The appearance of the spurious absorption frequencies caused by the frequency conversion process at the broadband THz pulse propagation in a medium is theoretically and experimentally discussed. The spurious absorption frequencies appear due to both the frequency doubling and generation of waves with sum or difference frequency. Such generation might occur because of the nonlinear response of a medium or its non-instantaneous response. This phenomenon is confirmed by the results of a few physical experiments provided with the THz CW signals and broadband THz pulses that are transmitted through the ordinary or dangerous substances. A high correlation between the time-dependent spectral intensities for the basic frequency and generated frequencies is demonstrated while using the computer simulation results. This feature of the frequency conversion might be used for the detection and identification of a substance.

中文翻译：

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脉冲THz TDS问题中由于频率转换过程导致的杂散吸收频率出现。

从理论上和实验上讨论了在宽带THz脉冲在介质中传播时由频率转换过程引起的寄生吸收频率的出现。杂散吸收频率的出现是由于倍频和具有总和或不同频率的波的产生。由于介质的非线性响应或其非瞬时响应，可能会发生这种生成。通过通过普通或危险物质传输的太赫兹连续波信号和宽带太赫兹脉冲提供的一些物理实验结果证实了这一现象。使用计算机仿真结果时，证明了基本频率的时间相关频谱强度与生成的频率之间的高度相关性。