Longitudinally polarized terahertz radiation offers access to the elementary excitations and particles that cannot be addressed by transverse waves. While transverse electric fields exceeding 1 MV/cm are widely utilized for nonlinear terahertz spectroscopy, longitudinally polarized terahertz waves at this field strength are yet to be realized. In this paper, we experimentally demonstrate that by focusing radially polarized terahertz fields generated from laser–thin metallic foil interaction, longitudinally polarized terahertz with record-breaking field strength above 1.5 MV/cm can be obtained. Furthermore, we also traced the evolution of the geometric phase of the longitudinal component as it propagates through focus. A novel scheme based on noncollinear electro-optic detection has been utilized to unambiguously measure the polarization states. Our result will scale up the nonlinear spectroscopy of solid materials and particle acceleration experiments where on-axis polarization plays a crucial role.

中文翻译：

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激光-薄箔相互作用产生的多MV / cm纵向极化太赫兹脉冲

纵向极化的太赫兹辐射提供了基本激发和无法通过横波解决的粒子的通道。尽管超过1 MV / cm的横向电场被广泛用于非线性太赫兹光谱学，但是在这种场强下，仍需要实现纵向极化的太赫兹波。在本文中，我们通过实验证明，通过聚焦由激光-薄金属箔相互作用产生的径向极化太赫兹场，可以获得具有破纪录的场强超过1.5 MV / cm的纵向极化太赫兹。此外，我们还追踪了纵向分量通过焦点传播时几何相位的演变。一种基于非共线电光检测的新颖方案已被用来明确测量偏振态。