Laser-Plasma Interactions at the Intensity Frontier: the Transition to the QED-Plasma Regime

目前的高功率激光将光聚焦到比地球表面的太阳光高出1023倍的强度。在这些极端强度下，电子会迅速从激光聚焦的任何物质中的原子中剥离，产生等离子体。然而，随着强度从今天达到的峰值(2x10^22瓦/厘米^2)增加到预计将在2017年投入使用的下一代设施(如极限光基础设施(&gt；10^23瓦/厘米^2))，这种等离子体的行为发生了戏剧性的变化。在强度为5×10~(22)W/cm~(-2)时，激光焦点中的电磁场被预测将极大地加速等离子体中的电子，使它们大量辐射伽马射线光子。这些光子可以带走如此多的能量，以至于电子的运动受到由此产生的能量损失的影响，辐射反作用力(粒子在辐射时对自己施加的力)在决定等离子体的宏观动力学方面变得非常重要。激光的电磁场如此之强，量子电动力学效应也变得重要起来。在这种情况下，辐射反作用力不再是确定性的，也就是说，我们现在只能知道电子具有给定轨迹的概率，而不是像经典图像中那样精确地知道电子的轨迹。此外，伽马射线光子可以被转换成电子-正电子对，这些对可以发射更多的光子，从而产生雪崩般的反物质，对整个等离子体的行为产生强烈的影响。辐射反应、QED效应和超相对论等离子体过程的相互作用将定义这种新的QED-等离子体体系中激光-物质相互作用的物理学，但目前人们对此知之甚少。我们将阐述激光在QED等离子体中传输和吸收的基本理论。这将为描述激光物质相互作用超越今天的强度边界进入可预见的未来提供基础理论。这一理论将被首次测量重要QED过程的速率的实验所支持。然后，这一新理论将被用来设计在实验室中产生QED等离子体的第一批实验。这一项目将在实验室中完成第一代QED等离子体，通常只在脉冲星磁层等极端天体物理环境中才能看到。

Current high-power lasers focus light to intensities up to 10^23 times higher than the intensity of sunlight at the surface of the Earth. At these extreme intensities the electrons are quickly stripped from the atoms in any matter in the laser focus, generating a plasma. However, as intensities increase from the peak reached today (2x10^22W/cm^2) to those expected to be reached on next-generation facilities such as the Extreme Light Infrastructure (>10^23W/cm^2), due to become operational by 2017, the behaviour of this plasma dramatically alters. At intensities >5x10^22W/cm^-2 the electromagnetic fields in the laser focus are predicted to accelerate the electrons in the plasma so violently that they prolifically radiate gamma-ray photons. These photons can carry away so much energy that the electron's motion is affected by the resulting energy loss and the radiation reaction force (the force the particle exerts on itself as it radiates) becomes significant in determining the plasma's macroscopic dynamics. The laser's electromagnetic fields are so strong that quantum electrodynamics effects also become important. In this case the radiation reaction force no longer behaves deterministically, i.e. instead of knowing the electron's trajectory exactly as in the classical picture, we now can only know the probability that the electron has a given trajectory. In addition, the gamma-ray photons can be converted into electron-positron pairs, these pairs can emit further photons which emit more pairs and an avalanche of antimatter production can ensue with strong consequences for the behaviour of the plasma as a whole. The interplay of radiation reaction, QED effects and ultra-relativistic plasma processes will define the physics of laser-matter interactions in this new 'QED-plasma' regime, but is currently poorly understood. We will elucidate the basic theory of laser propagation and absorption in QED-plasmas. This will provide the foundational theory describing laser matter interactions moving beyond today's intensity frontier and into the foreseeable future. This theory will be underpinned by experiments measuring the rates of the important QED processes for the first time. The new theory will then be used to design the first experiments to generate a QED plasma in the laboratory. This project will culminate in the first generation of a QED-plasma, usually only seen in extreme astrophysical environments such as pulsar magnetospheres, in the laboratory.