Ishida Y, Otsu T, Ozawa A, Yaji K, Tani S, Shin S, Kobayashi Y
ISSP, University of Tokyo, Kashiwa-no-ha, Kashiwa, Chiba 277-8581, Japan.
Rev Sci Instrum. 2016 Dec;87(12):123902. doi: 10.1063/1.4969053.
The paper describes a time-resolved photoemission (TRPES) apparatus equipped with a Yb-doped fiber laser system delivering 1.2-eV pump and 5.9-eV probe pulses at the repetition rate of 95 MHz. Time and energy resolutions are 11.3 meV and ∼310 fs, respectively, the latter is estimated by performing TRPES on a highly oriented pyrolytic graphite (HOPG). The high repetition rate is suited for achieving high signal-to-noise ratio in TRPES spectra, thereby facilitating investigations of ultrafast electronic dynamics in the low pump fluence (p) region. TRPES of polycrystalline bismuth (Bi) at p as low as 30 nJ/mm is demonstrated. The laser source is compact and is docked to an existing TRPES apparatus based on a 250-kHz Ti:sapphire laser system. The 95-MHz system is less prone to space-charge broadening effects compared to the 250-kHz system, which we explicitly show in a systematic probe-power dependency of the Fermi cutoff of polycrystalline gold. We also describe that the TRPES response of an oriented Bi(111)/HOPG sample is useful for fine-tuning the spatial overlap of the pump and probe beams even when p is as low as 30 nJ/mm.
本文描述了一种时间分辨光发射（TRPES）装置，该装置配备了掺镱光纤激光系统，可在95 MHz的重复频率下产生1.2 eV的泵浦脉冲和5.9 eV的探测脉冲。时间分辨率和能量分辨率分别为11.3 meV和~310 fs，后者是通过在高度取向热解石墨（HOPG）上进行TRPES测量估算得出的。高重复频率适合在TRPES光谱中实现高信噪比，从而便于研究低泵浦通量（p）区域内的超快电子动力学。展示了在低至30 nJ/mm的p值下多晶铋（Bi）的TRPES。该激光源结构紧凑，并与基于250 kHz钛宝石激光系统的现有TRPES装置对接。与250 kHz系统相比，95 MHz系统更不易受到空间电荷展宽效应的影响，我们在多晶金费米截止的系统探测功率依赖性中明确展示了这一点。我们还描述了即使在p低至30 nJ/mm时，取向Bi(111)/HOPG样品的TRPES响应对于微调泵浦光束和探测光束的空间重叠也很有用。
