To improve the accuracy of material identification in millimeter- and terahertz-wave nondestructive imaging during security and other inspections, it is important to perform both amplitude and phase imaging. Highly coherent sources generated based on the frequency multiplication of stable microwave sources are promising for these applications. However, this method reduces the fidelity of the image due to the interference phenomenon with reflected waves on the sample surface. In this paper, we propose and demonstrate amplitude and phase imaging using an incoherent free-running self-oscillating device. We used a Gunn oscillator operating at 122.5 GHz as a millimeter-wave source and a photoconductive antenna as a detector. The frequency and phase noise of the source are canceled by the low-frequency electronics, which realize phase imaging using an incoherent source. We performed amplitude and phase imaging on low-loss polypropylene objects and obtained ∼22 times higher imaging contrast in the latter than in the former. Furthermore, we were able to obtain high-fidelity imaging results with less interference in both amplitude and phase imaging. The proposed system is reliable and inexpensive because the source operates with a DC power source only, and the frequency and phase noise-cancellation electronics consist of low-frequency circuits. Moreover, because the noise-cancellation electronics are independent of the RF frequency, the system is easily extendible to the higher frequency region to improve its spatial resolution. This paves the way for the realization of a diode-based, sensitive, and low-cost integrated system that allows both amplitude and phase imaging for material identification in security inspections.

中文翻译：

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使用非相干自由运行自振荡设备在毫米和太赫兹波段中进行振幅和相位成像

为了提高安全性和其他检查过程中毫米波和太赫兹波无损成像中材料识别的准确性，执行振幅成像和相位成像都是很重要的。基于稳定微波源的倍频而产生的高度相干源有望用于这些应用。但是，由于样品表面反射波的干扰现象，该方法降低了图像的保真度。在本文中，我们提出并演示了使用非相干自由运行自振荡设备的振幅和相位成像。我们使用工作在122.5 GHz的Gunn振荡器作为毫米波源，使用光电导天线作为检测器。源的频率和相位噪声被低频电子设备消除，使用非相干光源实现相位成像 我们对低损耗聚丙烯物体进行了幅度和相位成像，后者的成像对比度比前者高约22倍。此外，我们能够在振幅和相位成像方面获得较少干扰的高保真成像结果。所提出的系统是可靠且廉价的，因为该源仅使用直流电源工作，并且消除频率和相位噪声的电子设备由低频电路组成。此外，由于消除噪声的电子设备与RF频率无关，因此该系统可轻松扩展到更高的频率区域，以提高其空间分辨率。这为实现基于二极管的，灵敏的，