Abstract-Towards terawatt-scale spectrally-tunable terahertz pulses via relativistic laser-foil interactions

Guo-Qian Liao, Hao Liu, Graeme G. Scott, Yi-Hang Zhang, Bao-Jun Zhu, Zhe Zhang, Yu-Tong Li, Chris Armstrong, Egle Zemaityte, Philip Bradford, Dean R. Rusby, David Neely, Peter G. Huggard, Paul McKenna, Ceri M. Brenner, Nigel C. Woolsey, Wei-Min Wang, Zheng-Ming Sheng, Jie Zhang

https://journals.aps.org/prx/accepted/f9077Ka7Ta61f80ac4557eb8820820c019e7c6ab0

An ever-increasing number of strong-field applications, like ultrafast coherent control over matter and light, require driver light pulses that are of both high power and tunable spectra. However, the realization of such a source in the terahertz (THz) band has long been a formidable challenge. Here, we demonstrate, via experiment and theory, the efficient production of terawatt (TW)-level THz pulses from high-intensity picosecond laser irradiation on a metal foil. The THz spectra can be manipulated effectively by tuning the laser pulse duration or target size. An analytical model that well reproduces the experimental results is developed, and the spectral tunability stems from a hybrid THz generation mechanism driven jointly by both the high-current electron emission and the time-varying electron sheath at the target rear. In addition to being an ultrabright source (brightness temperature ~10^21 K) for extreme THz science, the THz radiation presented here also enables a unique in-situ laser-plasma diagnostic, and it has been employed to quantify the escaping electrons and the transient sheath, in good agreement with experimental measurements.

Abstract-Multimillijoule coherent terahertz bursts from picosecond laser-irradiated metal foils

Guoqian Liao, Yutong Li, Hao Liu, Graeme G. Scott, David Neely, Yihang Zhang, Baojun Zhu, Zhe Zhang, Chris Armstrong, Egle Zemaityte, Philip Bradford, Peter G. Huggard, Dean R. Rusby, Paul McKenna, Ceri M. Brenner, Nigel C. Woolsey, Weimin Wang, Zhengming Sheng, Jie Zhang

https://www.pnas.org/content/116/10/3994

Terahertz (THz) radiation, with frequencies spanning from 0.1 to 10 THz, has long been the most underdeveloped frequency band in electromagnetic waves, mainly due to the dearth of available high-power THz sources. Although the last decades have seen a surge of electronic and optical techniques for generating intense THz radiation, all THz sources reported until now have failed to produce above-millijoule (mJ) THz pulses. We present a THz source that enables a THz pulse energy up to tens of mJ, by using an intense laser pulse to irradiate a metal foil.

Abstract-Multimillijoule coherent terahertz bursts from picosecond laser-irradiated metal foils

Guoqian Liao, Yutong Li, Hao Liu, Graeme G. Scott, David Neely, Yihang Zhang, Baojun Zhu, Zhe Zhang, Chris Armstrong, Egle Zemaityte, Philip Bradford, Peter G. Huggard, Dean R. Rusby, Paul McKenna, Ceri M. Brenner, Nigel C. Woolsey, Weimin Wang, Zhengming Sheng, and Jie Zhang

https://www.pnas.org/content/early/2019/02/12/1815256116


Ultrahigh-power terahertz (THz) radiation sources are essential for many applications, for example, THz-wave-based compact accelerators and THz control over matter. However, to date none of the THz sources reported, whether based upon large-scale accelerators or high-power lasers, have produced THz pulses with energies above the millijoule (mJ) level. Here, we report a substantial increase in THz pulse energy, as high as tens of mJ, generated by a high-intensity, picosecond laser pulse irradiating a metal foil. A further up-scaling of THz energy by a factor of ∼4 is observed when introducing preplasmas at the target-rear side. Experimental measurements and theoretical models identify the dominant THz generation mechanism to be coherent transition radiation, induced by the laser-accelerated energetic electron bunch escaping the target. Observation of THz-field-induced carrier multiplication in high-resistivity silicon is presented as a proof-of-concept application demonstration. Such an extremely high THz energy not only triggers various nonlinear dynamics in matter, but also opens up the research era of relativistic THz optics.

