Ultrafast Laser Matter Interactions

在拟议的研究计划中，将开展面向基础科学和应用的超快激光物质相互作用研究。在基础科学研究中，我们将着重于对超快激光加热固体的前几皮秒的定量低估。在这个早期，固体可以被加热到几个电子伏特(EV)，但仍保持固体密度。具有高能量密度的受热固体被称为热致密物质(WDM)，它是当前材料科学研究的前沿领域。极端条件下的材料研究已经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。了解波分复用器对于激光材料加工以及惯性聚变能源都具有重要意义，激光材料加工具有许多科学和工业应用，惯性聚变能源是一种无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超快激光脉冲加热的自由超薄靶箔的性质的。该实验平台可以产生没有温度和密度梯度的单态波分复用器，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，由于弹道电子的范围为~100 nm，因此整个纳米膜厚度的均匀加热是通过弹道电子传输实现的。在最初的几百飞秒内，产生了具有固体密度、低离子温度和数eV高电子温度的单态温暖致密的金。固体密度在分解成膨胀的等离子体之前持续几皮秒。由于非平衡波分复用器持续了几皮秒，因此可以用超快探头探测它，从实验上研究它的性质。我们计划利用阿尔伯塔大学和其他世界级设施的能力，利用超快太赫兹、光学、X射线和电子探针来研究WDM，包括魁北克高级激光光源(ALLS)和加利福尼亚州SLAC国家加速器实验室的100 TW级激光系统，以及SLAC独特的高亮度X射线自由电子激光(XFEL)系统。波分复用理论对理论界提出了很大的挑战，因为波分复用对于凝聚态理论来说太热，对于传统的等离子体理论来说太密集。我们将与一个理论家团队合作，共同应对这一挑战。 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。我们开展了激光诱导前向转移(LIFT)这一激光打印技术的研究，特别是对LIFT在纳米制造中的潜力进行了研究。我们已经演示了尺寸小于70纳米的转移特征的提升。我们开展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研究。我们利用超快激光诱导的去核化和烧蚀过程，实现了硅环谐振器的双向调谐。我们还成功地展示了具有高迁移率的肖特基势垒场效应氧化锌晶体管。氧化锌薄膜是在250摄氏度的相对较低的衬底加热温度下使用激光烧蚀而成的，这与灵活的电子应用中的衬底兼容。我们将通过更好地了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.