Abstract-Enhance terahertz radiation and its polarization- control with two paralleled filaments pumped by two-color femtosecond laser fields

 

Qiying Song, Xinming Yuan, Saisai Hu, Jiefeng Huang, Haizhe Zhong, Qinggang Lin, Honggeng Wang, Xiaowei Lu, Maijie Zheng, Yi Cai, Xuanke Zeng,  Shixiang Xu, 

 (a) Schematic diagram of the experimental apparatus. DWP: zero-order dual-wavelength wave plate (1/2 wave for 800 nm and full wave for 400 nm); HWP1,2,3: half-wave plate of fundamental wave; QWP: quarter-wave plate of fundamental wave; α-BBO: alpha-barium borate crystal; β-BBO: beta-barium borate crystal; BS1, BS2: beam splitters; PM: parabolic mirror; Spec: spectrometer; DS: delay stage; the THz detector system contains a pair of PMs, silicon wafer, Teflon plate and Golay cell. (b) The measured power of THz radiation as function of the power of a two-color laser field with different focal length.

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We present experimentally an obvious enhancement of the terahertz (THz) radiation with two paralleled filaments pumped by two-color laser fields for a full use of a high laser power, compared with single filament. By mapping the 3-dimensional electric trajectories of generated THz fields with a (111) ZnTe crystal, we observe that the total THz polarization from two filaments can be manipulated by varying the time delay between the two orthogonally polarized pumps, which agrees well with the simulations under the photocurrent model. Notably, the power and spectrum of the THz field almost keep unchanged while manipulating the ellipticity of the THz polarization, which is important for a polarization-controllable THz source.

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