We have developed a high-repetition-rate time-, spin-, and angle-resolved photoemission spectroscopy (tr-SARPES) system that employs a 10.7 eV vacuum-ultraviolet laser generated from a Yb-doped fiber chirped-pulse-amplification source operating at 1 MHz. When combined with very-low-energy-electron-diffraction (VLEED) type spin polarimeter, the high-repetition-rate laser pulses effectively suppress space-charge broadening while enabling efficient spin detection, thereby overcoming the long-standing limitations of tr-SARPES. As a demonstration, we investigated the electronic structure of surface states including unoccupied states above the Fermi level on Bi(111), and achieved a direct, spin- and momentum-resolved visualization of pure spin currents generated immediately after photoexcitation in the topological insulator Sb2Te3. The present tr-SARPES apparatus provides a powerful platform for exploring opto-spintronics.
Kawaguchi et al. (Thu,) studied this question.