Ultrafast Laser Matter Interactions

在拟议的研究计划中，将开展超快激光物质相互作用的基础科学和应用导向研究。在基础科学研究中，我们将集中在超快激光加热固体的前几皮秒的定量理解。在这个早期，固体可以被加热到几个电子伏特（eV），但保持固体密度。具有高能量密度的加热固体被称为暖致密物质（WDM），这是目前材料科学研究的前沿领域。极端条件下材料的研究引起了人们极大的科学兴趣，并被美国国家科学院和国家科学技术理事会确定为本世纪的优先研究领域。WDM的理解是重要的激光材料加工，其中有许多科学和工业应用，以及惯性聚变能源，这是一种安全的能源，没有碳排放和几乎无限的燃料供应。我们的实验平台是基于探测的性质的一个自由站立的靶箔加热超快激光脉冲。实验平台的设计是为了产生无温度和密度梯度的单态WDM，从而简化了实验结果与理论结果的比较。例如，对于厚度为30纳米的金纳米箔靶，由于弹道电子具有约100 nm的范围，因此通过弹道电子传输可以在整个纳米膜厚度上均匀加热。在最初的几百飞秒中，产生了具有固体密度、低离子温度和几个eV的高电子温度的单态温密金。固体密度在分解成膨胀的等离子体之前会持续几皮秒。由于非平衡WDM持续几皮秒，其性质可以通过用超快探针探测来详细地实验研究。我们计划利用阿尔伯塔大学和其他世界级设施的能力，包括魁北克高级激光光源（ALLS）的100 TW级激光系统以及加州的SLAC国家加速器实验室，通过开发最先进的诊断技术，使用超快THz、光学、X射线和电子探针研究WDM。以及SLAC独特的高亮度X射线自由电子激光（XFEL）系统。WDM理论对理论家提出了巨大的挑战，因为WDM对于凝聚态理论来说太热了，而对于传统的等离子体理论来说又太密集了。我们将与一组理论家合作，以应对这一挑战。我们对几种激光应用感兴趣，我们将继续在这些领域进行研究。我们已经对激光诱导前向转移（LIFT）进行了研究，这是一种激光打印技术，特别是研究了LIFT用于纳米纤维的潜力。我们已经证明了LIFT与转移功能的大小低于70纳米。我们已经进行了研究，以探讨使用飞秒激光脉冲的可行性，以调整硅环形谐振器的谐振频率永久。我们利用超快激光诱导放大和烧蚀过程实现了硅环形谐振腔的双向频率调谐。我们还成功地展示了具有高迁移率的肖特基势垒场效应ZnO晶体管。ZnO薄膜使用激光烧蚀在250摄氏度的相对较低的衬底加热温度下生产，这与柔性电子应用的衬底兼容。我们将通过更好地理解基本的物理过程来继续优化这些技术。

In the proposed research program, basic science and applications oriented research in ultrafast laser matter interactions will be carried out. In the basic science research, we will focus on the quantitative understating of the first several picoseconds of ultrafast laser heating of solids. At this early time a solid can be heated to several electron Volts (eV) but remain at solid density. A heated solid with high energy density is called Warm Dense Matter (WDM) which is currently a forefront area of study in material science. The study of materials under extreme conditions has generated enormous scientific interest and was identified by the National Academy of Sciences and the National Science and Technology Council in USA as a priority research area for this century. The understanding of WDM is important for laser material processing, which has many scientific and industrial applications, as well as Inertial Fusion Energy, which is a safe energy source that has no carbon emission and almost unlimited fuel supply.Our experimental platform is based on probing the properties of a free standing ultrathin target foil heated by an ultrafast laser pulse. The experimental platform is designed to generate single state WDM with no temperature and density gradients providing simplification in the comparison of results from experiments and theories. For example, for a gold nanofoil target of thickness of 30 nanometers, the uniform heating throughout the entire nanofilm thickness is made possible by ballistic electron transport because the ballistic electrons have a range of ~100 nm. Single state warm dense gold with a solid density, a low ion temperature and a high electron temperature of several eV is created in the first few hundred femtoseconds. The solid density lasts for several picoseconds before it dissembles into an expanding plasma. Since the non-equilibrium WDM lasts for several picosecond, its properties can be studied in detail experimentally by probing it with ultrafast probes. We plan to study the WDM using ultrafast THz, optical, X-ray and electron probes by developing state-of-art diagnostic techniques making use of the capabilities in U of Alberta and other world-class facilities including 100 TW class laser systems at the Advanced Laser Light Source (ALLS) in Quebec as well as at the SLAC National Accelerator Laboratory in California, and the unique high brightness X-ray Free Electron Laser (XFEL) system at SLAC. The theory of WDM presents a great challenge for theorists because WDM is too hot for condensed matter theories and too dense for traditional plasma theories. We will work together with a team of theorists to tackle this challenge.Several laser applications are of interest to us and we will continue to carry out studies in these areas. We have carried out studies on laser induced forward transfer (LIFT), a laser printing technique, in particular studying the potential of LIFT for nanofabrication. We have demonstrated LIFT with transferred features with sizes below 70 nm. We have carried out studies to investigate the feasibility of using femtosecond laser pulses to tune the resonant frequency of silicon ring resonators permanently. We have demonstrated bi-directional frequency tuning of silicon ring resonators by making use of the ultrafast laser induced amphorization and ablation processes. We have also successfully demonstrated Schottky barrier field effect ZnO transistors with high mobility. The ZnO thin films are produced using laser ablation at a relatively low substrate heating temperature of 250 degree C which is compatible with substrates for flexible electronics applications. We will continue to optimize these techniques through better understanding of the basic physical processes.