Control of high energy density nanoplasmas with intense laser pulses

该项目的主要部分集中在强激光脉冲与单一尺寸选定纳米颗粒的相互作用。具体而言，实验将研究(1)纳米颗粒中的一种新型激光吸收共振，其中一组热电子与激光相驱动通过颗粒，其中共振对颗粒尺寸非常敏感；(2)多相强激光束对控制强激光加热纳米颗粒爆炸/膨胀的影响。对于较小的纳米颗粒，流体和颗粒-细胞（PIC）模型都预测了强质量动势引起的扭曲和压缩。对于更大的粒子（大于50纳米）和数百飞秒的更长的脉冲，烧蚀压缩似乎起了作用。这些效应发生在一个独特的区域，即近场极限，在这里激光波长比团簇大小大得多。诸如瑞利-泰勒不稳定性之类的问题不会进入图像，并且效果可能对带有热点的低质量激光束不敏感。有趣的可能性是，热致密物质在亚波长空间尺度上的动力学可以通过适当的定向和相位强激光脉冲来控制。为了进行这些实验，以前的方法在几个方面受到限制。首先，粒子大小相关的效应可能完全被气体喷射的范德华团簇的宽尺寸分布所掩盖。其次，射流中的高星团密度限制了结果的总体平均值。束掠光器和几何形状可以用来限制簇密度，但簇大小分布的问题仍然存在。所描述的方法将允许产生非常低密度的单一尺寸纳米颗粒，允许与预定固定尺寸的单个颗粒进行一致的激光相互作用。

The main part of this project concentrates on the interaction of intense laser pulses with single size selected nanoparticles. Specifically, experiments will investigate (1) a new type of laser absorption resonance in nanoparticles whereby a subset of hot electrons is driven through the particle in phase with the laser, where the resonance is strongly particle size-sensitive, and (2) the effects of multiple phased intense laser beams on controlling the explosion/expansion of intense laser-heated nanoparticles. For smaller nanoparticles, strong ponderomotive force-induced distortion and compression is predicted by both fluid and particle-in-cell (PIC) models. For larger particles (larger than 50 nanometers) and longer pulses in the hundreds of femtoseconds, ablative compression appears to play a role. These effects take place in a unique regime, the near field limit, where the laser wavelength is much larger than the cluster size. Issues such as the Rayleigh-Taylor instability do not enter the picture and the effects may be insensitive to low quality laser beams with hot spots. The intriguing possibility is that the dynamics of hot dense matter on a sub-wavelength spatial scale could be controlled with appropriately directed and phased intense laser pulses. To do these experiments, previous methods are limited in several ways. First, particle size-dependent effects are likely to be completely masked by the wide size distribution of van der Waals clusters from gas jets. Second, the high cluster density in jets limits results to ensemble averages. Beam skimmers and geometry can be used to limit the cluster density, but the problem of the cluster size distribution remains. The methods described will allow the generation of very low densities of single-size nanoparticles, allowing consistent laser interactions with single particles of predetermined fixed size.