latest FPA design consists of 384 x 288 pixels having dimensions of 13.44 x 10.08 mm with 35 microns pixel size. The pixel design and fabrication, the wideband absorber deposition and the detector vacuum packaging are all performed in-house. In 2008, a low-noise electronic camera core was designed around the detector to complete the THz camera core, as was a custom F/0.95, 44 mm objective lens. The complete camera was paired with a Quantum Cascade Laser, and the first video-rate images were taken in 2009.

While the first videos taken with the camera proved the real-time capabilities of the INO imager, improvements were needed in the quality of the imagery for detection and identification purposes. To overcome this challenge, fast, high-quality optics were designed. Furthermore, commercially available terahertz sources are coherent, and thus are not ideal for imaging since given their irregular beam shape and non-uniformity. Over the years, INO has designed and fabricated numerous optical components to condition the beam and reduce its spatial coherence thus significantly improving the quality of the THz images.

This paper presents an overview of the status of terahertz imaging at INO. A review of the achievements and progress made will be presented along with example images. Next, the difficulties and limitations in the THz regime will also be discussed. The presentation will conclude with our planned future steps forward.