The DiPOLE Laser on the Helmholtz Beamline at XFEL

X射线是一种电磁辐射，其波长比固体中原子之间的距离短，因此它们可以用来“观察”原子尺度上的物质。在过去的几年里，X射线科学发生了一场革命：现在可以产生超短脉冲的激光X射线，持续时间不到十分之一万亿分之一秒，这也是原子在固体中来回振动所需的时间。因此，这种超亮的X射线激光使我们能够在没有运动模糊的情况下制作物质的频闪“电影”。第一台X射线激光器是在美国的斯坦福大学制造的，使用的是一台有50年历史的加速器。欧洲版本正在汉堡建造，正在从头开始建造，因此基于新颖的超导磁体技术，这意味着它将以比美国系统快100倍的速度产生X射线脉冲-这是技术的又一次飞跃。这里的建议是一个由10所领先大学组成的英国财团的设备请求，以帮助建立欧洲X射线自由电子激光（XFEL）的诊断终端站之一。该设备是一个非常强的光学激光器，与XFEL一起使用，允许物质首先被强光束照射，然后用独特的X射线束探测。这种光学/X射线组合将允许进行各种不同类型的研究。例如，当用强可见光照射样品时，表面被加热到等离子体形成的高温。等离子体膨胀到真空中（实验都是在没有空气的情况下进行的），反作用力将目标的其余部分压缩到高压-比木星中心的压力更大。在靶福尔斯分离之前，这些条件存在约十亿分之一秒，但在这短时间内，XFEL（与光学激光精确同步）从靶中的原子散射，记录的信号显示了它们的排列。通过这种方式，我们可以发现在我们自己的太阳系中巨行星中心发生的情况，并开始探索已发现的众多系外行星（现在已确认接近1000颗）内部可能存在的物质类型。这种光学/X射线激光的组合使得许多其他类型的实验成为可能-例如X射线激光本身可以将固体加热到几百万度（清醒地认识到，这些条件-比如每立方厘米1克，200万度，正是预测存在于太阳中心的一半）。此外，光学激光器可以与其他激光器配置以产生非常强烈的光-如此强烈，以至于光的电场中的电子被加速到如此高的速度，以至于它们的质量被爱因斯坦的相对论方程改变。当电子被来回甩时，它们会经历巨大的加速度，并且已经预测，由XFEL产生的X射线散射将允许在实验室中探索量子引力模型。这些高功率激光器也可以用来加速粒子（电子或质子）到非常高的能量，使紧凑的加速器-但所涉及的一些机制还没有完全理解-主要是因为我们不能“看到”粒子产生的目标内部。X射线激光将允许对目标进行这种探测，因此目标是制造更好的紧凑型加速器，可用于基础研究或医学应用，如治疗癌症。因此，可以看出，这种XEL机器与这里要求的光学激光器相结合的实验范围非常广泛，涉及英国科学家具有相当领导力和专业知识的学科范围。

X-rays are a form of electromagnetic radiation with wavelengths shorter than the distance between atoms in a solid, thus they can be used to 'view' matter on atomic dimensions. Over the past few years there has been a revolution in x-ray science: ultra-short pulses of laser-like x-rays can now be produced durations less than a tenth of a trillionth of a second, which is also the sort of time it takes for atoms to move back and forth as they vibrate within a solid. This ultra-bright X-ray laser thus allows us to make stroboscopic 'movies' of matter without motional blurring. The first x-ray laser to be built was in the US, at Stanford, using a 50-year old accelerator. The European version, under construction in Hamburg, is being built from scratch, and as such is based on novel superconducting magnet technology that means it will produce x-ray pulses at a rate several 100 times faster than that of the US system - producing another leap forward in technology. The proposal here is a request for equipment for a UK consortium of 10 leading Universities to help build one of the diagnostic end-stations on this European X-ray Free-Electron Laser (XFEL). The equipment is a very intense optical laser to go alongside the XFEL , allowing matter to first be irradiated by the intense optical beam, and then probed with the unique x-ray beam. This optical/x-ray combination will allow a whole range of different types of research to be performed. For example, when a sample is irradiated with intense optical light, the surface is heated to such high temperatures that a plasma forms. This plasma expands into the vacuum (the experiments are all performed without air), and the reaction force compresses the rest of the target to high pressures - greater than those found at the centre of Jupiter. These conditions exist for about a billionth of a second, before the target falls apart, but in that short time the XFEL (accurately synchronized to the optical laser) scatters from the atoms in the target, and the recorded signal shows their arrangement. In this way, we can discover the conditions that occur at the centre of the giant planets in our own solar system, and also start to explore the types of material that may exist inside the numerous exoplanets that have been discovered (now close to 1000 have been confirmed). This optical/x-ray laser combination makes possible many other types of experiments - for example the x-ray laser itself can heat a solid to several million degrees (it is sobering to realize that these sort of conditions - say a gram per centimeter cubed, and 2 million degrees, are exactly those predicted to exist half way to the centre of the sun). Furthermore, the optical laser can be configured with other lasers to produce very intense light - so intense that electrons within the electric field of the light are accelerated themselves to such high velocities that their mass is altered by Einstein's relativistic equations. As the electrons are flung back and forth, they experience huge accelerations, and it has been predicted that x-rays scattering from them, produced by the XFEL, will allow models of quantum gravity to be explored in the laboratory. These high power lasers can also be used to accelerate particles (electrons or protons) to very high energies, making compact acclerators - but some of the mechanisms involved are not fully understood - mainly because we cannot 'see' inside the target where the particles are produced. The X-ray laser will allow such probing of the target, and thus the aim is to make better compact accelerators that could be used either for fundamental research, or in medical applications, such as the treatment of cancer. It can thus be seen that the experiments that this XEL machine, in combination with the optical laser requested here, is very wide ranging, with implications across a spectrum of disciplines where UK scientists have considerable leadership and expertise.