The efficient circular-polarized terahertz (THz) emission is important for THz imaging technology and basic scientific research. In order for it, we have made a simple and all-passive design to achieve collinear and co-rotating circular-polarized two-color laser fields. The collinearity allows us to manipulate accurately the relative phase between two-color lasers. For a given relative phase, our experiments show the efficient quasi-circular-polarized THz emission can be generated from an air-plasma pumped by the two-color fields. The emitted THz power is ~2.5 times of which pumped by linear-polarized two-color laser fields. Our results also indicate that quasi-circular-polarization is stable against different pump power and plasma-distance.

中文翻译：

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共线和圆偏振双色激光场泵浦的空气等离子体有效生成近圆偏振太赫兹

高效的圆极化太赫兹（THz）发射对于太赫兹成像技术和基础科学研究至关重要。为此，我们进行了一个简单而又无源的设计，以实现共线和同向旋转的圆偏振两色激光场。共线性使我们能够精确地操纵双色激光器之间的相对相位。对于给定的相对相位，我们的实验表明，可以通过由两色场泵浦的空气等离子体产生有效的准圆极化THz发射。发射的太赫兹功率约为线性偏振双色激光场泵浦的2.5倍。我们的结果还表明，准圆极化对于不同的泵浦功率和等离子距离是稳定的。