Broadband terahertz radiation can be efficiently produced by mixing laser pulses of different colors in the mid-infrared (MIR) and longwave-infrared (LWIR) spectral region. In this paper, we report on a numerical investigation of ultrashort terahertz pulse generation from plasmas created in nitrogen gas by two-color laser pulses with the fundamental laser pulse wavelength between 2.15 and 15.15 µm, in order to explore the efficiency of the terahertz pulse generation process. The results show that the electron acceleration efficiency increases monotonically with the fundamental laser pulse wavelength. The most intense terahertz pulse generation is observed at 12.30 µm with four optical-cycle laser pulses with 2.5 GW peak power. The results show that the terahertz pulse generation with a MIR laser is one order of magnitude and with a LWIR laser is two orders of magnitude more efficient than the terahertz pulse generation with Ti:Sapphire lasers using the exact same pulse parameters. The terahertz pulse generation efficiency is also known to be very sensitive to the relative phase between the components of the two-color laser pulses. One of the most useful tools to control the relative phase and optimize the terahertz pulse intensity is thin dielectric plates. It has been shown that alkaline halides and alkaline earth halides have suitable optical properties for the relative phase control for efficient terahertz pulse generation in the MIR spectral range.

中文翻译：

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红外双色激光脉冲在氮气中产生相位控制的，二次谐波优化的太赫兹脉冲

通过在中红外（MIR）和长波红外（LWIR）光谱区域混合不同颜色的激光脉冲，可以有效地产生宽带太赫兹辐射。在本文中，我们报告了由基本脉冲波长在2.15和15.15 µm之间的两种颜色的激光在氮气中产生的等离子体产生超短太赫兹脉冲的数值研究，以探索太赫兹脉冲产生的效率处理。结果表明，电子加速效率随基波激光脉冲波长单调增加。在四个峰值为2.5 GW的光周期激光脉冲下，在12.30 µm处观察到最强烈的太赫兹脉冲产生。结果表明，与使用Ti：Sapphire激光器的太赫兹脉冲生成（使用完全相同的脉冲参数）相比，MIR激光器的太赫兹脉冲生成的效率高一个数量级，而LWIR激光器的效率高出两个数量级。还已知太赫兹脉冲产生效率对双色激光脉冲的分量之间的相对相位非常敏感。薄介电板是控制相对相位并优化太赫兹脉冲强度的最有用工具之一。已经表明，碱金属卤化物和碱土金属卤化物具有合适的光学特性，用于相对相位控制，以便在MIR光谱范围内有效产生太赫兹脉冲。蓝宝石激光器使用完全相同的脉冲参数。还已知太赫兹脉冲的产生效率对双色激光脉冲的分量之间的相对相位非常敏感。薄介电板是控制相对相位并优化太赫兹脉冲强度的最有用工具之一。已经表明，碱金属卤化物和碱土金属卤化物具有合适的光学特性，用于相对相位控制，以便在MIR光谱范围内有效产生太赫兹脉冲。蓝宝石激光器使用完全相同的脉冲参数。还已知太赫兹脉冲产生效率对双色激光脉冲的分量之间的相对相位非常敏感。薄介电板是控制相对相位并优化太赫兹脉冲强度的最有用工具之一。已经表明，碱金属卤化物和碱土金属卤化物具有合适的光学特性，用于相对相位控制，以便在MIR光谱范围内有效产生太赫兹脉冲。