Zhu Xing-Long, Weng Su-Ming, Chen Min, Sheng Zheng-Ming, Zhang Jie
1Key Laboratory for Laser Plasmas (MOE), School of Physics and Astronomy, Shanghai Jiao Tong University, 200240 Shanghai, China.
2Collaborative Innovation Center of IFSA, Shanghai Jiao Tong University, 200240 Shanghai, China.
Light Sci Appl. 2020 Mar 20;9:46. doi: 10.1038/s41377-020-0282-3. eCollection 2020.
Ultrashort intense optical pulses in the mid-infrared (mid-IR) region are very important for broad applications ranging from super-resolution spectroscopy to attosecond X-ray pulse generation and particle acceleration. However, currently, it is still difficult to produce few-cycle mid-IR pulses of relativistic intensities using standard optical techniques. Here, we propose and numerically demonstrate a novel scheme to produce these mid-IR pulses based on laser-driven plasma optical modulation. In this scheme, a plasma wake is first excited by an intense drive laser pulse in an underdense plasma, and a signal laser pulse initially at the same wavelength (1 micron) as that of the drive laser is subsequently injected into the plasma wake. The signal pulse is converted to a relativistic multi-millijoule near-single-cycle mid-IR pulse with a central wavelength of ~5 microns via frequency-downshifting, where the energy conversion efficiency is as high as approximately 30% when the drive and signal laser pulses are both at a few tens of millijoules at the beginning. Our scheme can be realized with terawatt-class kHz laser systems, which may bring new opportunities in high-field physics and ultrafast science.
中红外（mid-IR）区域的超短强激光脉冲对于从超分辨率光谱学到阿秒X射线脉冲产生以及粒子加速等广泛应用非常重要。然而，目前使用标准光学技术产生相对论强度的少周期中红外脉冲仍然很困难。在此，我们提出并通过数值模拟证明了一种基于激光驱动等离子体光学调制产生这些中红外脉冲的新方案。在该方案中，首先在欠稠密等离子体中由强驱动激光脉冲激发等离子体尾波，随后将最初与驱动激光波长相同（1微米）的信号激光脉冲注入到等离子体尾波中。通过频率下移，信号脉冲被转换为中心波长约为5微米的相对论多毫焦近单周期中红外脉冲，当驱动激光脉冲和信号激光脉冲最初都处于几十毫焦时，能量转换效率高达约30%。我们的方案可以用太瓦级千赫兹激光系统实现，这可能会在高场物理和超快科学领域带来新的机遇。
