Abstract-Manipulation of polarizations for broadband terahertz waves emitted from laser plasma filaments

Zhelin Zhang, Yanping Chen, Sen Cui, Feng He, Min Chen, Zhen Zhang, Jin Yu, Liming Chen, Zhengming Sheng, Jie Zhang,

https://www.nature.com/articles/s41566-018-0238-9?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+nphoton%2Frss%2Fcurrent+%28Nature+Photonics+-+Issue%29

Polarization control of broadband terahertz waves is essential for applications in many areas, such as materials science, medical and biological diagnostics, near-field communications and public securities. Conventional methods for polarization control are limited to narrow bandwidth and often with low efficiency. Here, based on theoretical and experimental studies, we demonstrate that the two-colour laser scheme in gas plasma can provide effective control of elliptically polarized terahertz waves, including their ellipticity, azimuthal angle and chirality. This is achieved with a circularly polarized laser at the fundamental frequency and its linearly polarized second harmonic, a controlled phase difference between these two laser components, as well as a suitable length of the laser plasma filament. Flexible control of ellipticity and azimuthal angle is demonstrated with our theoretical model and systematic experiments. This offers a unique and flexible technique on the polarization control of broadband terahertz radiation suitable for a wide range of applications.

Abstract-Controllable terahertz radiation from a linear-dipole array formed by a two-color laser filament in air

Zhelin Zhang, Yanping Chen, Min Chen, Zhen Zhang, Jin Yu, Zhengming Sheng, and Jie Zhang

https://journals.aps.org/prl/accepted/fd074Y68Ied1594578cd5ca4cd2aa25a9fed8b991

We have demonstrated the effective control on carrier-envelope phase, angular distribution as well as peak intensity of a nearly single-cycle terahertz pulse emitted from a laser filament formed by two-color, the fundamental and the corresponding second harmonics, femtosecond laser pulses propagating in air. Experimentally, such control has been performed by varying the filament length and the initial phase difference between the two-color laser components. A linear-dipole-array model, including the descriptions of the both generation (via laser field ionization) and propagation of the emitted terahertz pulse, is proposed to present a quantitative interpretation of the observations. Our results contribute to the understanding of terahertz generation in a femtosecond laser filament and suggest a practical way to control the electric field of terahertz pulse for potential applications.

Abstract-Spectral interference of terahertz pulses from two laser filaments in air

Yanping Chen^1,2,a), Zhelin Zhang^1,2, Zhen Zhang^1,2, Xiaohui Yuan^1,2, Feng Liu^1,2, Min Chen^1,2, Jianqiu Xu^1,2, Jin Yu^1,3, Zhengming Sheng^1,2,4,b) and Jie Zhang^1,2
 VIEW AFFILIATIONS
a) Electronic mail: yanping.chen@sjtu.edu.cn
b) Electronic mail: zmsheng@sjtu.edu.cn
Appl. Phys. Lett. 106, 221105 (2015); http://dx.doi.org/10.1063/1.4922143

Spectral interference is experimentally demonstrated by two terahertz pulses emitting from filaments induced by two successive femtosecond laser pulses in air. Here, a leading pulse is set to be weaker than a trailing pulse and their temporal separation is larger than the pulse duration of the terahertz pulses. When the leading pulse is stronger than the trailing pulse, thefrequency modulation within the whole terahertz envelope is greatly deteriorated due tononlinear effects applying on the trailing pulse through the plasmas generated by the leading pulses. Such unique terahertz spectrum may find applications in terahertz spectroscopy.

Abstract-Dual-frequency terahertz emission from splitting filaments induced by lens tilting in air

Zhelin Zhang¹, Yanping Chen^1,a), Liu Yang¹, Xiaohui Yuan¹, Feng Liu¹, Min Chen¹, Jianqiu Xu¹, Zhengming Sheng^1,2 and Jie Zhang¹
http://scitation.aip.org/content/aip/journal/apl/105/10/10.1063/1.4895720
1 Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
2 Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom
a) Author to whom correspondence should be addressed. Electronic mail: yanping.chen@sjtu.edu.cn
Appl. Phys. Lett. 105, 101110 (2014); http://dx.doi.org/10.1063/1.4895720

Dual-frequency terahertz radiation from air-plasma filaments produced with two-color lasers in air has been demonstrated experimentally. When a focusing lens is tilted for a few degrees, it is shown that the laser filament evolves from a single one to two sub-filaments. Two independent terahertz sources emitted from the sub-filaments with different frequencies and polarizations are identified, where the frequency of terahertz waves from the trailing sub-filament is higher than that from the leading sub-filament.