Observation of the Terahertz Pulse Shaping Due to Intensity-Induced Additional Phase in Two-Color Filaments
Observation of the Terahertz Pulse Shaping Due to Intensity-Induced Additional Phase in Two-Color Filaments
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DOI：
10.1007/s10762-021-00797-4
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发表时间：
2021-06
期刊：
影响因子：
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通讯作者：
C. Gong;T. Teramoto;M. Tonouchi
中科院分区：
文献类型：
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作者：
C. Gong;T. Teramoto;M. Tonouchi
作为一种有前途的太赫兹（THz）源，气体中的双色激光成丝引起了指数级增长的兴趣，因为输出太赫兹脉冲能量和带宽随输入参数的可扩展性。然而，激光灯丝内对太赫兹脉冲生成过程的非线性影响，例如强度相关的折射率变化引起的附加相位，从未得到深入研究。在本文中，我们通过空气偏置相干探测（ABCD）采样装置记录了 1.75 ~ 2.75 mJ 输入红外泵浦能量，实验研究了太赫兹波形演化。我们观察到正负峰的幅值比随着泵浦脉冲能量的增加而增加，尾部的平滑峰逐渐消失。基于光电流模型，我们的计算表明，调制是由等离子体引起的附加相位随入射激光强度的变化而引起的。另外，尾部的平滑峰值被认为是由负峰值之后的剩余电流衰落引起的。
As a promising terahertz (THz) source, two-color laser filamentation in gases attracts an exponential growth of interest because of the scalability of output THz pulse energy and bandwidth with input parameters. However, nonlinear effects within the laser filament on the THz pulse generation process, such as intensity-dependent refractive index change induced additional phase, have never been studied in depth. In this paper, we experimentally investigate the THz waveform evolution with input infrared pump energy from 1.75 ~ 2.75 mJ were recorded by an air biased coherent detection (ABCD) sampling setup. We observe that the magnitude ratio of the positive and negative peaks increases with the pump pulse energy, and the smooth peak at the tail gradually disappears. Based on the photocurrent model, our calculation shows that the modulation is caused by the plasma-induced additional phase that varies with incident laser intensity. Additionally, the smooth peak at the tail is considered to be caused by the fading of the residual current after the negative peak.