We have studied the applicability of high- T_c Josephson junctions (JJs) and Hilbert-transform spectral analysis (HTSA) for characterization of pulsed terahertz (THz) radiation. We have reconsidered the extension of HTSA into the THz range, including an impact of such emerging factors as nonequilibrium voltage fluctuations and dc Joule heating in high- T_c JJs, and found an unexpected weak temperature dependence of Josephson linewidth δf and a spectral dependence δf(f) with a minimum. Due to this analysis, we have chosen YBa ₂ Cu ₃ O _7-x bicrystal JJs for experimental study. The JJs have analyzed pulsed THz radiation from quantum cascade lasers (QCLs) located in the same cryogenic environment at 50 K. The spectra recovered by the JJ with R_n = 43 Ω consist of a line with a central frequency around 2.2 THz, which have a symmetrical form and the linewidth of 90 GHz close to the intrinsic Josephson linewidth of this JJ. The spectra measured by the JJ with R_n = 7 Ω and the intrinsic Josephson linewidth of 16 GHz consist of several lines at the frequencies f_i around 2.2 THz, which are due to the excitation of different resonant modes in the active volume of the QCL. The difference between the fitted central frequencies f ₂ - f ₁ of the strong lines and the ratio of their intensities are in agreement with the spectrum of the same QCL measured by Fourier spectroscopy. The developed technique paves the way for detailed and rapid characterization of pulsed THz sources in the frequency domain.

中文翻译：

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原位 量子级联激光器的太赫兹脉冲辐射的希尔伯特变换光谱分析。Ť _ç 约瑟夫森交界处

我们已经研究了高 Ť _ç约瑟夫森结（JJs）和希尔伯特变换光谱分析（HTSA）用于表征脉冲太赫兹（THz）辐射。我们已经重新考虑将HTSA扩展到THz范围，包括新兴因素的影响，例如非平衡电压波动和高 Ť _ç JJs，并发现了约瑟夫森线宽的意想不到的温度依赖性 δf 和光谱依赖性 δf（f）最少。由于这种分析，我们选择了YBa ₂ Cu ₃ O _7-x双晶JJ进行实验研究。JJ分析了位于相同低温环境下的50 K量子级联激光器（QCL）的脉冲THz辐射。[R _ñ= 43Ω由中心频率约为2.2 THz的一条线组成，该线具有对称形式，并且90 GHz的线宽接近此JJ的固有约瑟夫森线宽。JJ用[R _ñ = 7Ω，固有的约瑟夫森线宽为16 GHz，在频率上由几条线组成 ˚F_我大约2.2 THz，这是由于QCL的有效体积中不同共振模式的激发所致。拟合中心频率之间的差异F ₂ -F ₁条强线及其强度比与通过傅里叶光谱法测量的同一QCL的光谱一致。所开发的技术为在频域中对脉冲太赫兹源进行详细，快速的表征铺平了道路。