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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458 μJ、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.
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关键词:
- 超强激光与等离子体相互作用 /
- 强太赫兹辐射 /
- 相干渡越辐射
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 laser-to-THz conversion efficiency increase nonlinearly with the laser energy increasing. At maximum laser energy ~270 mJ, the measured THz pulse energy is 458 μJ, 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.-
Keywords:
- ultraintense laser-plasma interaction /
- strong terahertz radiation /
- coherent transition radiation
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图 2 太赫兹能量与激光能量及激光背向散射光的关系 (a) 太赫兹能量(红色方块)和激光-太赫兹能量转换率(蓝色方块)随激光能量的变化; (b) 不同激光能量下的背向散射光光谱
Fig. 2. Relationship between THz energy, laser energy and laser back scattered light: (a) Dependence of THz energy (red square) and THz-laser efficiency (blue square) on the laser energy; (b) laser back scattered light spectra at different laser energy.
图 3 太赫兹能量、激光光强及激光背向散射光与激光离焦量的关系 (a) 太赫兹能量(红色圆点)和激光光强(黑色方块)随激光离焦量D的变化; (b) 不同离焦量对应的激光散射光光谱
Fig. 3. Relationship between THz energy, laser intensity, laser back scattered light, and laser defocus: (a) THz energy (red dot) and laser intensity (black square) as a function of the laser defocus distance D; (b) laser back scattered light spectra at different laser defocus distance.
图 4 太赫兹频谱、偏振及光斑表征 (a) 使用带通滤片测得的太赫兹频谱(棕色方块)以及根据CTR理论使用实验参数拟合得到的理论频谱(黑色实线); (b) 使用太赫兹偏振片测得的太赫兹偏振分布; (c) 使用太赫兹相机测得的太赫兹光斑(左), 旋转相机阵面90°后测得的太赫兹光斑(右), 图中黄色箭头为太赫兹相机偏振敏感方向
Fig. 4. Characterization of THz spectrum, polarization and profile: (a) THz spectrum measured by band-pass filters (brown square) and fitted with the CTR theory (black line); (b) THz polarization distribution measured by a THz polarizer; (c) THz spot profile measured by a THz camera.
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[1] Dhillon S S, Vitiello M S, Linfield E H, et al. 2017 J. Phys. D: Appl. Phys. 50 043001
Google Scholar
[2] Liu M, Hwang H Y, Tao H, Strikwerda A C, Fan K, Keiser G R, Sternbach A J, West K G, Kittiwatanakul S, Lu J, Wolf S A, Omenetto F G, Zhang X, Nelson K A, Averitt R D 2012 Nature 487 345
Google Scholar
[3] LaRue J L, Katayama T, Lindenberg A, Fisher A S, Ostrom H, Nilsson A, Ogasawara H 2015 Phys. Rev. Lett. 115 036103
Google Scholar
[4] Zhao L R, Tang H, Lu C, Jiang T, Zhu P F, Hu L, Song W, Wang H D, Qiu J Q, Jing C G, Antipov S, Xiang D, Zhang J 2020 Phys. Rev. Lett. 124 054802
Google Scholar
[5] Wu Z, Fisher A S, Goodfellow J, Fuchs M, Daranciang D, Hogan M, Loos H, Lindenberg A 2013 Rev. Sci. Instrum. 84 022701
Google Scholar
[6] Zhang B, Ma Z, Ma J, Wu X, Ouyang C, Kong D, Hong T, Wang X, Yang P, Chen L, Li Y, Zhang J 2021 Laser Photon. Rev. 15 2000295
[7] Vicario C, Ovchinnikov A V, Ashitkov S I, Agranat M B, Fortov V E, Hauri C P 2014 Opt. Lett. 39 6632
Google Scholar
[8] Gonsalves A J, Nakamura K, Daniels J, et al. 2019 Phys. Rev. Lett. 122 084801
Google Scholar
[9] Liao G Q, Liu H, Scott G G, et al. 2020 Phys. Rev. X 10 031062
[10] Gopal A, Singh P, Herzer S, Reinhard A, Schmidt A, Dillner U, May T, Meyer H G, Ziegler W, Paulus G G 2013 Opt. Lett. 38 4705
Google Scholar
[11] Zeng Y S, Zhou C L, Song L W, Lu X M, Li Z P, Ding Y Y, Bai Y F, Xu Y, Leng Y X, Tian Y, Liu J S, Li R X, Xu Z Z 2020 Opt. Express 28 15258
Google Scholar
[12] Liao G Q, Li Y T, Li C, et al. 2015 Phys. Rev. Lett. 114 255001
Google Scholar
[13] Liao G Q, Li Y T, Zhang Y H, et al. 2016 Phys. Rev. Lett. 116 205003
Google Scholar
[14] Liao G, Li Y, Liu H, Scott G G, Neely D, Zhang Y, Zhu B, Zhang Z, Armstrong C, Zemaityte E, Bradford P, Huggard P G, Rusby D R, McKenna P, Brenner C M, Woolsey N C, Wang W, Sheng Z, Zhang J 2019 Proc. Natl. Acad. Sci. U.S.A. 116 3994
Google Scholar
[15] Woldegeorgis A, Herzer S, Almassarani M, Marathapalli S, Gopal A 2019 Phys. Rev. E 100 053204
Google Scholar
[16] Zhang J, Li Y T, Sheng Z M, Wei Z Y, Dong Q L, Lu X 2005 Appl. Phys. B 80 957
[17] Gaeta A L 2000 Phys. Rev. Lett. 84 3582
Google Scholar
[18] Haines M G, Wei M S, Beg F N, Stephens R B 2009 Phys. Rev. Lett. 102 045008
Google Scholar
[19] Schroeder C B, Esarey E, van Tilborg J, Leemans W P 2004 Phys. Rev. E 69 016501
Google Scholar
[20] Casalbuoni S, Schlarb H, Schmidt B, Schmüser P, Steffen B, Winter A 2008 Phys. Rev. Spec. Top. Accel. Beams 11 072802
Google Scholar
[21] Liu H, Liao G Q, Zhang Y H, et al. 2019 High Power Laser Sci. Eng. 7 e6 7
Google Scholar
[22] Zheng J, Tanaka K A, Miyakoshi T, Kitagawa Y, Kodama R, Kurahashi T, Yamanaka T 2003 Phys. Plasmas 10 2994
Google Scholar
[23] Gopal A, May T, Herzer S, et al. 2012 New J. Phys. 14 083012
Google Scholar
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