Abstract-Numerical simulation on terahertz wave propagation in plasma channels

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Dan Lua, Hui Gao, Jiayu Zhao, Bo Yang, Weiwei 
Liu, https://www.sciencedirect.com/science/article/pii/S0030402619300075

Terahertz (THz) wave generated by femtosecond laser filamentation can spatially constrained inside the plasma channels. Our simulation results show that this constraint to THz wave will gradually weaken with the increasing THz frequency. At the same time, results also indicate that the higher plasma density possesses the stronger constraint. In addition, the model field radius and width of THz wave will become larger with the increasing plasma channel radius. Based on the simulation results we find the changes of refractive index at THz wave play an important role on THz wave propagation in plasma channels.

Abstract-Investigating the non-radially polarized component of terahertz wave emission during single-colour femtosecond laser filamentation in air

Jiayu Zhao, Hui Gao, Shichang Li, Chang Liu, Yamin Chen, Yan Peng,  Yiming Zhu

http://iopscience.iop.org/article/10.1088/2040-8986/aadef7/pdf

Recently, simultaneous emission of radially and non-radially polarized terahertz (THz) pulses during single-colour femtosecond laser filamentation has been reported. In this work, the latter radiation has been specifically investigated, instead of the well-studied THz radial polarization. Briefly, cut-back measurements have verified that the ellipticity of the generated THz pulse with non-radial polarization decreased (became more linearly polarized) with the increasing filament length. The underlying mechanism responsible for this phenomenon is the existence of a propagation effect of THz wave along the filament plasma channel. In this case, the resulted off-axis propagation of THz wave inside the plasma column played a dominant role on the generated non-radial THz polarization, rather than the expected on-axis THz birefringence induced by the high laser intensity. This discovery will greatly renew the understanding of THz emission from plasma sources.

Abstract-A simple method to enhance terahertz radiation from femtosecond laser filament array with a step phase plate

Jiayu Zhao, Lanjun Guo, Wei Chu, Bin Zeng, Hui Gao, Weiwei Liu, and Ya Chen
https://www.osapublishing.org/ol/upcoming_pdf.cfm?id=236756

• Abstract: In this work, we experimentally demonstrate a 200% enhancement of terahertz (THz) wave amplitude generated by femtosecond laser filamentation in air. The experimental setup simply uses a semicircular phase plate to generate two parallel filaments. Temporally overlapped THz pulses from two filaments coherently add up, giving rise to significant enhancement of the THz pulse amplitude. It has been foreseen that further enhancement would be achieved if the design of phase plates could be optimized to generate filament array. This simple method makes full use of the laser energy and might potentially open a new approach to remotely enhance the THz emission in air.