Particle Acceleration with High Intensity Mid-IR Lasers.

一个聚焦良好的高功率（多太瓦）激光脉冲能够在10E19 Wcm^-2以上的目标上传递强度，并在几飞秒的时间尺度上驱动和探测外来过程。在这些极端条件下，可以产生和利用比经典RF加速器结构中所能达到的大得多的大电场。像电子这样的带电粒子可以在一个光周期内被加速到相对论强度（质量变化变得显著）。当强光脉冲在物质中传播时，也可以产生等离子体“气泡”结构，这可以在几厘米的长度尺度上捕获和加速电子到多gev的能量。迄今为止，大多数激光加速实验都是使用大型“国家设施”规模的激光器进行的，工作在1um或800nm。然而，在所谓的中红外光谱范围内，有令人信服的理由转向波长更长的激光器。随着波长越长，光周期时间越长，电子会受到更大的加速力，其大小为波长的平方。因此，在同等能量和强度下，4um的激光可以驱动粒子达到16倍的能量。对于气泡状态加速器来说，由于需要将激光脉冲与等离子体中的色散等条件相匹配，情况变得更加复杂，而在这种情况下，波长较长的激光似乎也有一些优势。然而，目前还没有高功率（bbb1tw）商用MIR激光系统，而且由于缺乏“经典”增益存储材料，无法在该波长范围内以必要的带宽放大低于100fs的脉冲，因此构建这样一个系统是一个重大的技术挑战。该项目将以帝国理工学院正在建造的奇美拉多波长MIR激光器为基础。学生将努力优化这个复杂的光参数啁啾脉冲放大系统的性能，使其能够驱动和探测高能量密度的物理实验。博士项目将包括通过测量和控制高阶相位来优化激光脉冲压缩，并将激光能量扩大到100兆焦耳水平。该学生将模拟、构建、运行和分析激光驱动粒子加速实验的数据，使用奇美拉激光器和场外设施，如卢瑟福阿普尔顿实验室的双子座激光器。

A well focused high-power (multi-terrwatt) laser pulse is able to deliver intensities on target above 10E19 Wcm^-2 and drive and probe exotic processes on a few femtosecond timescale. Under these extreme conditions, large electric fields, significantly greater than those attainable in a classic RF accelerator structure can be created and exploited. Charged particles such as electrons can be accelerated to relativistic intensities (where mass change becomes significant) over a single optical cycle. It is also possible to create plasma "bubble" structures as an intense light pulse propagates through matter, and this can trap and accelerate electrons to multi-GeV energies over length scales of a few cm.To date, most laser acceleration experiments have been undertaken using large "National Facility" scale lasers operating at 1um or 800nm. However there are compelling reasons to move to longer wavelength lasers in the so-called Mid-IR spectral range. As the optical cycle time increases for longer wavelengths, electrons experience a greater accelerating force, which scales as wavelength squared. Thus a 4um laser can potentially drive a particle to ~16x higher energies than a 1um laser of equivalent energy and intensity. For a bubble regime accelerator, the situation is further complicated by the need to match a laser pulse to conditions such as dispersion in a plasma, and here longer wavelengths also appear to have some advantages. However there are no high-power (>1TW) commercial MIR laser systems available, and building such a system is a significant technical challenge as there is a lack of "classic" gain storage materials able to operate in this wavelength range with the necessary bandwidth to amplify a sub 100fs pulse.This project will build on the Chimera multi-wavelength MIR laser being constructed at Imperial College. The student will work to optimise the performance of this complex optical parametric chirped pulse amplification system to enable it to drive and probe high energy density physics experiments. The PhD project will include optimisation of laser pulse compression by measurement and control of high-order phase, and scale up of laser energy to the >100mJ level. The student will model, construct and run and analyse data from laser driven particle acceleration experiments using both the Chimera laser and off site facilities such as the Gemini laser based at the Rutherford Appleton Laboratory.