Contrast enhancement and advanced laser pulse diagnosis techniques

该奖学金将在帝国理工学院的等离子体物理组内举办。大部分实验工作将在罗兰A史密斯教授的监督下在布莱克特实验室激光联合会进行，在项目过程中开发的新仪器将在AWE现场进行测试。该项目将研究皮秒时间尺度上时间对比度退化的机制。潜在的候选者包括来自脉冲展宽器中的衍射光栅的非相干散射和当使用参量放大过程时泵浦脉冲的时间轮廓上的幅度噪声。这项工作也与帝国理工主持的其他主要项目保持一致，包括由DSTL和美国AFOSR资助的开发新的中红外高功率激光源的工作，该项目还将解决与啁啾脉冲放大相关的问题，使用大孔径光束，不完美的波前质量和过程，如色差可能导致脉冲压缩器孔径上的时间强度分布的失真。即使在光束的波前名义上是平坦的情况下，这也是真实的。波前畸变的这个问题导致相对于测量的脉冲持续时间在远场（在焦点处，进行大多数物理实验的点）中的时间加宽。通常，脉冲持续时间测量是用近场中的射束孔径的子样本进行的。脉冲在该样本内可以是局部短的，但是全局较长。出于这个原因，该项目将致力于开发能够在大孔径下实现这一点的仪器。

This studentship will be hosted within the Plasma Physics group at Imperial College. The majority of the experimental work will take place in the Blackett Laboratory Laser Consortium under the supervision of Prof. Roland A Smith and new instruments developed over the course of the project will be made available for testing on site at AWE. The project will investigate mechanisms for the degradation of temporal contrast on picosecond timescales. Potential candidates include incoherent scattering from diffraction gratings in the pulse stretcher and amplitude noise on the temporal profile of the pump pulse when using parametric amplification processes. This work is also well aligned to other major projects hosted by Imperial, including work funded by DSTL and the US AFOSR to develop new mid-IR high power laser sources, providing a unique environment in which to investigate wavelength scaling of contrast degradation processes.The project will also address issues associated with Chirped Pulse Amplification using large aperture beams where imperfect wavefront quality and processes such as chromatic aberration can lead to distortion of the temporal intensity profile across the aperture of a pulse compressor. This can be true even where the wavefront of the beam is nominally flat. This problem of wavefront distortion leads to temporal broadening in the far-field (at focus, the point where most physics experiments are conducted) relative to the measured pulse duration. Typically pulse duration measurements are made with a sub-sample of the beam aperture in the near-field. The pulse can be locally short within this sample, but globally longer. For this reason the project will aim to develop instruments that can characterise this at large aperture.