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的选定纳米颗粒的相互作用上。具体地说，实验将研究(1)一种新型的纳米粒子中的激光吸收共振，其中热电子的子集被驱动通过与激光同相的粒子，其中该共振是强烈的颗粒尺寸敏感的，以及(2)多个相位强激光光束对控制强激光加热纳米粒子的爆炸/膨胀的影响。对于较小的纳米颗粒，流体和粒子单元(PIC)模型都可以预测到由强大的有重量动力引起的变形和压缩。对于更大的粒子(大于50纳米)和数百飞秒内的更长脉冲，烧蚀压缩似乎起到了作用。这些效应发生在一个独特的区域，即近场极限，其中激光波长远大于团簇大小。瑞利-泰勒不稳定性等问题不会出现在画面中，而且这种影响可能对带有热点的低质量激光不敏感。耐人寻味的可能性是，在亚波长空间尺度上，热致密物质的动力学可以通过适当定向和相移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，气体喷流产生的范德华星团的大小分布很可能完全掩盖了与粒子大小有关的效应。其次，喷流中的高星团密度将结果限制在总体平均水平。光束掠夺器和几何形状可以用来限制团簇密度，但团簇大小分布的问题仍然存在。所描述的方法将允许产生密度非常低的单一尺寸的纳米颗粒，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.