The high sensitivity detection of terahertz radiation is crucial for many chemical sensing, biomedical imaging, security screening, nondestructive quality control, high-data-rate communication, atmospheric, and astrophysics sensing applications. Among various terahertz detection techniques, heterodyne detection is of great interest for applications that require high spectral resolution. Heterodyne detection involves mixing the received terahertz radiation with a reference terahertz signal provided by a local oscillator and then down-converting it to an intermediate frequency for detection. The frequency of the intermediate frequency signal is usually chosen to be in the radio frequency regime, so that it can be accurately analyzed by well-developed radio frequency electronics, including amplifiers, filters, and spectrometers, for further processing. Heterodyne terahertz detection offers two major advantages over direct terahertz detection. First, the detected terahertz radiation is effectively enhanced by the reference local oscillator signal through the mixing process, thereby enabling the detection of very weak terahertz signals. Second, the detected noise power is effectively reduced by limiting the detected spectral bandwidth to the bandwidth of the intermediate frequency electronics. In this article, we present a broad overview of various types of heterodyne terahertz receivers, which utilize different electronic and optoelectronic techniques to down-convert the received terahertz signal to a radio frequency signal. We describe how the inherent nonlinearity of a Schottky diode, superconductor-insulator-superconductor junction, hot electron bolometer, and field-effect transistor can be utilized to mix the received terahertz radiation with a reference local oscillator signal from a gas laser, quantum cascade laser, photomixer, Gunn diode, IMPATT diode, and frequency multiplier and then down-convert it to a radio frequency signal. The down-converted radio frequency signal can be subsequently detected and analyzed by various backend spectrometers, including filter bank, acousto-optical, autocorrelator, fast Fourier transform, and chirp transform spectrometers. We also discuss how a photomixer pumped by a heterodyning optical beam can be used to down-convert the received terahertz radiation to a radio frequency signal with far fewer bandwidth constraints than conventional techniques. The advantages and disadvantages of different heterodyne receivers in terms of their noise performance, operation frequency, operation bandwidth, and operation temperature are discussed in detail.

中文翻译：

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通过电子和光电混频器进行外差太赫兹检测

太赫兹辐射的高灵敏度检测对于许多化学传感、生物医学成像、安全筛查、无损质量控制、高数据速率通信、大气和天体物理学传感应用至关重要。在各种太赫兹检测技术中，外差检测对于需要高光谱分辨率的应用非常重要。外差检测涉及将接收到的太赫兹辐射与本地振荡器提供的参考太赫兹信号混合，然后将其下变频到中频进行检测。中频信号的频率通常选择在射频范围内，以便可以通过发达的射频电子设备（包括放大器、滤波器和光谱仪）对其进行准确分析，作进一步处理。与直接太赫兹检测相比，外差太赫兹检测具有两大优势。首先，检测到的太赫兹辐射通过混频过程被参考本地振荡器信号有效增强，从而能够检测到非常微弱的太赫兹信号。其次，通过将检测到的频谱带宽限制为中频电子设备的带宽，有效地降低了检测到的噪声功率。在本文中，我们广泛概述了各种类型的外差太赫兹接收器，它们利用不同的电子和光电技术将接收到的太赫兹信号下变频为射频信号。我们描述了肖特基二极管、超导体-绝缘体-超导体结、热电子辐射热计、场效应晶体管可用于将接收到的太赫兹辐射与来自气体激光器、量子级联激光器、光混合器、耿氏二极管、IMPATT 二极管和倍频器的参考本地振荡器信号混合，然后将其下变频为射频信号。下变频后的射频信号可以随后被各种后端光谱仪检测和分析，包括滤波器组、声光、自相关器、快速傅立叶变换和线性调频变换光谱仪。我们还讨论了如何使用由外差光束泵浦的光混合器将接收到的太赫兹辐射下变频为射频信号，其带宽限制比传统技术少得多。不同外差接收机在噪声性能方面的优缺点，