Abstract-Electro-optic sampling of optical pulses and electron bunches for a compact THz-FEL source

Bang Wu, 

Zhe Zhang, 

Lei Cao,  

Qiang Fu, 

Yongqian Xiong

https://www.sciencedirect.com/science/article/pii/S1350449518302895

A systematic one dimensional analytical model describing the full electromagnetic propagation in electro-optic (EO) diagnostic is proposed and designed for a terahertz FEL source at HUST. Our model contains two main aspects: the propagation of the THz pulse (1.5–6 THz) along the transport line and the THz EO process in the detection crystal. The diffraction, Fabry–Perot and focusing effects are included in the THz propagation process. The phase mismatch, the frequency-dependent EO coupling coefficient and geometrical overlap between probe and THz pulses as well as the group velocity dispersion and finite duration of the probe pulse are considered in the THz EO process. The calculation shows that the diffraction in the TPX window and the Fabry–Perot effect in the GaP crystal are crucial for retrieving the details of the THz optical pulse. While for electron bunches, the detected Coulomb electric field will be significantly broadened due to the relatively low relativistic Lorenz factor (γ=10–20$\mathrm{}\mathrm{}$). Therefore, a convenient deconvolution algorithm is utilized to reconstruct THz electric field from the distorted EO signals, where the truncated singular value decomposition method is employed. Our algorithm is verified to work well even with a low signal-to-noise ratio (20 dB) in the future measurement.

Abstract- Terahertz Electro-Optic Sampling in Thick ZnTe Crystals Below the Reststrahlen Band With a Broadband Femtosecond Laser

Bang Wu,  Lei Cao,   Zhe Zhang,   Qiang Fu,   Yongqian Xiong

https://ieeexplore.ieee.org/document/8319525/

The method of electro-optic (EO) sampling of terahertz (THz) pulses in thick EO crystals leads to waveform distortions due to effects of phase mismatch, dispersive propagation, and absorption. In this paper, we demonstrate theoretically and experimentally that EO sampling with a broadband femtosecond (fs) laser could significantly eliminate these distortions below the Reststrahlen band. Our simulation results show that the oscillations and dips in the signals of EO response function of thick crystals are smoothed out by the broadband spectrum of the femtosecond laser. In the experiment, we use a laser with a bandwidth of 100 nm and a low temperature GaAs photoconductive antenna to generate typical THz pulses (0.1-3 THz). The measurement results confirm that a {110}-oriented 3-mm-thick ZnTe crystal is an attractive EO material for sampling THz pulse below 3 THz and agree with simulation results. This technique is particularly useful in areas where a large time window is needed, for example in the THz time-domain spectroscopy system.

Abstract-Demonstration of Coherent Terahertz Transition Radiation from Relativistic Laser-Solid Interactions

Guo-Qian Liao, Yu-Tong Li, Yi-Hang Zhang, Hao Liu, Xu-Lei Ge, Su Yang, Wen-Qing Wei, Xiao-Hui Yuan, Yan-Qing Deng, Bao-Jun Zhu, Zhe Zhang, Wei-Min Wang, Zheng-Ming Sheng, Li-Ming Chen, Xin Lu, Jing-Long Ma, Xuan Wang, and Jie Zhang

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.205003

Coherent transition radiation in the terahertz (THz) region with energies of sub-mJ/pulse has been demonstrated by relativistic laser-driven electron beams crossing the solid-vacuum boundary. Targets including mass-limited foils and layered metal-plastic targets are used to verify the radiation mechanism and characterize the radiation properties. Observations of THz emissions as a function of target parameters agree well with the formation-zone and diffraction model of transition radiation. Particle-in-cell simulations also well reproduce the observed characteristics of THz emissions. The present THz transition radiation enables not only a potential tabletop brilliant THz source, but also a novel noninvasive diagnostic for fast electron generation and transport in laser-plasma interactions.

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• Received 12 January 2016

DOI:http://dx.doi.org/10.1103/PhysRevLett.116.205003

Abstract-Demonstration of coherent terahertz transition radiation from relativistic laser-solid interactions

Guo-Qian Liao, Yu-Tong Li, Yi-Hang Zhang, Hao Liu, Xu-Lei Ge, Su Yang, Wen-Qing Wei, Xiao-Hui Yuan, Yan-Qing Deng, Bao-Jun Zhu, Zhe Zhang, Wei-Min Wang, Zheng-Ming Sheng, Li-Ming Chen, Xin Lu, Jing-Long Ma, Xuan Wang, and Jie Zhang

https://journals.aps.org/prl/accepted/64073Y26Ac61c24186100044b132eaa55a298f122

Coherent transition radiation in the terahertz (THz) region with energies of sub-mJ/pulse has been demonstrated by relativistic laser-driven electron beams crossing the solid-vacuum boundary. Targets including mass-limited foils and layered metal-plastic targets are used to verify the radiation mechanism and characterize the radiation properties. Observations of THz emissions as a function of target parameters agree well with the formation-zone and diffraction model of transition radiation. Particle-in-cell simulations also well reproduce the observed characteristics of THz emissions. The present THz transition radiation enables not only a potential tabletop brilliant THz source, but also a novel noninvasive diagnostic for fast electron generation and transport in laser-plasma interactions.