Abstract-Terahertz emission and optical second harmonic generation from Si surfaces

Quan Guo, Yuan Zhang, Zhi-hui Lyu, Dong-Wen Zhang, Yin-Dong Huang, Chao Meng, Zeng-Xiu Zhao, and Jian-Min Yuan

Fig. 1. (a) Optical diagram of the experimental setup. HR: high-resistance silicon; BPF: band pass filter (@400±$\pm$10 𝑛𝑚$nm$); P: polarizer; PMT: photomultiplier tube; WP: Wollaston prism. (b) Sketch of a Si (001) sample. 𝜃$\theta$ is the angle of incidence and 𝜙$\varphi$ is the azimuthal angle of the samples.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-9-5-2376

We study polarity reversal in terahertz pulses generated from p-doped Si(001) surfaces with different doping levels. The azimuthal dependence of both terahertz emission and second-harmonic generation caused by the bulk electric quadrupole and magnetic dipole process is measured to determine the contributions of optical rectification and the surface depletion field direction, respectively. By comparing the penetration depth of the excitation laser and the depletion field strength on Si surfaces, we show that competition between the photo-Dember effect and surface field accelerations causes the polarity reversal.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Filament characterization via resonance absorption of terahertz wave

Physics of Plasmas

Zhigang Zheng,   Yindong Huang.  Quan Guo, Chao Meng, Zhihui Lü, Xiaowei Wang, Jing Zhao, Congsen Meng,  Dongwen Zhang,   Jianmin Yuan, Zengxiu Zhao,

http://aip.scitation.org/doi/abs/10.1063/1.5004551

In this work, we characterize the transmission properties of the focusing-laser-induced filament by using terahertz (THz) time domain spectroscopy. Significant resonance absorption of the THz wave is identified, which is attributed to the dynamic screening of the ionized electrons. The polarization and intensity of the filament-generated pulse have been varied to study their influences on the resonance absorption. Our results suggest that the electron density of the filament can be determined by fitting the phase shifts and absorption properties around the absorption. This method provides not only an alternative to the plasma diagnostics with plasma frequency at the THz range, but also a supplement to the existing generation theory of THz waves from plasma.

Abstract-In situ spatial mapping of Gouy phase slip with terahertz generation in two-color field

Chao Meng, Zhihui Lü, Yindong Huang, Xiaowei Wang, Wenbo Chen, Dongwen Zhang, Zengxiu Zhao, and Jianmin Yuan
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-11-12301

We establish a one-to-one mapping between the local phase slip and the spatial position near the focus by scanning a thin jet along the propagation direction of laser beams. The measurement shows that the optimal phase of terahertz can be utilized to characterize in situ the spatially dependent relative phase of the two-color field. We also investigate the role of the Gouy phase shift on terahertz generation from two-color laser-induced plasma. The result is of critical importance for phase-dependent applications of two-color laser-field, including high-order harmonic and terahertz generation.

© 2016 Optical Society of America

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Abstract-Theoretical study of terahertz generation from atoms and aligned molecules driven by two-color laser fields

Wenbo Chen, Yindong Huang, Chao Meng, Jinlei Liu, Zhaoyan Zhou, Dongwen Zhang, Jianmin Yuan, and Zengxiu Zhao

http://journals.aps.org/pra/abstract/10.1103/PhysRevA.92.033410

We study the generation of terahertz radiation from atoms and molecules driven by an ultrashort fundamental laser and its second-harmonic field by solving the time-dependent Schrödinger equation (TDSE). The comparisons between one-, two-, and three-dimensional TDSE numerical simulations show that the initial ionized wave packet and its subsequent acceleration in the laser field and rescattering with long-range Coulomb potential play key roles. We also present the dependence of the optimum phase delay and yield of terahertz radiation on the laser intensity, wavelength, duration, and ratio of two-color laser components. Terahertz wave generation from model hydrogen molecules is further investigated by comparing with high harmonic emission. It is found that the terahertz yield follows the alignment dependence of the ionization rate, while the optimal two-color phase delays vary by a small amount when the alignment angle changes from 0 to 90 degrees, which reflects the alignment dependence of attosecond electron dynamics. Finally, we show that terahertz emission might be used to clarify the origin of interference in high harmonic generation from aligned molecules by coincidentally measuring the alignment-dependent THz yields.

