Pump laser for TW laser system

约翰·亚当斯研究所(JAI)是先进加速器科学和技术的卓越中心，总部设在牛津大学、伦敦皇家霍洛威大学和伦敦帝国理工学院。Jai研究的一个重要主题是开发先进的等离子体加速器。它们利用由强激光脉冲(或粒子束)驱动的密度波在等离子体中传播时产生的巨大电场。激光驱动的等离子体加速器产生的电子束的能量相当于在等离子体加速器阶段将它们加速到近100亿伏特所获得的能量，而等离子体加速器阶段只有几厘米长。因此，等离子体加速器有可能驱动致密的高能粒子源，通过磁场振荡这些粒子--就像今天体育场大小的同步加速器设施中所做的那样--它们可以产生非常明亮的X射线源，用于科学、医学和工业。从长远来看，等离子体加速器可以用于新一代高能粒子对撞机。激光尾波场加速器(LWFA)的JAI计划旨在解决许多关键问题，这些问题需要在实现其许多有前途的应用之前得到解决。在牛津，这项工作集中在开发一种架构，使高能等离子体加速器能够以高(千赫)重复频率运行。该体系结构的第一个组件是牛津大学开发的流体动力学光场电离(HOFI)等离子体通道。这是一种独立的、“坚不可摧”的光波导，能够在米级距离内传输相对较强的激光脉冲。因此，它们是未来高重复频率激光等离子体加速器中提供等离子体“靶标”的关键技术。第二个组件是多脉冲LWFA(MP-LWFA)概念，也是在牛津大学开发的。这种新的方法试图克服LWFA应用中的一个基本障碍：今天使用的短脉冲(不到十亿分之一秒)、高能(几焦耳)的钛蓝宝石激光器的壁塞效率非常低(&lt；0.1%)，并且仅限于以每秒几个脉冲的重复频率运行。相比之下，LWFA的许多短期或中期应用需要每秒传输数千个脉冲；而长期应用，如粒子对撞机，也需要更高的壁塞效率。MP-LWFA的基本思想是用一系列低能量激光脉冲而不是单个高能脉冲来驱动等离子体波。列车中的每个脉冲激发一个低幅度的等离子体波，如果脉冲与等离子体波的波长隔开，则等离子体波相干地相加，导致等离子体波的幅度朝着列车的后部增长。这一新方法为LWFA开辟了新的、高效的激光技术，这些技术不能直接产生短脉冲，但可以在高(千赫)重复频率下提供更长、高能量的脉冲。目前的提案包括申请资金以更换泵浦激光器，泵浦激光器是在JAI等离子体加速器研究方案中广泛使用的太瓦激光系统的核心。这台泵浦激光器已经有近20年的历史了，制造商将不再对其进行维护或维修。如果它失败了，我们就无法完成我们的研究计划的很大一部分。

The John Adams Institute (JAI) is a centre of excellence for advanced accelerator science and technology, based at the University of Oxford, Royal Holloway University of London, and Imperial College London. An important theme within JAI's research is the development of advanced plasma accelerators. These exploit the huge electric fields developed within density waves driven by intense laser pulses (or particle bunches) as they propagate through plasma. Laser-driven plasma accelerators have generated electron bunches with energies equivalent to that obtained by accelerating them across nearly 10 billion volts in plasma accelerator stages only a few centimetres long. Plasma accelerators therefore offer the potential to drive compact sources of energetic particles, and by oscillating these particles with magnetic fields -- as is done in today's, stadium-sized synchrotron facilities -- they could generate very bright X-ray sources for use in science, medicine, and industry. In the longer term, plasma accelerators could be used in a new generation of high energy particle colliders.The JAI programme on Laser Wakefield Accelerators (LWFAs) aims to tackle many of the key issues which need to be solved before their many promising applications can be realized. In Oxford, this work concentrates on developing an architecture for enabling high-energy plasma accelerators operating at high (kilohertz) repetition rates. The first component of this architecture is the hydrodynamic optically-field-ionized (HOFI) plasma channel, which was developed at Oxford. These are free-standing, "indestructible" optical waveguides capable of channelling relativistically-intense laser pulses over metre-scale distances. As such, they are a key technology for providing the plasma "target" in future high-repetition-rate laser-plasma accelerators.The second component is the multi-pulse LWFA (MP-LWFA) concept, also developed in Oxford. This new approach seeks to overcome a fundamental road-block in the application of LWFAs: the short pulse (less than one-ten-billionth of a second), high-energy (a few joules) Ti:sapphire lasers used today have very low wall-plug efficiency (< 0.1%), and are limited to operation at repetition rates of only a few pulses per second. In contrast, many near- or medium-term applications of LWFAs require the delivery of thousands of pulses per second; and longer-term applications, such as particle colliders, also require much higher wall-plug efficiency.The essential idea of MP-LWFA is to drive the plasma wave with a train of low energy laser pulses, rather than with a single, high-energy pulse. Each pulse in the train excites a low amplitude plasma wave, and if the pulses are spaced by the wavelength of the plasma wave, then the plasma waves add coherently, causing the amplitude of the plasma wave to grow towards the back of the train. This new approach opens up LWFAs to novel, efficient laser technologies which cannot generate short pulses directly, but which can provide longer, high-energy pulses at high (kilohertz) repetition rates. The current proposal comprises a request funds to replace a pump laser which lies at the heart of the terawatt laser system used extensively in the JAI plasma accelerator research programme. This pump laser is nearly 20 years old and the manufacturer will no longer service or repair it. If it were to fail we could not complete a large fraction of our research programme.