Particle Acceleration with High Intensity Mid-IR Lasers.

一个聚焦良好的高功率（数瓦）激光脉冲能够在靶上产生10 E19 Wcm^-2以上的强度，并在几个飞秒时间尺度上驱动和探测奇异过程。在这些极端条件下，可以产生和利用比经典RF加速器结构中可达到的电场大得多的大电场。带电粒子如电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）。它也可以创建等离子体“气泡”结构作为一个强烈的光脉冲传播通过物质，这可以捕获和加速电子到多GeV的能量超过几厘米的长度尺度。迄今为止，大多数激光加速实验已经进行了使用大型“国家设施”规模的激光器在1微米或800纳米。然而，有令人信服的理由在所谓的中红外光谱范围内转向更长波长的激光器。随着波长变长，光周期时间增加，电子会受到更大的加速力，加速力与波长的平方成正比。因此，4um激光器可以潜在地驱动粒子到比同等能量和强度的1um激光器高约16倍的能量。对于气泡状态加速器，由于需要将激光脉冲与等离子体中的色散等条件相匹配，情况进一步复杂化，并且这里较长的波长似乎也具有一些优势。然而，目前还没有高功率（> 1 TW）的商用MIR激光系统，而建造这样一个系统是一个重大的技术挑战，因为缺乏能够在这个波长范围内工作的“经典”增益存储材料，其带宽足以放大100 fs以下的脉冲。学生将致力于优化这种复杂的光学参量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，并将激光能量放大到> 100 mJ的水平。学生将建模，构建，运行和分析来自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，如位于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.