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Abstract-Joint Measurements of Terahertz Wave Generation and High-Harmonic Generation from Aligned Nitrogen Molecules Reveal Angle-Resolved Molecular Structures

 Huang, Chao Meng, Xiaowei Wang, Zhihui Lü, Dongwen Zhang, Wenbo Chen, Jing Zhao, Jianmin Yuan, and Zengxiu Zhao

Phys. Rev. Lett. 115, 123002 – Published 18 September 2015Yyy

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.123002

We report the synchronized measurements of terahertz wave generation and high-harmonic generation from aligned nitrogen molecules in dual-color laser fields. Both yields are found to be alignment dependent, showing the importance of molecular structures in the generation processes. By calibrating the angular ionization rates with the terahertz yields, we present a new way of retrieving the angular differential photoionization cross section (PICS) from the harmonic signals which avoids specific model calculations or separate measurements of the alignment-dependent ionization rates. The measured PICS is found to be consistent with theoretical predications, although some discrepancies exist. This all-optical method provides a new alternative for investigating molecular structures.

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Abstract-Angle-resolved molecular structures joint measurements of terahertz wave generation and high-harmonic generation from aligned nitrogen molecules

Yindong Huang, Chao Meng, Xiaowei Wang, Zhihui Lü, Dongwen Zhang, Wenbo Chen, Jing Zhao, Jianmin Yuan, and Zengxiu Zhao
http://journals.aps.org/prl/accepted/8b07bY7fR571e35ca57638920f6d60e26b623e2e8

We report the synchronized measurements of terahertz wave generation and high harmonic generation from aligned nitrogen molecules in dual-color laser fields. Both yields are found alignment-dependent showing the importance of molecular structures in the generation processes. By calibrating the angular ionization rates with the THz yields, we present a new way to retrieve the angular differential photoionization cross section (PICS) from the harmonic signals, which avoids specific model calculations or separate measurements of the alignment-dependent ionization rates. The measured PICS is found consistent with theoretical predications, although some discrepancies exist. This all-optical method provides a new alternative to investigate molecular structures.

Abstract -Attosecond synchronization of terahertz wave and high-harmonics

Zhihui Lü, Dongwen Zhang, Chao Meng, Xiyu Du, Zhaoyan Zhou, Yindong Huang, Zengxiu Zhao and Jianmin Yuan
Hide affiliations

zhao.zengxiu@gmail.com jmyuan@nudt.edu.cn
Department of Physics, National University of Defense Technology, Changsha 410073, People's Republic of China 

http://m.iopscience.iop.org/0953-4075/46/15/155602/

Argon atom ionizing in the ultrafast two-colour field has been used to investigate the physical mechanism of terahertz (THz) generation. We measured simultaneously pulse energies of THz and high-harmonics as the phase delay between the fundamental and its second harmonic was varied. The optimal phase delay of THz generation is determined according to the inherent attochirp of the emitted high-harmonics. The dynamic analysis of the tunnelling electron wave packet driven by the Coulomb–laser coupling shows that laser-assisted soft collisions of the electron wave packet with the atomic core play a key role. It is demonstrated that the rescattering process, being indispensable in high-harmonic generation processes, dominates THz wave generation as well in a more elaborate way.

Abstract-Synchronizing Terahertz Wave Generation with Attosecond Bursts

Dongwen Zhang, Zhihui Lü, Chao Meng, Xiyu Du, Zhaoyan Zhou, Zengxiu Zhao^*, and Jianmin Yuan^† 
Department of Physics, National University of Defense Technology, Changsha 410073, People’s Republic of China

We perform a joint measurement of terahertz waves and high-harmonics generated from argon atoms driven by a fundamental laser pulse and its second harmonic. By correlating their dependence on the phase delay between the two pulses, we determine the generation of THz waves in tens of attoseconds precision. Compared with simulations and models, we find that the laser-assisted soft collision of the electron wave packet with the atomic core plays a key role. It is demonstrated that the rescattering process, being indispensable in high-harmonic generation processes, dominates THz wave generation as well in a more elaborate way. The new finding might be helpful for the full characterization of the rescattering dynamics.

Abstract-Ticking terahertz wave generation in attoseconds

http://arxiv.org/abs/1206.6256

Dongwen Zhang, Zhihui Lü, Chao Meng, Xiyu Du, Zhaoyan Zhou, Zengxiu Zhao, Jianmin Yuan

(Submitted on 27 Jun 2012)

We perform a joint measurement of terahertz waves and high-order harmonics generated from noble atoms driven by a fundamental laser pulse and its second harmonic. By correlating their dependence on the phase-delay of the two pulses, we determine the generation of THz waves in tens of attoseconds precision. Compared with simulations and models, we find that the laser-assisted soft-collision of the electron wave packet with the atomic core plays a key role. It is demonstrated that the rescattering process, being indispensable in HHG processes, dominant THz wave generation as well but in a more elaborate way. The new finding might be helpful for the full characterization of the rescattering dynamics.

Comments:	4 figures
Subjects:	Atomic Physics (physics.atom-ph)
Cite as:	arXiv:1206.6256v1 [physics.atom-ph]