Coherent control of quantum systems with designer light fields

今天，我们对激光产生的光场有着难以置信的控制，无论是在时间上还是在空间上。我们可以控制激光脉冲的颜色、偏振和持续时间。我们可以结合几乎任意的频率和脉冲持续时间。我们可以控制激光束内光的空间特性。例如，我们可以创建中间有孔的光束，具有空间变化偏振矢量的光束，或者波前看起来像空间中的开瓶器的光束。对激光场的这种程度的控制开辟了新的应用，其中一些我将探讨。虽然圆偏振激光场是手性的，但它们的波长通常比单个分子大得多，也就是说，远离共振的分子只经历均匀的电场。我建议实现一个激光场，在空间的每一点都是手性的，这将允许比通常使用的方法，如光电子圆二色性，更有效地区分左手和右手分子。我将使用重合光电子光离子动量谱，即COLTRIMS或反应显微镜，来检测电离产率、光电子分子框架角分布和库仑爆炸成像中的手性相关信号。除了开发一种新的结构诊断工具外，我还建议对水中的超快弛豫过程进行激发和成像。水二聚体作为最接近液态水的物质，可以作为理解高能光子引发的过程的试验场。尽管软x射线在不同领域具有重要意义，但人们对其在水中的吸收了解甚少。了解水中x射线光子吸收的能量和电荷再分配对于设计更有效的放射肿瘤学方案，解开对活组织遗传毒性作用的物理基础以及在x射线衍射实验中最大限度地减少生物样品的损伤至关重要。这两个项目都提供了充分的扩展和未来研究的机会。

Today we have incredible control over the optical fields created by lasers, both in time and in space. We can control the color, polarization and duration of laser pulses. We can combine nearly arbitrary frequencies and pulse durations. We can control the spatial properties of the light within the laser beam. For example we can create beams with a hole in the middle, beams with a spatially varying polarization vector, or beams whose wave front looks like a corkscrew in space. This degree of control over laser fields opens up new applications, some of which I will explore. While circularly polarized laser fields are chiral their wavelength is generally much larger than a single molecule, i.e., away from resonances a molecule experiences only a homogeneous electric field. I propose to realize a laser field that is chiral at every point in space and that will permit to distinguish left and right-handed molecules much more efficiently than commonly used methods such as photoelectron circular dichroism. I will use coincidence photoelectron photoion momentum spectroscopy, known as COLTRIMS or reaction microscopy, to detect a chirality dependent signal in ionization yields, photoelectron molecular frame angular distribution and Coulomb explosion imaging. In addition to developing a new structural diagnostic tool, I propose to excite and image ultrafast relaxation processes in water. Water dimers as the simplest approximation to liquid water can serve as testing ground to understand the processes that are initiated by high energy photons. Soft X-ray absorption in water is understood poorly despite its paramount importance in different fields. Understanding the energy and charge redistribution on X-ray photon absorption in water is vital for the design of more-efficient radiooncology schemes, for disentangling the physical basis of genotoxic effects on living tissues and for minimizing the damage of biological samples during X-ray diffraction experiments. Both projects provide ample opportunity for expansion and future research.