Ultrafast Laser Matter Interactions

在计划的研究项目中，将开展超快激光物质相互作用的基础科学和应用研究。在基础科学研究中，我们将重点关注超快激光加热固体的前几皮秒的定量理解。在这个早期阶段，固体可以被加热到几个电子伏特（eV），但仍保持固体密度。热致密物质是一种具有高能量密度的加热固体，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巨大的科学兴趣，并被美国国家科学院和国家科学技术委员会确定为本世纪的优先研究领域。了解WDM对激光材料加工具有重要意义，激光材料加工具有许多科学和工业应用，以及惯性聚变能，这是一种没有碳排放和几乎无限燃料供应的安全能源。我们的实验平台是基于探测由超快激光脉冲加热的独立超薄目标箔的特性。实验平台设计用于生成无温度和密度梯度的单态波分复用，简化了实验和理论结果的比较。例如，对于厚度为30纳米的金纳米箔靶，由于弹道电子的范围为~100纳米，因此通过弹道电子输运可以在整个纳米膜厚度上均匀加热。在最初的几百飞秒内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暖致密金。固体密度持续几皮秒，然后分解成膨胀的等离子体。由于非平衡波分复用持续数皮秒，用超快探针探测波分复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用复用。我们计划使用超快太赫兹，光学，x射线和电子探针来研究WDM，通过开发最先进的诊断技术，利用阿尔伯塔大学和其他世界级设施的能力，包括魁北克先进激光光源（ALLS）的100 TW级激光系统以及加利福尼亚SLAC国家加速器实验室，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，而对于传统的等离子体理论来说又太密。我们将与一组理论学家合作来应对这一挑战。几种激光应用是我们感兴趣的，我们将继续在这些领域开展研究。我们开展了激光诱导正向转移（LIFT）的研究，这是一种激光打印技术，特别是研究LIFT在纳米制造方面的潜力。我们已经演示了具有小于70纳米尺寸的转移特征的LIFT。我们研究了利用飞秒激光脉冲永久调谐硅环谐振器谐振频率的可行性。我们演示了利用超快激光诱导双相化和烧蚀过程实现硅环形谐振器的双向频率调谐。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。采用激光烧蚀法在相对较低的衬底加热温度（250℃）下制备ZnO薄膜，该温度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.