Saturday, August 1, 2020

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

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.

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