超宽带对数螺旋天线太赫兹光谱中的群延迟
Group delay in THz spectroscopy with ultra-wideband log-spiral antennae
摘要：
我们报告的群延迟观察连续波太赫兹光谱的基础上光混频相敏零差检测。我们讨论了实验装置对发射臂和接收臂之间的相位差Δ τ（ν）的不同贡献。基于三种贡献的简单模型产生了Δ τ（ν）的整体行为的定量描述。首先，光程长度差产生频率线性项。其次，超宽带对数螺旋天线在频率相关的有源区中有效地辐射和接收，在最简单的模型中，有源区是周长等于波长的环形区域。相应的项在100 GHz和1 THz之间变化大约6 π。第三个贡献源于光混合器阻抗。相反，导数（dΔ ε/ dν）由驻波引起的Δ ε（ν）的周期性调制的贡献主导，例如，在光溷合器的硅透镜中。此外，我们还讨论了傅里叶变换后的频谱，它与时域实验中的波形是等价的。在时域中，对数螺旋天线引入的群延迟引起强啁啾信号，其中低频被延迟。校正天线和光混合器的贡献会产生尖锐的峰值或“脉冲”，从而有助于对我们的连续波数据进行时域分析。
英文摘要：
We report on the group delay observed in continuous-wave terahertz spectroscopy based on photomixing with phase-sensitive homodyne detection. We discuss the different contributions of the experimental setup to the phase difference Δϕ(ν) between transmitter arm and receiver arm. A simple model based on three contributions yields a quantitative description of the overall behavior of Δϕ(ν). Firstly, the optical path-length difference gives rise to a term linear in frequency. Secondly, the ultra-wideband log-spiral antennae effectively radiate and receive in a frequency-dependent active region, which in the most simple model is an annular area with a circumference equal to the wavelength. The corresponding term changes by roughly 6 pi between 100 GHz and 1 THz. The third contribution stems from the photomixer impedance. In contrast, the derivative (dΔϕ/ dν) is dominated by the contribution of periodic modulations of Δϕ(ν) caused by standing waves, e.g., in the photomixers' Si lenses. Furthermore, we discuss the Fourier-transformed spectra, which are equivalent to the waveform in a time-domain experiment. In the time domain, the group delay introduced by the log-spiral antennae gives rise to strongly chirped signals, in which low frequencies are delayed. Correcting for the contributions of antennae and photomixers yields sharp peaks or "pulses" and thus facilitates a time-domain-like analysis of our continuous-wave data.
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