Ultrafast Terahertz Light-Matter Interactions

该研究项目融合了超快激光科学和凝聚态物理，使用太赫兹（THz）频率光脉冲在亚皮秒时间尺度上测量和控制材料的电子自由度。在0.1 - 30thz的低能区，光与物质的相互作用主要是由自由和束缚电荷的运动、集体激发和在奇异态（如超导）中产生的低能隙所控制的。我们使用先进的非线性光学技术和飞秒激光源来产生相位稳定的，少周期的太赫兹脉冲光，允许这些激发的能量和时间分辨快照。我们使用我们的方法来帮助提供对新型太阳能电池材料的更好理解，其中太赫兹允许人们在光首次被吸收后，在无与伦比的亚ps时间尺度上同时定量测量光电性，激子和晶格动力学。我们将以新的有机金属卤化物钙钛矿材料为目标，这些材料已经席卷了太阳能社区，在那里，设备的快速发展超过了对材料本身的基本理解。相关电子材料表现出金属绝缘体跃迁，这种跃迁是由电子和晶格的相互竞争或合作导致的，这已经困扰了凝聚态物理学家几十年。太赫兹光谱学对金属态具有固有的敏感性，使我们能够在被光脉冲甚至另一个强太赫兹场触发后，在亚ps时间尺度上研究这些跃迁。通过它们不同的动态，分离每个贡献是可能的，从而提供对其涌现属性起源的深刻洞察。将锁相太赫兹脉冲的峰值电场和磁场强度分别提高到MV/cm和接近特斯拉的水平，可以通过与工程光场的相互作用，在亚周期时间尺度上实现对电荷和自旋激励的时域控制。这些极端场可以用来获取凝聚态物质中隐藏的自由度，我们将使用新开发的多维非线性太赫兹光谱仪来探索。最后，单周期，MV/cm脉冲通过克服半周期太赫兹脉冲场的功函数，允许从金属表面产生超短的高能电子爆发。我们将研制一种由太赫兹光场控制电子脉冲持续时间、能量和动量的新型时间分辨电子能量损失谱仪。

This research program merges ultrafast laser science and condensed matter physics, using pulses of terahertz (THz) frequency light to measure and control electronic degrees of freedom in materials on sub-picosecond time scales. The light-matter interaction in this low energy 0.1 - 30 THz regime is dominated by the motion of free and bound charges, collective excitations and low energy gaps arising in exotic states such as superconductivity. We use advanced nonlinear optical techniques and femtosecond laser sources to generate phase stable, few cycle THz pulses of light that allow energy and time-resolved snapshots of these excitations. We use our methods to help provide an improved understanding of novel solar cell materials, where THz allows one to quantitatively measure photoconductivity, exciton and lattice dynamics simultaneously, on unmatched sub-ps time scales after light is first absorbed. We will target the new organometallic halide perovskite materials that have taken the solar community by storm, where the rapid development of devices outpaces the basic understanding of the materials themselves. Correlated electron materials exhibiting metal-insulator transitions resulting from competing or cooperating electronic and lattice contributions have puzzled condensed matter physicists for decades. Intrinsically sensitive to the metallic state, THz spectroscopy allows us to study these transitions on sub-ps time scales after they are triggered by an optical pulse or even another strong THz field. Separation of each contribution is then possible through their different dynamics, providing deep insight into the origin of their emergent properties. Increasing the peak electric and magnetic field strength of phase-locked THz pulses to MV/cm and near Tesla levels, respectively, enables a new method of time-domain control over charge and spin excitations on sub-cycle time scales, through interaction with engineered light fields. These extreme fields can be used to access hidden degrees of freedom in condensed matter that we will explore using a newly developed multi-dimensional nonlinear THz spectrometer. Finally, single-cycle, MV/cm pulses allow the generation of ultra-short bursts of energetic electrons from metal surfaces by overcoming the work function in the half-cycle of the THz pulse field. We will develop a new time-resolved electron energy loss spectrometer with electron pulse duration, energy and momentum controlled by THz optical fields. This program offers extensive training in ultrafast laser science, THz optics, materials physics and instrumentation development for 6 graduate students and numerous undergraduates with vibrant collaborations in Canada and abroad. Training emphasizes critical thinking, teamwork, communication and networking skills that support a successful research career in innovative areas of direct benefit to Canada.