Showing papers by "Norman S. Kopeika published in 2010"

Generalized atmospheric turbulence: implications regarding imaging and communications

Abstract: At present, system design usually assumes the Kolmogorov model of refractive index fluctuation spectra in the atmosphere. However, experimental data indicates that in the atmospheric boundary layer and at higher altitudes the turbulence can be different from Kolmogorov's type. In optical communications, analytical models of mean irradiance and scintillation index have been developed for a traditional Kolmogorov spectrum and must be revised for non-Kolmogorov turbulence. The image quality (resolution, MTF, etc.) is essentially dependent on the properties of turbulent media. Turbulence MTF must be generalized to include non-Kolmogorov statistics. The change in fluctuation correlations of the refractive index can lead to a considerable change in both the MTF form and the resolution value. In this work, on the basis of experimental observations and modeling, generalized atmospheric turbulence statistics including both Kolmogorov and non-Kolmogorov path components are discussed, and their influence on imaging and communications through the atmosphere estimated for different scenarios of vertical and slant-path propagation. The atmospheric model of an arbitrary (non-Kolmogorov) spectrum is applied to estimate the statistical quantities associated with optical communication links (e.g., scintillation and fading statistics) and imaging systems. Implications can be significant for optical communication, imaging through the atmosphere, and remote sensing.

Optical imaging of hidden objects behind clothing

Abstract: Optical impulse-response characterization of diffusive media can be of importance in various applications, among them optical imaging in the security and medical fields. We present results of an experimental technique that we developed for acquiring the impulse response, based upon the Kramers–Kronig algorithm, and have been applied for optical imaging of objects hidden behind clothing. We demonstrate three-dimensional imaging with 5mm depth resolution between diffusive layers.

Low-cost plasma terahertz heterodyne image detection

Abstract: Miniature inexpensive neon indicator lamp plasma glow discharge detectors (GDD) are excellent candidates to serve as room temperature, low cost, terahertz (THz) radiation detectors and as pixels in THz imaging systems. Heterodyne amplification of low power signals via higher power reference beams is very important for THz imaging systems because it permits detection of much lower object beam intensities. An experimental result of 300GHz heterodyne detection by a single commercial GDD device costing about 30 cents is presented here. In heterodyne image detection a picture is taken of interference fringes or a hologram deriving from a coherent reference wave and a coherent wave reflected from or transmitted through an object. Transmission with in-line or zero angles between those two waves is important to widen the fringes. The GDD detector is transparent, so that it's possible to receive radiation from both sides, at 0 and 180 degree. This permit receiving the wave reflected from or transmitted through an object at 0 degree and the reference wave from the opposite direction at 180 degree. Such interference fringe widening can permit heterodyne direct imaging of the object instead of imaging the interference pattern.

Silicon photomultiplier and radiation detection: follow-up study and the path forward

Abstract: This work presents a comprehensive study of the Silicon Photomultiplier (SiPM) properties as a novel alternative for radiation detector light sensor. The SiPM low current consumption, its diminutive dimensions and the high gain make this technology of great interest for applications in portable radiation detection instrumentation based on scintillation material. The development progress in investigation of the performance of the device incorporation with CsI(Tl) scintillation crystal during the R&D timeline is presented. The research shows the improvement in two major parameters: the noise level and the resolution. The finding emphasizes that the utilization of the SiPM as the light converting device in radiation sensors is potentially applicable for radiation detection and isotope identification.

THz imaging using Glow Discharge Detector (GDD) focal plane arrays and large aperture quasi optic mirrors

Abstract: The properties of terahertz (THz) radiation are well known. They penetrate well most nonconducting media; there are no known biological hazards, and atmospheric attenuation and scattering is lower than for visual and IR radiation. Recently we have found that common miniature commercial neon glow discharge detector (GDD) lamps costing typically about 30 cents each exhibit high sensitivity to THz radiation, with microsecond order rise times, thus making them excellent candidates for such focal plane arrays. Based on this technology we designed, built and tested 4X4 and 8X8 GDD focal plane arrays. A line vector of 32 GDD pixels is being designed in order to increase the number of pixels in such arrays and thus the image resolution. Unique large aperture quasi optic mirrors were design and tested experimentally in this work. A new technology of light weight large aperture mirrors is proposed in this work. In this case a metal coating on plastic substrate is demonstrated. According to first experiments this technology proves to reliable with minimal deformation in LAB conditions. THz Images at 100 GHz were taken using this new inexpensive technology with good quality and resolution.