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的纳米粒子的相互作用。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，其中热电子的子集被驱动通过与激光同相的颗粒，其中共振对颗粒尺寸非常敏感，以及（2）多个相位强激光束对控制强激光加热纳米颗粒的爆炸/膨胀的影响。对于较小的纳米粒子，强有质动力引起的变形和压缩预测的流体和粒子在细胞（PIC）模型。对于较大的粒子（大于50纳米）和数百飞秒的较长脉冲，烧蚀压缩似乎起作用。这些效应发生在一个独特的制度，近场限制，其中激光波长远大于集群的大小。诸如瑞利-泰勒不稳定性之类的问题不会出现，并且这些影响可能对具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定向和相位的强激光脉冲来控制。要做这些实验，以前的方法在几个方面受到限制。 首先，颗粒尺寸依赖的影响很可能被气体射流产生的货车德瓦耳斯团簇的宽尺寸分布完全掩盖。其次，喷流中的高簇密度限制了结果的总体平均值。光束撇除器和几何形状可以用来限制团簇密度，但团簇尺寸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的纳米颗粒，允许与预定固定尺寸的单个颗粒的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.