Focusing Plasma Optics: Towards Extreme Laser Intensities

使用光学聚焦光线的历史可以追溯到古埃及人，几个世纪以来一直有助于许多科学发现和创新。近年来，使用光学聚焦激光束已经导致了无数的应用，不仅在科学领域，而且在信息技术、医学、工业、消费电子、娱乐和国防领域。随着越来越高的聚焦激光强度的实现，强激光首先在原子和分子物理学，然后在等离子体物理学中发挥了革命性的作用。在当今可达到的最高强度下，聚焦激光通过产生极端压力、温度和强电场和磁场，包括驱动具有独特性质的高能粒子和辐射源，正在开辟科学的新前沿。基于使用固态光学介质的传统聚焦光方法，几个世纪以来没有根本改变，但正迅速成为进一步发展超强激光科学的关键限制因素。其主要原因是固态光学介质在其被损坏之前能够承受的能量密度存在限制。传统的规避方法是随着激光能量的增加而增加聚焦光学器件的尺寸，使得总能量密度低于临界值。然而，用于最高功率激光器（例如英国中央激光设施的Vulcan petawatt激光器）的光学器件现在直径超过一米，并且非常昂贵，由于其体积和重量，制造时间长，机动性有限。为了使最大可实现的激光强度继续增加，并为生产紧凑的高强度激光驱动器的应用，需要激进的新方法。本提案旨在探索开发和应用基于超快等离子体工艺的新型聚焦光学系统的可行性-聚焦等离子体光学-以扩展高功率激光脉冲可实现的强度前沿。由于等离子体光学部件能够维持极大振幅的电磁场，因此等离子体光学部件固有地紧凑。比传统固态光学器件高出一百倍以上的能量密度是容易实现的，这意味着等离子体光学器件小了十倍以上。此外，激光激发等离子体的光学性质的超快演化使得能够定制激光脉冲的其他性质。基于这些原因，等离子体光学元件很可能成为未来高功率激光装置的基本元件。拟议的工作涉及探索两种途径实现等离子体聚焦-聚焦由于从弯曲的等离子体表面的反射和自诱导聚焦由于在透明等离子体中的非线性等离子体效应。介绍了控制焦斑特性的创新方法。这将使目前可实现的最大强度增加约10至20倍，从而开辟了在极高温度和压力条件下探索物质的途径。它也将支持小型激光驱动的高能粒子和辐射源的应用发展。因此，在这个项目中研究的聚焦等离子体光学器件作为下一代光学器件具有真正的革命性潜力。

The use of optics to focus light dates back to the ancient Egyptians and has been instrumental over the centuries in contributing to many scientific discoveries and innovations. In recent years the use of optics to focus laser beams has resulted in countless applications, not only in science, but in information technology, medicine, industry, consumer electronics, entertainment and defence. As ever higher focused laser intensities have been achieved, intense laser light has played a revolutionary role, first in atomic and molecular physics and then plasma physics. At the highest intensities achievable today, focused laser light is opening up new frontiers in science via the production of extreme pressures, temperatures and intense electric and magnetic fields, including driving sources of high energy particles and radiation with unique properties.The conventional approach to focusing light, based on the use of solid state optical media, has not fundamentally changed over the centuries, but is rapidly becoming a key limiting factor for the further development of ultra-intense laser science. The main reason for this is that there is a limit to the energy density which solid state optical media can withstand before it is damaged. The traditional way to circumvent this is to increase the size of the focusing optic as the laser energy is increased, so that the overall energy density is below the critical value. However, the optics used on the highest power lasers (such as the Vulcan petawatt laser at the UK's Central Laser Facility) are now more than a meter in diameter and are very expensive, with long manufacture times and limited manoeuvrability due to their volume and weight. Radical new approaches are required to enable the maximum achievable laser intensity to continue to be increased and for the production of compact high intensity laser drivers for application.This proposal aims to explore the feasibility of developing and applying new types of focusing optical systems based on ultrafast plasma processes - focusing plasma optics - to extend the intensity frontier achievable with high power laser pulses. Due to their ability to sustain extremely large amplitude electromagnetic fields, plasma optical components are inherently compact. Energy densities of more than a factor of a hundred higher than conventional solid state optics are easily achievable, which means that plasma optics are more than a factor of ten smaller. Furthermore, the ultrafast evolution of the optical properties of laser-excited plasma enables other properties of the laser pulse to be tailored. For these reasons plasma optical components are likely to become essential elements of future high power laser facilities. The proposed work involves exploring two avenues for achieving plasma focusing - focusing due to reflection from a curved plasma surface and self-induced focusing due to non-linear plasma effects in transparent plasma. Innovative approaches to controlling the properties of the focal spot achieved are introduced. This will enable approximately a factor of 10 to 20 increase in the maximum intensities achievable at present, opening up the exploration of matter under extremely high temperature and pressure conditions. It will also underpin the development of compact laser-driven high energy particle and radiation sources towards application. Thus the focusing plasma optics to be investigated in this project have truly revolutionary potential as next generation optical devices.