SULF装置中1 PW/0.1 Hz激光系统的研究进展

随着超强超短激光技术的飞速发展,世界各地许多研究机构都在争相建设台式化的拍瓦级(1 PW=1015 W)高峰值功率激光装置,台式化拍瓦级激光装置已经成为在相对论条件下研究激光-物质相互作用的重要技术手段。在激光-物质相互作用的实验研究中,激光脉冲的重复频率具有非常重要的影响。因此,发展具有较高重复频率的拍瓦级激光装置,引起了相关研究领域内科学家们的广泛关注。

上海超强超短激光实验装置(SULF)是上海科创中心建设的重大科技基础设施之一。该项目于2016年获批启动,由中国科学院上海光学精密机械研究所主要承担建设。SULF激光装置主要包括一套SULF-10 PW激光系统和一套SULF-1 PW激光系统等。其中SULF-10 PW激光系统的重复频率将为1分钟每发次,SULF-1 PW激光系统的重复频率为0.1 Hz。SULF激光装置将为极端条件材料科学研究平台(DMEC)、超快亚原子物理研究平台(USAP)和超快化学与大分子动力学研究平台(MODEC)等三大实验平台提供驱动激光。

近期发表在High Power Laser Science and Engineering的文章(Zongxin Zhang, Fenxiang Wu, Jiabing Hu, Xiaojun Yang, Jiayan Gui, Penghua Ji, Xingyan Liu, Cheng Wang, Yanqi Liu, Xiaoming Lu, Yi Xu, Yuxin Leng, Ruxin Li, Zhizhan Xu. The 1 PW/0.1 Hz laser beamline in SULF facility[J]. High Power Laser Science and Engineering, 2020, 8(1): 010000e4)中介绍了SULF装置中1 PW/0.1 Hz激光系统的建设情况及研究进展。SULF-1 PW激光系统采用传统的两级啁啾脉冲放大(Chirped pulse amplification,CPA)结构,两级CPA系统之间由一个新型的脉冲时域净化装置相连接。该脉冲净化装置可以有效地结合交叉偏振波产生技术和飞秒光参量放大技术。在SULF-1 PW激光系统中,终端放大器输出脉冲能量达到50.8 J,脉冲重复频率为0.1 Hz,放大脉冲能量稳定性为1.2% (std)。压缩后脉冲宽度可达29.6 fs,实现了较高脉冲重复频率的拍瓦级超强超短激光输出。得益于新型的脉冲时域净化技术,激光主脉冲前80 ps处的脉冲对比度可达2.5×10-11。通过对脉冲压缩器的角色散进行优化,获得了较好的聚焦光斑质量。利用f/26.5的离轴抛面镜可以实现2.7×1019 W/cm2的聚焦峰值强度。此外,SULF-1 PW激光系统还具有良好的激光指向稳定性,一小时内测得的水平方向和竖直方向的脉冲指向抖动分别为1.89 μrad (std) 和2.45 μrad (std)。SULF-1 PW激光系统良好的重复频率性能、激光稳定性能和时域对比度性能,使其在相对论条件下激光-物质相互作用的研究过程中,可以发挥非常重要的驱动作用。

SULF-1 PW激光系统目前已处于试运行阶段,可以支持开展电子/质子加速及X射线辐射等方面的实验研究。在~300 TW/0.1 Hz激光条件下,电子加速实验可以重复产生300 MeV的准单能电子,在~400 TW/0.1 Hz激光条件下,质子加速实验已经可实现14 MeV的高能质子输出。

中国科学院上海光学精密机械研究所的SULF项目团队表示,从近期的激光运行状况及物理实验结果来看, SULF-1 PW激光系统良好的激光性能以及运行可靠性已经得到前期的实验验证。在后续的工作中,激光团队将致力于进一步提升SULF-1 PW激光的时空质量。通过可编程声光调制器(AOPDF)和可变形镜(DM)的应用,有望在不久的将来实现更高的聚焦峰值强度。

SULF装置的布局图及SULF装置中1 PW/0.1 Hz激光系统的试运行照片

The 1 PW/0.1 Hz laser beamline in SULF facility

Significant advances on ultra-intense and ultra-short laser technology have led numerous laboratories around the world to develop table-top PW-class laser systems as a means of investigating laser-matter interactions in relativistic regime. The repetition rate of PW-class femtosecond lasers is an important issue for their practical applications. And the development of repetitive PW-class lasers has attracted a great attention in recent years.

Shanghai superintense ultrafast laser facility (SULF) is a large-scale scientific project located in Shanghai, China. The project was formally launched and funded in July, 2016. The SULF facility mainly consists of two laser beamlines, SULF-10 PW beamline operating at one shot per minute and SULF-1 PW beamline operating at 0.1Hz repetition rate. The SULF facility will provide repetitive PW-level and 10 PW-level laser pulses for scientific researches on dynamic of materials under extreme conditions (DMEC), ultrafast sub-atomic physics (USAP), and big molecule dynamics and extreme-fast chemistry (MODEC).

The recent progress on the 1 PW/0.1 Hz laser beamline of SULF is reported on High Power Laser Science and Engineering (Zongxin Zhang, Fenxiang Wu, Jiabing Hu, Xiaojun Yang, Jiayan Gui, Penghua Ji, Xingyan Liu, Cheng Wang, Yanqi Liu, Xiaoming Lu, Yi Xu, Yuxin Leng, Ruxin Li, Zhizhan Xu. The 1 PW/0.1 Hz laser beamline in SULF facility[J]. High Power Laser Science and Engineering, 2020, 8(1): 010000e4). The SULF-1 PW beamline is a typical double-CPA system equipped with a novel temporal filter combining the techniques of cross-polarized wave generation (XPWG) and femtosecond optical parametric ampli?cation (OPA). The SULF-1 PW beamline can generate laser pulses of 50.8 J at 0.1 Hz after the final amplifier, and the shot-to-shot energy fluctuation of the amplified pulse is as low as 1.2% (std). After compression, pulse duration of 29.6 fs is achieved, which can support a maximal peak power of 1 PW. Benefit from the large-energy and high-contrast seed pulses generated by the novel temporal filter, the contrast ratio at -80ps before the main pulse is measured to be 2.5×10-11 in the SULF-1 PW beamline. After optimization of the angular dispersion in the grating compressor, the maximal focused peak intensity may reach 2.7×1019 W/cm2 even with an f/26.5 off-axis parabolic mirror. Moreover, the horizontal and vertical angular pointing fluctuations in one hour are measured to be 1.89 μrad (std) and 2.45 μrad (std) respectively. The moderate repetition rate, the good stability and the high temporal contrast make the SULF-1 PW beamline a desirable driving laser for laser-matter interactions in relativistic regime.

The SULF-1 PW laser beamline is now in the phase of commissioning, and preliminary experiments of particle acceleration and secondary radiation have been implemented. 300 MeV quasi-monoenergetic electrons was repetitively produced under ~300 TW/0.1 Hz laser condition. Moreover, the maximum proton energy of 14 MeV was also obtained under ~400 TW/0.1 Hz laser condition.

The SULF research group from Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, comments that the progress on the preliminary experiments and the stable daily operation of the laser have demonstrated the availability of SULF-1 PW beamline. The following works would be focused on the further improvement of pulse spatial-temporal quality. By utilization of acousto-optic programmable dispersive ?lter and deformable mirror, a higher focused peak intensity can be expected in the near future.

The layout of SULF facility and the inset shows the commissioning of SULF-1 PW beamline