Contrast enhancement and advanced laser pulse diagnosis techniques

这次学习活动将在帝国理工学院等离子体物理系内举行。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体进行，在项目过程中开发的新仪器将可用于AWE的现场测试。该项目将研究皮秒时间尺度上时间对比度退化的机制。当使用参数放大过程时，可能的候选包括来自脉冲展宽器中的衍射栅的非相干散射以及泵浦脉冲时间轮廓上的幅度噪声。这项工作也与Imperial主持的其他主要项目很好地结合在一起，包括由DSTL和US AFOSR资助的开发新的中红外高功率激光源的工作，提供了一个独特的环境来研究对比度退化过程的波长缩放。该项目还将解决与使用大口径光束的啁啾脉冲放大相关的问题，在这种情况下，不完美的波前质量和过程，如色差，可能会导致脉冲压缩器孔径上的时间强度轮廓扭曲。即使在光束的波前名义上是平坦的情况下也是如此。这种波前失真的问题导致远场(焦点，大多数物理实验进行的点)相对于测量的脉冲持续时间的时间展宽。通常，脉冲持续时间测量是利用近场中的光束孔径的子样本进行的。在此样本中，脉冲可以局部较短，但全局较长。出于这个原因，该项目将致力于开发能够在大口径下表征这一现象的仪器。

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.