Fast and sensitive MMW imaging system with up-conversion readout working in the NIR zone

Abstract

Focal plane arrays (FPA) constructed using glow discharge detectors (GDD) as the pixel elements proved to be an inexpensive methodology for generating MMW (millimeter wave)/THz (terahertz) images. In the abnormal glow mode of operation, the weakly ionized plasma (WIP) in GDDs can be more responsive while interacting with the incident MMW/THz radiations. It has explicitly been found that the major influence of MMW/THz radiation on the emitted light spectrum from the GDD is located in the near-infrared (NIR) zone of the electromagnetic spectrum which is around 800 nm– 1000 nm. Also, there is no influence of the MMW/THz on the visual band ranging from 500 nm–600 nm emitted from the GDD. The up-conversion method utilized here refers to the detection of variations in the intensity of emitted light from the GDD due to the incident MMW radiation. A charge-coupled device (CCD) camera is employed here to generate MMW/THz images by capturing the light output from the GDD pixel elements on the FPA located in the image plane. The DC bias voltage emitted light from the GDD is much stronger than the modulated light produced as a result of the incident MMW/THz radiation. The major challenge of this work is to measure this minute variation in the GDD light output caused by the MMW/THz radiation and to distinguish it from the intense DC bias operation light of the GDD. For achieving this, we propose using an optical long-pass filter as a part of the CCD camera component, thus enhancing the performance of the suggested up-conversion method. The addition of the long-pass filter eliminates most of the highly intense visual spectrum from the light output of the GDD, thereby decreasing noise and making the up-conversion imaging more effective. Here, we demonstrated the feasibility of implementing GDD-based FPAs using up-conversion readout for MMW/THz imaging applications in the NIR regime by testing with a single GDD whose detection impact was captured using a CCD camera whose zoom lens was coupled with a long pass optical filter.