飞秒超强激光驱动太赫兹辐射特性的实验研究

强太赫兹源是太赫兹科学技术发展的关键,其中大能量强场太赫兹脉冲源在超快物态调控、新型电子加速器等领域具有重要的应用前景.超快超强激光与等离子体相互作用是近年来发展起来的一种新型的强场太赫兹辐射产生途径.本文报道了利用超强飞秒激光脉冲与金属薄膜靶作用产生太赫兹辐射的实验结果,研究了激光能量和离焦量对靶后太赫兹辐射能量的影响,并通过监测激光背向散射光谱,定性揭示了其变化规律与不同光强下的电子加热机制的相关性.实验表征了太赫兹辐射的频谱、偏振及聚焦光斑情况.测量结果表明,实验产生了脉冲能量达458μJ、聚焦场强高达GV/m量级的超宽带太赫兹辐射,为开展极端太赫兹脉冲与物质相互作用研究提供了一种新的强场太赫兹光源.

Experimental study of terahertz radiation driven by femtosecond ultraintense laser

Powerful terahertz(THz)radiation sources are crucial to the development of THz science.High-energy strong-field THz pulses have many significant applications such as in the ultrafast control of matter and the THz-driven electron acceleration.In recent years,ultraintense laser-plasma interactions have been proposed as a novel approach to strong-field THz generation.In this paper,the experimental results are presented about the generation of THz radiation from a solid foil irradiated by a 10-TW femtosecond laser pulse.The THz energy as a function of laser energy and defocusing amount is studied.It is found that both the THz energy and the laserto-THz conversion efficiency increase nonlinearly with the laser energy increasing.At maximum laser energy~270 mJ,the measured THz pulse energy is 458μJ,corresponding to a laser-to-THz energy conversion efficiency of 0.17%.No indication of saturation is observed in the experiment,implying that a stronger THz radiation could be achieved with higher laser energy.By simultaneously monitoring the backward scattered laser light spectrum,it is qualitatively understood that the observed THz radiation as a function of laser energy and laser defocusing distance is closely related to the electron heating mechanisms at different laser intensities.The THz spectrum and polarization are characterized by using different band-pass filers and a wire-grid polarizer,respectively.The THz radiation covers an ultrabroad band ranging from 0.2 THz to 30 THz,and shows a radially polarized distribution.By fitting the measured THz spectrum with the theory of coherent transition radiation,the THz pulse duration is inferred to be about 30 fs.At the THz focal spot of~1 mm in size,the THz field strength is evaluated to be 3.68 GV/m.Such a strong-field THz source will enable the study of extreme THz-matter interactions.