在300 - 1000 GHz的亚毫米波范围内的成像对于各种应用（包括安全检测，通过遮蔽成像和非破坏性评估）都是有用的。在这个频率范围内的波长范围从1mm到0.3mm，能穿透许多光学遮蔽物。形成穿透衣服的高分辨率图像的能力使得该频率范围内的成像对于距离距离的人员安全检查特别有效。

美国西北太平洋国家实验室（PNNL）以前已经开发出门控筛选系统，其操作在约30 GHz的毫米波频率范围的较低端。这些系统非常适合在门户内进行筛选，并可在小于1米的范围内实现约5mm的分辨率。

然而，增加这些系统的范围将显着降低由于其相对较长波长的衍射而导致的分辨率。在更高频率（例如350GHz）下的操作将能够在给定范围内提高分辨率的数量级，同时仍然实现足够的衣服渗透。 PNNL的门户成像系统依靠波前重建或全息成像技术来数学地集中图像。在亚毫米波中，由于系统对数据采集期间成像目标位置的微小变化的敏感性，这可能并不总是实用的。在这种情况下，使用透镜或反射镜的物理聚焦可能更实用。在本文中，我们研究了350 GHz附近成像安全筛选应用的有效性。使用全息波前重建技术呈现成像结果，以及基于聚焦反射器的成像系统。

Active Imaging at 350 GHz for Security Applications

Citation

Sheen DM, DL McMakin, JB Barber, TE Hall, and RH Severtsen.  2008.  "Active Imaging at 350 GHz for Security Applications."  In Proceedings of the SPIE: Passive Millimeter-Wave Imaging Technology XI , vol. 6948, p. 69480M.  International Society for Optical Engineering, Bellingham, WA.  doi:10.1117/12.778011

Abstract

Imaging in the sub-millimeter wave range of 300 – 1000 GHz is useful for a variety of applications including security screening, imaging through obscurations, and non-destructive evaluation. Waves in this frequency range have wavelengths ranging from 1 mm down to 0.3 mm and are able to penetrate many optical obscurants. The ability to form high-resolution images that penetrate clothing makes imaging in this frequency range particularly interesting for personnel security screening at standoff distances. The Pacific Northwest National Laboratory (PNNL) has previously developed portal screening systems that operate at the lower end of the millimeter-wave frequency range around 30 GHz. These systems are well suited for screening within portals and can achieve resolution of about 5 mm at ranges of less than 1 meter. However, increasing the range of these systems would dramatically reduce the resolution due to diffraction at their relatively long wavelength. Operation at much higher frequencies, for example 350 GHz, will enable an order of magnitude improvement of the resolution at a given range, while still achieving adequate clothing penetration. PNNL's portal imaging systems have relied on wavefront reconstruction, or holographic, imaging techniques to mathematically focus the imagery. In the sub-millimeter-wave, this may not always be practical due to sensitivity of the system to slight changes in the position of the imaging target during data collection. In this case, physical focusing using lenses or reflectors may be more practical. In this paper, we examine the effectiveness of imaging near 350 GHz for security screening applications. Imaging results are presented using the holographic wavefront reconstruction technique, as well as a focused reflector-based imaging system.