Abstract-Temperature-controlled terahertz polarization conversion bandwidth

 

Jing Zhao, Chunmei Ouyang, Xieyu Chen, Yanfeng Li, Caihong Zhang, Longcheng Feng, Biaobing Jin, Jiajun Ma, Yi Liu, Shoujun Zhang, Quan Xu, Jiaguang Han,  Weili Zhang, 

Schematic diagram of the metasurface structure and experimental system. (a) Unit cell, composed of sapphire substrate, VO2 and gold SRRs layers, polyimide dielectric layer and a gold grating, with geometrical parameters h = 2000 µm, P = 80 µm, d = 200 nm, t = 35 µm, d1 = 10 µm, and d2 = 22 µm. (b) Vertical view of the unit cell. (c) Gold SRR with geometrical parameters O = 10°, O1 = 10°, C1 = 30°, and C2 = 45°. (d)-(f) Optical microscope images of the fabricated VO2 and gold SRRs, gold grating and their combined structure, respectively. (g) Sample characterization by THz-TDS.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-14-21738&id=452731

Active control of metasurfaces has attracted widespread attention because of the adjustable electromagnetic properties obtained. Here we designed and experimentally studied a dynamically controllable polarization converter in the terahertz band. By designing the structural parameters and utilizing the insulator-to-metal phase transition of vanadium dioxide and principle of current resonance, dynamic tunability of the polarization conversion function from dual-broadband (0.45∼0.77 THz and 0.97∼1.2 THz) to ultra-broadband (0.38∼1.20 THz) can be realized with a high polarization conversion ratio. The scheme proposed here can find potential applications in integrated terahertz systems, sensing, imaging and communications areas.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Dynamics of Rydberg states and terahertz waves generated in strong few-cycle laser pulses

Jinlei Liu, Jing Zhao, Yindong Huang, Xiaowei Wang, and Zengxiu Zhao

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.102.023109

Physical processes near threshold in strong-field ionization are complex owing to the important role of many intermediate states. Two typical near-threshold processes in few-cycle laser pulses, the generations of Rydberg electrons and terahertz waves, are investigated using classical trajectory Monte Carlo simulations. Mapping final energies of electrons to the tunneling coordinates, the two processes are distinguished based on the contributions from different kinds of electron trajectories, which highlights the complex interplay between the Coulomb potential and the laser field on the electron dynamics. We clarify the dependence of momentum and energy spectra on the carrier-envelope phase. We find that the optimal phases for terahertz wave generation and creation of the Rydberg state in few-cycle laser pulses are opposite. This finding can be applied to further experiments on attosecond electron dynamics.

• 
• 
• 
• 
• 
• 
• 

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-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.

• 
• 
• 
• 

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-Trajectory-based analysis of low-energy electrons and photocurrents generated in strong-field ionization

Jinlei Liu, Wenbo Chen, Bin Zhang, Jing Zhao, Jianhua Wu, Jianmin Yuan, and Zengxiu Zhao

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.90.063420

The three-dimensional classical-trajectory Monte Carlo method is employed to investigate low-energy photoelectron spectra in above-threshold ionization by strong laser fields. By connecting the tunneling coordinates with the final momentum-energy spectra, we identify the effects of the Coulomb potential on electron trajectories and the final energy spectra. In addition, we verify that the photoelectron spectra, depending on the energy region, can be controlled with a two-color laser pulse by varying the phase delay. The modulations of the electron spectra and yields as well as the generated photocurrents reveal the connections among them, which support our previous work [Phys. Rev. Lett. 109, 243002 (2012)] on terahertz wave generation from two-color laser pulses.

DOI: http://dx.doi.org/10.1103/PhysRevA.90.063420

• 
• 
• 
• 
• 
• 
• 

• Published 17 December 2014
• Received 11 November 2014

©2014 American Physical Society