面向艾瓦(EW)飞秒超强激光的新机制研究

Prospects for femtosecond ultrahigh intensity laser system towards Exawatt level

自1985年Mourou教授提出啁啾脉冲放大(CAP)技术以来,人们在实验室台面上实现太瓦(TW,10^(12)W)乃至拍瓦(PW,10^(15)W)量级峰值功率的激光成为可能.经过三十多年的发展,世界上已有数个研究组实现了台面PW峰值功率的激光输出.国内中国科学院物理研究所、上海光学精密机械研究所、中国工程物理研究院激光聚变研究中心等单位在多年CPA及OPCPA技术的研究基础上,自2010年以来也相继产生了超过1 PW的结果.由于激光聚变(ICF)、等离子体物理、天体物理、激光粒子加速以及新光源对激光强度的需求,未来超强激光有望做到艾瓦(EW,10^(18)W)甚至更高峰值功率的输出.然而,在CPA机制下要获得更高的超强激光,就要求更大的光束口径、更高质量的激光介质以及米级以上的压缩光栅.加工制造出光学均匀性和精度满足要求的这些光学元件,工程上将面临许多挑战性的问题.本文结合我们正在开展的超快超强激光研究,通过广泛调研,分析展望了可实现EW激光输出的方法与机制,认为在等离子体中进行受激背向散射放大和脉冲压缩有望实现EW激光输出.

The new generation system for ultrahigh-power laser running over Exawatt （EW, 1018 W） level is emerging recently, which is under a mechanism called Raman backscattering （RBS） in plasma. The main advantage of using plasma is that it can tolerate much higher laser intensities, 1017 W cm a, more than five order of solid-state devices limited, 10^12 W cm 2. Although Petawatt （PW, 10^15 W） laser pulses have been realized by some groups based on the chirped pulse amplification scheme （CPA）, many cutting-edge scientific researches and technical applications, such as inertial confinement fusion （ICF）, plasma physics, astrophysics, plasma-based particle accelerators, and X-ray lasers, need even higher laser power than EW level. For these purposes, huge laser projects like the extreme light infrastructure （ELI） have been proposed to offer new paradigm in EW class laser power. However, such an ultrahigh intensity laser system could only be achieved by CPA using very large （beyond l m2） and expensive compressor gratings. In addition, to extrapolate CPA to the EW power range, hundreds of such gratings would be required. Even if there is enough budget, the problem of energy restriction on the last grating is still under question. Therefore, it is crucial to find a new mediltm or new technology for generating femtosecond ultra-intense laser pulses. This paper introduces a solution for generating laser intensities many orders of magnitude higher than currently results. This technology of optical amplification that a process known as Raman backscattering amplification and compression could enable the generation of femtosecond pulses of 20000 times the original seed intensity in a column of plasma just a few millimeters in length and less than a millimeter in width, without stretcher and compressor. Such sufficient high intensity and lower frequency of the pulse amplification indeed have got into super-radiant amplification regime （SRA） or stimulated Raman backscattering （SRBS）. It has revealed that an unprecedented large pulse intensity amplification could be realized. The seed pulse will be compressed to 25 fs and its unfocused intensity increased from 1 × 10^15 to 4x 10^17 W cm^-2. Furthermore, it could be increased further to around 1×10^23 W cm 2 by focusing the resulting beam to 1 jam. Therefore, it might be possible to increase this power up to EW in a larger plasma and using more powerful optical pumping.