X-ray probing of controlled photo-induced dynamics

物质光致动力学的量子控制是一个具有科学挑战性和技术意义的重要课题。鉴于锥形交叉点（多维电位表面交叉点）在光化学中所起的关键作用，考虑通过锥形交叉点引导进化分子系统的量子路径的可能性是特别有趣的。这可以通过制备电子态的相干叠加并在交叉过程中控制这种叠加的演变来实现。考虑到动力学的超快性质通常与锥形交叉的交叉和准备电子态叠加所需的大相干带宽有关，这本身需要非常短（几飞秒）的光脉冲，我们必须在极短的时间尺度上运行激光场来实现这一点。此外，我们还需要一种具有足够时间分辨率和电子状态特异性的探测方法来跟踪和确认动力学及其控制。该项目将使用我们基于高谐波产生的x射线方法-显示能够产生从100 eV到600 eV的亚飞秒x射线脉冲来探测气相光化学反应-通过时间分辨近边缘光谱在C和N K边缘探测动力学。这种光化学反应将反过来通过使用非线性光学方法产生的深紫外脉冲（例如光子晶体光纤产生色散波）触发，并使用与泵和探头同步产生的几个周期激光脉冲来控制。这项工作将开创在极端时间尺度下探测物质动力学所需的超快激光技术的新技术。

The quantum control of photo-induced dynamics in matter is a scientifically challenging and technology important objective. Given the key role conical intersections (multi-dimensional potential surface crossings) are now believed to play in photochemistry it is especially intriguing to consider the possibility to steer the quantum path of an evolving molecular system across a conical intersection. This may be done by preparing a coherent superposition of electronic states and steering the evolution of this superposition during the crossing. Given the ultrafast nature of the dynamics normally associated with the crossing of a conical intersection and the large coherent bandwidth required to prepare an electronic state superposition, which itself requires a very short (few femtosecond) light pulse we must have laser fields operating at extremely short timescales to achieve this. Further we require a probing method with sufficient time resolution and electronic state specificity to track and confirm the dynamics and their control.The project will use our high harmonic generation based X-ray method - shown to be capable of generating sub-femtosecond X-ray pulses from 100 eV to 600 eV to probe gas phase photochemical reactions- to probe the dynamics through time resolved near edge spectroscopy at C and N K edges. This photochemistry will in turn be triggered via deep UV pulses generated using non-linear optical methods (e.g. photonic crystal fibre generate dispersive waves) and controlled using a few-cycle laser pulses synchronously generated with the pump and probe. The work will pioneer new techniques in the ultrafast laser technology required for probing dynamics in matter at extreme timescales.