Liu Yangyang, Beetar John E, Hosen Md Mofazzel, Dhakal Gyanendra, Sims Christopher, Kabir Firoza, Etienne Marc B, Dimitri Klauss, Regmi Sabin, Liu Yong, Pathak Arjun K, Kaczorowski Dariusz, Neupane Madhab, Chini Michael
Department of Physics, University of Central Florida, Orlando, Florida 32816, USA.
Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011-3020, USA.
Rev Sci Instrum. 2020 Jan 1;91(1):013102. doi: 10.1063/1.5121425.
Characterizing and controlling electronic properties of quantum materials require direct measurements of nonequilibrium electronic band structures over large regions of momentum space. Here, we demonstrate an experimental apparatus for time- and angle-resolved photoemission spectroscopy using high-order harmonic probe pulses generated by a robust, moderately high power (20 W) Yb:KGW amplifier with a tunable repetition rate between 50 and 150 kHz. By driving high-order harmonic generation (HHG) with the second harmonic of the fundamental 1025 nm laser pulses, we show that single-harmonic probe pulses at 21.8 eV photon energy can be effectively isolated without the use of a monochromator. The on-target photon flux can reach 5 × 10 photons/s at 50 kHz, and the time resolution is measured to be 320 fs. The relatively long pulse duration of the Yb-driven HHG source allows us to reach an excellent energy resolution of 21.5 meV, which is achieved by suppressing the space-charge broadening using a low photon flux of 1.5 × 10 photons/s at a higher repetition rate of 150 kHz. The capabilities of the setup are demonstrated through measurements in the topological semimetal ZrSiS and the topological insulator SbGdTe.
表征和控制量子材料的电子特性需要在动量空间的大区域内直接测量非平衡电子能带结构。在此，我们展示了一种用于时间和角度分辨光电子能谱的实验装置，该装置使用由一个稳健的、中等高功率（20瓦）的Yb:KGW放大器产生的高次谐波探测脉冲，其重复频率在50至150千赫兹之间可调。通过用1025纳米基频激光脉冲的二次谐波驱动高次谐波产生（HHG），我们表明在不使用单色仪的情况下，可以有效地分离出光子能量为21.8电子伏特的单谐波探测脉冲。在50千赫兹时，靶上光子通量可达到5×10个光子/秒，时间分辨率测量为320飞秒。Yb驱动的HHG源相对较长的脉冲持续时间使我们能够达到21.5毫电子伏特的出色能量分辨率，这是通过在150千赫兹的较高重复频率下使用1.5×10个光子/秒的低光子通量抑制空间电荷展宽来实现的。通过在拓扑半金属ZrSiS和拓扑绝缘体SbGdTe中的测量展示了该装置的能力。
