Ultrafast time- and angle-resolved photoemission spectroscopy with 11 eV laser pulses

Time- and angle-resolved photoemission (tr-ARPES) is a powerful technique that measures the transient dynamics of band structure in various condensed matter systems. In a tr-ARPES setup, one laser pulse is used to pump the system to an excited state, and a subsequent ultraviolet pulse is used to probe the photoemitted electrons at different time delays after the arrival of the pump pulse. Most tr-ARPES measurements are carried out with low energy (6-7 eV) photons, limiting the measurement range of the momentum space. In other approaches, 20-30 eV photons through high-harmonic generation (HHG) processes are used at the cost of a worse energy resolution (> 70 meV) due to the large bandwidth of the HHG pulses. Here we report tr-ARPES measurements with time and energy resolutions of 250 fs and 16 meV, respectively, using intermediate 11 eV laser pulses. Extreme ultraviolet pulses were produced through a third harmonic generation of 346 nm (3.58 eV) femtosecond laser pulses in Xe gas. We will show tr-ARPES measurements taken on single crystals of a topological insulator Bi₂Se₃ and a two-gap charge density wave material ErTe₃. Our results will allow study of various materials that have interesting phenomena far away from the center of the Brillouin zone.