Ultrafast Laser Matter Interactions

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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.