Sub-nanosecond pump-probe analysis of metal targets during nanoparticle generation by laser ablation in liquid and air – Temporal and spatial laser pulses control towards productivity increase and nanoparticle size control

纳米粒子的合成已成为制造具有可调物理化学性质的纳米材料的关键技术。在各种NP合成技术中，液体脉冲激光烧蚀(PLAL)技术尤其引人注目，因为它在靶材和所生成的NP组成方面具有多功能性。在我们项目(428315411)的第一阶段，我们进行了泵浦-探测显微镜实验，研究了从脉冲撞击到空化气泡(CB)坍塌的动力学，时间范围从ps到µS。这些单脉冲的结果被用来解决PLAL的主要局限性。例如，亚ns双脉冲PLAL被用来降低NP双峰性。此外，该研究还调查了PLAL的生产率限制因素，如气泡和等离子屏蔽，以及扫描策略对扩大PLAL的意义。在前一个项目建立的基本PLAL工艺的基础上，我们的目标是研究PLAL中时间和空间脉冲整形的基本机制如何影响NP尺寸分布和生产率，以实现连续的高产NP生产。在第一个项目阶段，我们发现在双脉冲PLAL装置中延迟600ps的第二个脉冲可以减少NP双峰性。我们计划进一步探索这项技术，以及ns尺度的第二个时间帧(CB形成)，其中第二个脉冲可以影响散裂层的出现、NP的生长和合并。除脉冲间延迟外，峰值注量(J)对烧蚀效率和粒子尺寸分布也有直接影响。到目前为止，通量控制是通过改变激光脉冲能量来实现的，但我们建议将空间高斯光束修改为椭圆形轮廓，以增加相互作用面积，并以最有效的J处理靶材，使NP产量最大化。此外，使用衍射光学元件(DO)可以产生多个光束，从而降低重复率，并允许在增加脉冲间距离的情况下进行并行处理。对于技术有限的快速扫描系统来说，这确实是一种很有前途的替代方案，可以避免PLAL中的CB屏蔽，并最大限度地提高NP产量。我们将评估建议的用于Au和FeNi的PLAL设置，这两种材料具有不同的物理化学性质，允许研究在PLAL中实现时间和空间脉冲整形的基本机制，以优化NP尺寸分布和增加产量。我们的最终目标是研究和开发一种具有成本效益的空间和时间形状的PLAL装置，提供NP尺寸控制和连续的高生产率，达到工业应用所需的g/h规模。

The synthesis of nanoparticles (NPs) has become an essential technology for creating nanomaterials with adjustable physicochemical properties. Among various NP synthesis techniques, pulsed laser ablation in liquids (PLAL) is particularly remarkable due to its versatility in target materials and the resulting NP compositions. In the first phase of our project (428315411), pump-probe microscopy (PPM) experiments were conducted to examine the dynamics of PLAL, from pulse impact to cavitation bubble (CB) collapse, on a timescale ranging from ps to µs. These single pulse results were utilized to address the primary limitations of PLAL. For example, sub-ns double pulse PLAL was used to decrease NP bimodality. Additionally, the study investigated productivity-limiting factors of PLAL, such as bubble and plasma shielding, as well as the significance of the scanning strategy for scaling up PLAL. Building upon the fundamental PLAL processes established in the previous project, our objective is to investigate how fundamental mechanisms of temporal and spatial pulse shaping in PLAL affect NP size distribution and productivity, with the aim of achieving continuous high yield NP production. During the first project phase, we discovered that a second pulse delayed 600 ps in a double pulse PLAL setup can reduce NP bimodality. We plan to further explore this technique, as well as a second temporal frame at the ns scale (CB formation), where a second pulse can influence spallation layer emergence, NP growth, and coalescence. In addition to the inter-pulse delay, the peak fluence (J) has a direct impact on ablation efficiency and NP size distribution. Thus far, fluence control has been achieved by varying the laser pulse energy, but we propose modifying the spatial Gaussian beam into an elliptical profile to increase the interaction area and process the target at the most efficient J, maximizing NP production. Furthermore, the use of diffractive optical elements (DOEs) can generate multiple beams, reducing repetition rates and allowing for parallel processing with increased inter-pulse distance. DOEs represent a promising alternative to technologically limited faster scanning systems for avoiding CB shielding in PLAL and maximizing NP production. We will evaluate the proposed PLAL setups for Au and FeNi, two materials with different physicochemical properties that permit the study of fundamental mechanisms for implementing temporal and spatial pulse shaping in PLAL to optimize NP size distribution and increase production. Our final objective is to study and develop a cost-effective spatially and temporally shaped PLAL setup that provides NP size control and continuous high production rates reaching the g/h scale required for industrial applications.