Armoured: Atomic R-matrix Method For Relativistic Dynamics

为了“观察”原子中的电子，我们需要能够在与相互作用本身相当的时间尺度上描述它们的运动。这类似于拍照——物体移动得越快，捕捉它所需的曝光时间就越短。谐波产生的过程——一个原子中的电子在激光场的驱动下以这样一种方式重新发射激光的高谐波——为探测原子和分子结构提供了一种独特的工具——允许分子轨道成像，甚至化学反应发生的视频。虽然这个领域的阿秒物理学（1阿秒=十亿分之一秒的十亿分之一）是很好的建立，理论描述和计算模型的基本过程是不发达的。为了充分描述原子中激光驱动电子的基本动力学，我们不仅需要考虑激光场的效应，甚至不仅仅是电子的净效应，我们还必须描述许多电子之间复杂的相互作用。为了以一种计算上易于处理的方式促进这种描述，我们开发了时变r矩阵理论（TDRM）和相关的计算机代码。该理论利用构型空间的r矩阵划分，以简化计算而不忽略重要的多电子效应。我们打算扩展TDRM技术来描述超快过程中的相对论效应。自旋轨道相互作用，其中电子的本征（自旋）和轨道角动量干涉改变其行为，引起原子能级的精细结构分裂。电子在这些能级之间的跃迁发生在一个由能隙控制的时间尺度上。对于更重的元素，如氪和氙，这个时间尺度大约是几飞秒，因此动力学可以在激光脉冲内演变。通过开辟新的电子发射通道和改变电子跃迁的选择规则，自旋轨道效应可以显著改变阿秒物理的基本过程——电离、谐波产生等。因此，在原子尺度上可以观察到有趣的新动力学。通过使用TDRM方法，我们将能够从第一性原理对这些动力学进行建模，从而对原子科学中一些最基本的物理过程提供无与伦比的见解。

In order to 'view' electrons in the atom, we need to be able to describe their motion on a time-scale comparable to the interactions themselves. This is akin to taking a photograph- the faster an object is moving, the shorter the exposure time required to capture it. The process of harmonic generation- where an electron in an atom is driven by a laser field in such a way as it re-emits high harmonics of the laser light- has provided a unique tool for probing atomic and molecular structure- allowing the imaging of molecular orbitals and even videos of chemical reactions taking place. While this field of attosecond physics (1 attosecond = 1 billionth of a billionth of a second) is well established, the theoretical description and computational models of the underlying processes are underdeveloped.In order to fully describe the fundamental dynamics of laser driven electrons in the atom we need to consider not just the effect of the laser field, nor even simply the net effect of the electrons, we must also describe the complex interactions between the many electrons. In order to facilitate this description in a computationally tractable way we have developed time-dependent R-matrix theory (TDRM), and associated computer codes. The theory makes use of an R-matrix division of configuration space in order to simplify the calculations without neglecting important multielectron effects. It is our intention to extend the TDRM technique to describe relativistic effects in ultrafast processes. The spin-orbit interaction, wherein an electron's intrinsic (spin) and orbital angular momenta interfere to change its behaviour, gives rise to fine structure splittings in atomic energy levels. The transitions of electrons between these levels occurs on a time-scale governed by the energy gap. For heavier elements such as krypton and xenon this time-scale is of the order of a few femtoseconds- and so dynamics can evolve within a laser pulse. By opening up new electron-emission channels, and changing the selection rules for electron transitions, the spin-orbit effect can significantly alter the fundamental processes of attosecond physics- ionisation, harmonic generation etc. Hence, interesting new dynamics can be observed on the atomic scale. By using the TDRM method we will be able to model these dynamics from first principles, thus giving an unparallelled insight into some of the most fundamental physical processes in atomic science.