We proposed a simple and cost-effective method to manipulate the temporal and spectral properties of pulsed terahertz waves. A deep modulation of a pulse spectrum was both numerically and experimentally verified using Fresnel apertures with a radius ranging from several to several tens of the central wavelength of the broadband terahertz radiation. N-fold frequency minima were formed in the spectrum at a specific axial position behind the filter. Non-paraxial properties of this filter were also analyzed. A significant value (35%) of the ratio of the longitudinal to the transverse field component at the filter frequency was obtained. The measured results agree well with the simulation and theoretical predictions. The property of such a diffractive Fresnel notch filter can benefit the generation of longitudinal terahertz fields and relevant applications.

中文翻译：

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光谱菲涅耳滤波器，用于脉冲宽带太赫兹辐射

我们提出了一种简单且具有成本效益的方法来控制脉冲太赫兹波的时间和频谱特性。脉冲频谱的深度调制已使用菲涅耳孔径进行了数值和实验验证，其半径范围为宽带太赫兹辐射的中心波长的几倍至几十倍。在频谱中，在滤波器后面的特定轴向位置处形成了N倍的频率最小值。还对该滤光片的非傍轴特性进行了分析。获得了在滤波器频率下纵向场分量与横向场分量之比的显着值（35％）。测量结果与仿真和理论预测吻合良好。