Armoured: Atomic R-matrix Method For Relativistic Dynamics

为了“观察”原子中的电子，我们需要能够描述它们在与相互作用本身相当的时间尺度上的运动。这类似于拍照--物体移动得越快，拍摄它所需的曝光时间就越短。谐波产生的过程--原子中的电子在激光场的驱动下，重新发出激光的高次谐波--为探测原子和分子结构提供了一种独特的工具--可以成像分子轨道，甚至可以拍摄发生化学反应的视频。虽然这个阿秒物理领域(1阿秒=十亿分之一秒)已经建立得很好，但对潜在过程的理论描述和计算模型还不够发达。为了全面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影响，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的复杂相互作用。为了以易于计算的方式促进这种描述，我们已经开发了依赖时间的R-矩阵理论(TDRM)和相关的计算机代码。该理论利用了组态空间的R矩阵划分，以便在不忽略重要的多电子效应的情况下简化计算。我们打算将TDRM技术扩展到描述超快过程中的相对论效应。在自旋-轨道相互作用中，电子的本征(自旋)动量和轨道角动量相互干扰以改变其行为，导致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由能隙控制的时间尺度上。对于更重的元素，如氪和氙气，这个时间尺度是几飞秒的量级--因此动力学可以在一个激光脉冲内演化。通过打开新的电子发射通道，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，可以在原子尺度上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洞察。

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.