Efficient generation of relativistic near-single-cycle mid-infrared pulses in plasmas

Zhu, Xing-Long and Weng, Su-Ming and Chen, Min and Sheng, Zheng-Ming and Zhang, Jie (2020) Efficient generation of relativistic near-single-cycle mid-infrared pulses in plasmas. Light: Science & Applications, 9. 46. ISSN 2047-7538 (https://doi.org/10.1038/s41377-020-0282-3)

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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.