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-Generation of high-power, tunable terahertz radiation from laser interaction with a relativistic electron beam

Zhen Zhang, Lixin Yan, Yingchao Du, Wenhui Huang, Chuanxiang Tang, and Zhirong Huang

https://journals.aps.org/prab/abstract/10.1103/PhysRevAccelBeams.20.050701

We propose a method based on the slice energy spread modulation to generate strong subpicosecond density bunching in high-intensity relativistic electron beams. A laser pulse with periodic intensity envelope is used to modulate the slice energy spread of the electron beam, which can then be converted into density modulation after a dispersive section. It is found that the double-horn slice energy distribution of the electron beam induced by the laser modulation is very effective to increase the density bunching. Since the modulation is performed on a relativistic electron beam, the process does not suffer from strong space charge force or coupling between phase spaces, so that it is straightforward to preserve the beam quality for terahertz (THz) radiation and other applications. We show in both theory and simulations that the tunable radiation from the beam can cover the frequency range of 1–10 THz with high power and narrow-band spectra.

• 
• 
• 
• 
• 
• 
• 

Abstract-Monitoring of electron bunch length by using Terahertz coherent transition radiation

• Xiaolu Su, 
• Lixin Yan, 
• Yingchao Du, 
• Zhen Zhang, 
• Zheng Zhou, 
• Dong Wang, 
• Lianmin Zheng, 
• Qili Tian, 
• Wenhui Huang, 
• Chuanxiang Tang

• Department of Engineering Physics, Tsinghua University, Beijing, China
• Key Laboratory of Particle and Radiation Imaging (Tsinghua University), Ministry of Education, Beijing, China
• 
  

http://www.sciencedirect.com/science/article/pii/S0168583X17302550

In this paper, ultrashort bunch length monitoring was demonstrated based on Terahertz (THz) coherent transition radiation (CTR) in Tsinghua Thomson scattering X-ray (TTX) source. The radiation produced by electron bunch is split into three paths: one of them is used to detect the total energy, while the other two paths are filtered with different THz band-pass filters before detection. The bunch length variation can be obtained by calculating the ratio between the filtered energy and the total energy. The bunch is compressed by a chicane and via changing the current of chicane, the ratio of filtered energy and total energy changed correspondingly. It is a simple supplemental approach to monitor the bunch length during beam conditioning and facility operation. Bunch arrival-time jitter and nonlinear effects in chicane are observed in the experiment during the measurement of filtered energy and total energy.

Abstract-Generation of High-Power, Tunable Terahertz Radiation from Laser Interaction with a Relativistic Electron Beam

Zhen Zhang, Lixin Yan, Yingchao Du, Wenhui Huang, Chuanxiang Tang, Zhirong Huang

(Submitted on 22 Feb 2017)

https://arxiv.org/abs/1702.06653

We propose a method based on the slice energy spread modulation to generate strong subpicoseond density bunching in high-intensity relativistic electron beams. A laser pulse with periodic intensity envelope is used to modulate the slice energy spread of the electron beam, which can then be converted into density modulation after a dispersive section. It is found that the double-horn slice energy distribution of the electron beam induced by the laser modulation is very effective to increase the density bunching. Since the modulation is performed on a relativistic electron beam, the process does not suffer from strong space charge force or coupling between phase spaces, so that it is straightforward to preserve the beam quality for further applications, such as terahertz (THz) radiation and resonant excitation of plasma wakefield. We show in both theory and simulations that the tunable radiation from the beam can cover the frequency range of 1-10 THz with high power and narrow-band spectra.

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.