Radiation pressure effects at the focus of intense lasers

最先进的激光现在可以达到远远超过1020WCM-2的聚焦强度。当定向到密度足以阻止激光的目标时，强烈的辐射压力可以直接驱动目标的临界密度面。这可以通过多种方式表现出来。它可以驱动一种无碰撞的冲击，这可以通过它在其路径上加速的离子来诊断。或者，对于足够薄的目标，整个等离子体可以向前推进，在传播时获得动量。这两种情况的结果都是产生密集的高能离子束。这些离子可能会有很多应用，尤其是在下一代粒子加速器中。这里提出的项目将通过优化目标和驱动它们的激光束的特性来研究辐射压力驱动加速方案。这些实验将在卢瑟福-阿普尔顿实验室的高强度激光和ATF布鲁克海文国家实验室的红外激光上进行。近期的目标是生产能量超过100 MeV的质子，这将对肿瘤的辐射治疗或聚变胶囊的快速加热等应用感兴趣。

State-of-the-art lasers can now reach intensities well in excess of 1020 Wcm-2 at focus. When directed onto a target that is sufficiently dense that it can stop the laser beam, the intense radiation pressure can directly drive the critical density surface of the target. This can manifest itself in a number of ways. It can drive a collisionless shocks which can be diagnosed by the ions it accelerates in its path. Alternatively, for sufficiently thin targets, the whole plasma can be propelled forward gaining momentum as it propagates. The result in both cases is the production of dense beams of energetic ions. These ions could have numerous applications, not least in next-generation particle accelerators. The project proposed here will investigate radiation pressure driven acceleration schemes through optimisation of targets and of the characteristics of the laser beam that drives them. The experiments will take place on the high intensity lasers at the Rutherford-Appleton Laboratory and the IR laser at the ATF Brookhaven National Laboratory. A near term goal is to produce protons with energies exceeding 100 MeV, which would be of interest for applications such as radiation treatment of tumours or for fast heating of fusion capsules.