Ultrafast structural dynamics by crystallography and coherent control

van Thor小组专门研究光敏蛋白的超快结构动力学，阐明关键生物反应中的核和电子动力学。第四代光源x射线自由电子激光器（XFELS）的出现，为泵浦探测光谱提供了前所未有的埃波长时间分辨率。该小组在利用这些仪器开发新的实验超快技术方面处于领先地位，特别是时间分辨串行飞秒晶体学（TR-SFX）和相应的理论本博士项目的目标是在此基础上进行理论支持的实验，以阐明结构动力学的相干控制。众所周知，在生物蛋白的光激发后，在基态和激发态都会产生较大的振动相干性抑制或增强一致性可以导致对状态和反应途径中的群体的操纵。光控制是一种通过改变激光脉冲的特性来控制基态和激发态相干振幅的方法。脉冲的峰值功率、脉冲持续时间、载波频率和二阶色散都对相干幅值有影响此外，最近已经观察到二次（倾倒）脉冲可以增强基态的相干性。该项目的初始工作将是与海德堡巴克普小组合作开发理论模拟，以补充历史上的XFEL晶体学实验。这些模拟结果将为未来的实验结果提供理论支持，并影响实验设计。模拟采用非微扰时间相关密度矩阵模型，并监测了外电场（激光脉冲）扰动后的瞬态效应模拟将允许对多个激光脉冲的特性进行完全控制，从而可以研究上述光学控制的所有方面。相干分析可以通过将密度矩阵转换为半经典维格纳相空间表示来识别，并分辨出相干振幅。在模拟完成后，工作将开始开发设备，以允许脉冲整形在家庭激光实验室中操纵脉冲特性。采用超快瞬态吸收光谱技术，结合主动脉冲整形，将允许脉冲拉曼光谱对分子动力学进行相干控制。此外，优化脉冲特性的相干控制，然后可以在TR-SFX实验中实现光束时间在XFELs。除了光学控制外，相干性还可以通过蛋白质晶体的结构、对称性和方向性来控制。二维电子光谱和红外光谱已经被确定为一种可以识别这些性质对振动相干性的影响的技术。本项目希望通过相干控制来阐明结构动力学，将多种实验技术与理论相结合。研究光学和结构上相干控制的多个方面。

The van Thor group specialises in the investigating ultrafast structural dynamics of light-sensitive proteins,elucidating the nuclear and electronic dynamics in key biological reactions. The advent of fourth-generationlight sources, X-ray free electron lasers (XFELS), has allowed unprecedented temporal resolution ofangstrom wavelength for pump-probe spectroscopy. The group is at the forefront of utilising theseinstruments in developing novel experimental ultrafast techniques, specifically time-resolved serialfemtosecond crystallography (TR-SFX) and the corresponding theory.1,2 The objective of this PhD projectis to build upon this work and conduct experiments supported by theory to elucidate structural dynamics bycoherent control.It is known that large vibrational coherence is generated in both the ground and excited states, followingoptical excitation of biological proteins.1 Suppressing or enhancing coherence, can lead to manipulation ofthe populations in states and reaction pathways. Optical control is a method whereby changing thecharacteristics of the laser pulses can manipulate the coherent amplitude in both ground and excited states.The peak power, pulse duration, carrier frequency and second-order dispersion of a pump pulse have allbeen shown to impact coherent amplitude.2,3 Additionally, it has been recently observed that secondary(dump) pulses can enhance coherence in the ground state.The initial work of this project will be to develop theoretical simulations in collaboration with the Buckupgroup Heidelberg, to compliment historic XFEL crystallographic experimentation. The simulations will thenbe used to provide theoretical support for future experimental results and influence experimental design.The simulations employ a non-perturbative time-dependant density matrix model and monitors the transienteffect after perturbation from an external electric field (laser pulse).4 The simulations will allow full controlof the characterisation of multiple laser pulses, such that all facets of optical control described above canbe investigated. Analysis of the coherence can be discerned by a transformation of the density matrix tothe semi-classical Wigner phase space representation and coherent amplitudes resolved.5Upon completion of the simulations, work will begin on developing the apparatus to allow pulse shaping tomanipulate the pulse characteristics in the home laser laboratory. Employing ultrafast transient absorptionspectroscopy technique, combined with active pulse shaping will allow coherent control of moleculardynamics by impulsive Raman spectroscopy. Furthermore, the optimisation of pulse characteristics forcoherent control can then be implemented in TR-SFX experiments with beam times at XFELs.In addition to optical control, coherence can be controlled via the structural, symmetry and directionalproperties of protein crystals. Two dimensional electronic and infrared spectroscopy has been identified astechniques which could discern the effects these properties have on vibrational coherence.6This project hopes to elucidate structural dynamics by coherent control, incorporating multiple experimentaltechniques with theory. Investigating multiple facets of coherent control both optically and structurally.