Abstract-Ultrafast mapping of coherent dynamics and density matrix reconstruction in a terahertz-assisted laser field

Yizhu Zhang, Tian-Min Yan, and Y. H. Jiang

https://journals.aps.org/prl/accepted/72070YfeY1813151b83985b6a2b9e1d97a95cc969

A time-resolved spectroscopic protocol exploiting terahertz-assisted photoionization is proposed to reconstruct transient density matrix. Population and coherence elements are effectively mapped onto spectrally separated peaks in photoionization spectra. The beatings of coherence dynamics can be temporally resolved beyond the pulse duration, and the relative phase between involved states is directly readable from the oscillatory spectral distribution. As demonstrated by a photo-excited multilevel open quantum system, the method shows potential applications for sub-femtosecond time-resolved measurements of coherent dynamics with free electron lasers and tabletop laser fields.

Abstract-Terahertz generation in dual-color laser: continuum electron in strong-field single-atom ionization

Kaixuan Zhang, Yizhu Zhang, T.-M. Yan, Y.H. Jiang

https://arxiv.org/abs/1805.12127

The terahertz (THz) generation in a dual-color field was investigated experimentally by precisely controlling the relative time delay τ and polarization θ of dual-color lasers, where the accompanying third-harmonic generation (THG) is employed to determine τ up to the sub-wavelength accuracy. An anticorrelation of the yields between THz and THG with τ was displayed. Compared with the theoretical simulations, the experimental results reveal that the continuum-continuum transitions of the released electron after single-atom ionization are the dominating mechanism for THz generation, which is opposite to the high-harmonic generation (HHG) based on the recollision mechanism, or the radiation induced by perturbative bound-bound transitions.

Abstract-Clue to a thorough understanding of terahertz pulse generation by femtosecond laser filamentation

Jiayu Zhao, Weiwei Liu, Shichang Li, Dan Lu, Yizhu Zhang, Yan Peng, Yiming Zhu, and Songlin Zhuang

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-6-4-296

In this work, it has been demonstrated that in order to fully understand the terahertz (THz) pulse generation process during femtosecond laser filamentation, the interaction between THz wave and air plasma has to be taken into account. This interaction is mainly associated with the spatial confinement of the THz pulse by the plasma column, which could be described by the one-dimensional negative dielectric (1DND) waveguide model. By combining the 1DND model with the conventional four-wave mixing (4WM) and photocurrent (PC) models, the variation of THz spectral amplitude and width obtained in experiments could be better understood. Finally, a three-step procedure, with 1DND bridging 4WM and PC processes, has been established for the first time to describe the underlying mechanism of THz radiation from plasma sources.

© 2018 Chinese Laser Press

Abstract-Temporal Superresolution Mapping of Ultrafast Coherent Dynamics in Terahertz-Assisted Laser Field

Yizhu Zhang, Tian-Min Yan, Y. H. Jiang

https://arxiv.org/abs/1711.06417

Quantum coherence is of potential applications from quantum computation using simple atoms to optimized energy transports in biomolecular complexes. Here, a time-resolved spectroscopic protocol exploiting a terahertz-assisted field locked with the probe pulse is proposed for full observations of the evolution of elements in transient density matrix. Coherence contributions of off-diagonal elements are detectable in the spotlight. The coherence dynamics for photoexcitation of hydrogen atom are explicitly demonstrated with significantly improved temporal resolution beyond the probe pulse duration. Present approach with improving time resolution and highlighting coherence dynamics displays potential applications for sub-femtosecond or attosecond time-resolved measurements in free electron lasers and tabletop laser fields.

Abstract-Terahertz Wave Guiding by Femtosecond Laser Filament in Air

Jiayu Zhao, Yizhu Zhang, Zhi Wang, Wei Chu, Bin Zeng, Ya Cheng, Zhizhan Xu, Weiwei Liu

http://arxiv-web3.library.cornell.edu/abs/1310.5435

(Submitted on 21 Oct 2013)

Femtosecond laser filament generates strong terahertz (THz) pulse in air. In this paper, THz pulse waveform generated by femtosecond laser filament has been experimentally investigated as a function of the length of the filament. Superluminal propagation of THz pulse has been uncovered, indicating that the filament creates a THz waveguide in air. Numerical simulation has confirmed that the waveguide is formed because of the radially non-uniform refractive index distribution inside the filament. The underlying physical mechanisms and the control techniques of this type THz pulse generation method might be revisited based on our findings. It might also potentially open a new approach for long-distance propagation of THz wave in air.