Focusing Plasma Optics: Towards Extreme Laser Intensities

光学聚焦光的使用可以追溯到古埃及人，并且在几个世纪以来为许多科学发现和创新做出了贡献。近年来，使用光学聚焦激光束已经产生了无数的应用，不仅在科学，而且在信息技术，医学，工业，消费电子，娱乐和国防。随着越来越高的聚焦激光强度的实现，强激光在原子和分子物理学以及等离子体物理学中发挥了革命性的作用。在今天可以达到的最高强度下，聚焦激光通过产生极端压力、温度和强烈的电场和磁场，包括驱动具有独特性质的高能粒子和辐射源，正在开辟科学的新领域。几个世纪以来，基于使用固态光学介质的传统聚焦光的方法并没有从根本上改变，但正迅速成为超强激光科学进一步发展的关键限制因素。造成这种情况的主要原因是固态光学介质在损坏之前所能承受的能量密度是有限的。传统的规避方法是随着激光能量的增加而增加聚焦光学的尺寸，使总能量密度低于临界值。然而，用于最高功率激光器（如英国中央激光设施的Vulcan千瓦激光器）的光学元件现在直径超过一米，而且非常昂贵，由于它们的体积和重量，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，以及为了生产用于应用的紧凑型高强度激光驱动器，需要彻底的新方法。本课题旨在探索基于超快等离子体过程的新型聚焦光学系统-聚焦等离子体光学-的开发和应用的可行性，以扩展高功率激光脉冲可实现的强度边界。由于等离子体光学元件能够承受极大振幅的电磁场，因此它们具有固有的紧凑性。能量密度比传统的固态光学器件要高100倍以上，这意味着等离子体光学器件要小10倍以上。此外，激光激发等离子体的光学特性的超快演变使得激光脉冲的其他特性可以被定制。由于这些原因，等离子体光学元件很可能成为未来高功率激光设备的基本元件。提出的工作包括探索实现等离子体聚焦的两种途径-由于弯曲等离子体表面的反射而聚焦和由于透明等离子体中的非线性等离子体效应而自诱导聚焦。介绍了控制所获得的焦点光斑特性的创新方法。这将使目前可达到的最大强度增加大约10到20倍，开启了在极高温度和压力条件下探索物质的大门。它还将支持紧凑型激光驱动高能粒子和辐射源的应用发展。因此，本项目所研究的聚焦等离子体光学作为下一代光学器件具有真正革命性的潜力。

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.