Precise real-time polarization measurement of terahertz electromagnetic waves by a spinning electro-optic sensor
Precise real-time polarization measurement of terahertz electromagnetic waves by a spinning electro-optic sensor
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DOI：
10.1063/1.3683570
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发表时间：
2012-02-01
影响因子：
1.6
通讯作者：
Watanabe, Shinichi
中科院分区：
文献类型：
--
作者：
Yasumatsu, Naoya;Watanabe, Shinichi
提出并发展了一种快速、精确地确定飞秒激光脉冲产生的相干太赫兹电磁波偏振方向的方法。测量系统由传统的太赫兹时域光谱系统与电光（EO）采样方法，但我们添加了一个新的功能，在EO晶体是连续旋转的角频率ω。我们发现了一个简单而有用的配方EO信号作为晶体取向的函数，这使得锁定的检测电场振幅和绝对偏振方向的太赫兹波相对于探测激光脉冲偏振方向在同一时间。单次测量完成约两个周期的晶体旋转（类似于21 ms），我们实验证明，偏振测量的准确性不会受到长期的太赫兹脉冲的振幅波动。通过重复测量测得的偏振方向分布与标准偏差为sigma = 0.56度的高斯分布函数非常拟合。该技术可用于太赫兹电磁波偏振态的快速直接测定，用于偏振成像以及精确的太赫兹法拉第或克尔旋转光谱。(C)2012年美国物理学会。[http：//dx.doi.org/10.1063/1.3683570]
We propose and develop a method to quickly and precisely determine the polarization direction of coherent terahertz electromagnetic waves generated by femtosecond laser pulses. The measurement system consists of a conventional terahertz time-domain spectroscopy system with the electro-optic (EO) sampling method, but we add a new functionality in the EO crystal which is continuously rotating with the angular frequency omega. We find a simple yet useful formulation of the EO signal as a function of the crystal orientation, which enables a lock-in-like detection of both the electric-field amplitude and the absolute polarization direction of the terahertz waves with respect to the probe laser pulse polarization direction at the same time. The single measurement finishes around two periods of the crystal rotations (similar to 21 ms), and we experimentally prove that the accuracy of the polarization measurement does not suffer from the long-term amplitude fluctuation of the terahertz pulses. Distribution of the measured polarization directions by repeating the measurements is excellently fitted by a Gaussian distribution function with a standard deviation of sigma = 0.56 degrees. The developed technique is useful for the fast direct determination of the polarization state of the terahertz electromagnetic waves for polarization imaging applications as well as the precise terahertz Faraday or Kerr rotation spectroscopy. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3683570]