Kulya Maksim, Semenova Varvara, Gorodetsky Andrei, Bespalov Victor G, Petrov Nikolay V
Appl Opt. 2019 Feb 10;58(5):A90-A100. doi: 10.1364/AO.58.000A90.
A comprehensive characterization of the diffraction properties of terahertz (THz) pulsed broadband vortex beams consisting of several electromagnetic field oscillations requires state-of-the-art techniques for studying the evolution of a wavefront as it propagates. For this purpose, we have applied the capabilities offered by THz pulse time domain holography. Accurate metrological study of pulsed single-period THz field propagation allowed us to reveal the spatio-temporal and spatiospectral couplings in broadband uniformly topologically charged vortex beams. Here, we reveal dynamics of such beam propagation in a free space as well as in the experiment with edge diffraction with 50% blocking of the beam focal waist. In this study, we compare the dynamics of freely propagating and edge-diffracted THz vortex. Despite the fact that in the amplitude representation one can observe the emergence of strong asymmetry, analysis of the spectral trajectory of the singular point at some distance from the obstacle and the visualization of phase distribution for individual spectral components testify to the conservation of transverse energy circulation. Similar to the edge diffraction of monochromatic optical vortices, it can be interpreted as self-reconstruction of vortex properties. The given term has not previously been used for the case of pulsed broadband THz beams, to the best of our knowledge.
对由多个电磁场振荡组成的太赫兹（THz）脉冲宽带涡旋光束的衍射特性进行全面表征，需要先进的技术来研究波前在传播过程中的演变。为此，我们应用了太赫兹脉冲时域全息术所提供的功能。对脉冲单周期太赫兹场传播进行精确的计量学研究，使我们能够揭示宽带均匀拓扑电荷涡旋光束中的时空和空间光谱耦合。在此，我们揭示了这种光束在自由空间以及在光束焦腰50%被阻挡的边缘衍射实验中的传播动力学。在本研究中，我们比较了自由传播和边缘衍射的太赫兹涡旋的动力学。尽管在幅度表示中可以观察到强烈不对称性的出现，但对距障碍物一定距离处奇异点的光谱轨迹分析以及对各个光谱分量的相位分布可视化表明横向能量环流得以保留。与单色光学涡旋的边缘衍射类似，这可以解释为涡旋特性的自我重建。据我们所知，此前该术语尚未用于脉冲宽带太赫兹光束的情况。
