Ultrafast Terahertz Light-Matter Interactions

这项研究计划融合了超快激光科学和凝聚态物理，使用太赫兹(THz)频率光的脉冲在亚皮秒的时间尺度上测量和控制材料中的电子自由度。在0.1-30太赫兹的低能区域，光与物质的相互作用主要由自由电荷和束缚电荷的运动、集体激发和超导态等奇异态中的低能隙所主导。我们使用先进的非线性光学技术和飞秒激光光源来产生相位稳定、周期很少的太赫兹脉冲，从而可以获得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的理解，其中THz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导、激子和晶格动力学。我们将瞄准新的有机金属卤化物钙钛矿材料，这些材料已经席卷了太阳能社区，其中设备的快速发展超过了对材料本身的基本理解。由于相互竞争或合作的电子和晶格贡献，呈现出金属-绝缘体转变的相关电子材料几十年来一直困扰着凝聚态物理学家。由于太赫兹光谱对金属状态的本质敏感，它允许我们在光脉冲甚至另一个强太赫兹场触发这些跃迁后，在亚微秒的时间尺度上对它们进行研究。然后，可以通过它们不同的动态将每种贡献分开，从而深入了解它们的新兴属性的起源。将锁相太赫兹脉冲的峰值电场和磁场分别提高到mV/cm和接近特斯拉水平，通过与工程光场的相互作用，实现了一种在亚周期时间尺度上对电荷和自旋激发进行时域控制的新方法。这些极值场可以用来获得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这一点。最后，通过克服太赫兹脉冲场半周期中的功函数，单周期、mV/cm脉冲允许从金属表面产生超短的高能电子爆发。我们将开发一种新型的时间分辨电子能量损失光谱仪，其电子脉冲宽度、能量和动量由太赫兹光场控制。

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.