Measurements and simulations of the optical parameters of the Glow Discharge Detector (GDD) Focal Plane Array (FPA) millimeter wavelength imaging system Moshe Shilemay 1 , Daniel Rozban 1,2 , Assaf Levanon 2 , Yitzhak Yitzhaky 2 , Natan S. Kopeika 2 , Amir Abramovich 1 1 Department of Electrical and Electronic Engineering, Ariel University Center of Samaria, Ariel, Israel 2 Department of Electro-Optical Engineering, Ben Gurion University of the Negev, Beer-Sheva, Israel Abstract — The optical parameters of millimeter wavelength (MMW) imaging system are under investigation in this study. The Optical Transfer Function (OTF) was measured and simulated in this study. The performance and quality of the MMW imaging system were tested using point source objects and Point Spread Function (PSF) was obtained. The MMW imaging system is composed of large aperture 500 mm spherical mirror, CW MMW source and 8X8 Glow Discharge Detector (GDD) Focal Plane Array (FPA). In order to investigate the above optical parameters a diagonal mirror was used in order to allow vertically placing of objects rather than horizontally. In order to avoid stray light, absorber materials were placed around the quasi-optic set-up. Special metal resolution charts and point source objects were manufactured and imaged. The influence of the diffraction has been taken care in the calculations and simulations. The experimental results showed very good agreement with the simulations and calculations results. Index Terms— Glow Discharge Detector, millimeter wavelength, Plasmas, Terahertz imaging. I. INTRODUCTION maging systems in the electromagnetic spectrum between 100 GHz and 10 THz are required for applications in medicine, communications, homeland security, and space technology. This is because terahertz (THz) radiation and MMW penetrates dielectric materials well, there is no known ionization hazard for biological tissue, and atmospheric attenuation of THz and MMW radiation is lower compared to infrared and optical rays. The lack of inexpensive room temperature detectors and FPAs in this spectral region makes it difficult to develop detection and imaging systems, especially real-time ones. The GDD is a very inexpensive room temperature detector which is used in this study for direct THz radiation detection and imaging. There are several other room temperature THz detectors that are used for direct detection. The most popular detectors are Golay cells, pyroelectric and microbolometers, many of which are too slow for video frame rates and are very expensive. All are described in detail in [1]. In addition, there are THz cooled detectors which are also very expensive [1]. The advantages of GDD are: low cost, high responsivity, broad band, room temperature operation, and fast response. A candidate for THz FPA pixels is miniature neon indicator lamps N523 of international light technology (Peabody, MA) which was tested experimentally and found to be a very good THz detector [2]. Its NEP is on the order of 10 -9 W/Hz 1/2 , and rise time is on the order of a microsecond and less. The detection mechanism of the GDD involves both enhanced cascade ionization [3-8] which was found to be dominant and enhanced diffusion current [3, 4, 7, 9-11] caused by the incident terahertz wave. The former increases lamp current, while the latter decreases it. The quality of an imaging system can be defined by its Point Spread Function (PSF) or its corresponding Optical Transfer Function (OTF). The PSF describes the imaging system response to a point source in two dimensions, and is analogous to the impulse response. The OTF is defined as the two dimensional Fourier transform of the PSF normalized to its own maximum value. The OTF is a complex value, composed of the Modulation Transfer Function (MTF) and the Phase Transfer Function (PTF), which are the magnitude and the phase of the OTF, respectively. () = ∬ ( , , , )exp(− − ) , , ∬ ( , , , ) , , = , (,) = (1) Here Sω ,ω is the Fourier transform of the point spread function s(x, y). In imaging system's quality evaluation it is the MTF that is most relevant, since it carries information about the size and contrast limitations, rather than position and orientation information that is included in the phase component, which can have a secondary effect. The MTF is a parameter that I