Time-resolved photoemission apparatus achieving sub-20-meV energy resolution and high stability

The paper describes a time-and angle-resolved photoemission apparatus consisting of a hemispherical analyzer and a pulsed laser source. We demonstrate 1.48-eV pump and 5.92-eV probe measurements at the >= 10.5-meV and >= 240-fs resolutions by use of fairly monochromatic 170-fs pulses delivered from a regeneratively amplified Ti: sapphire laser system operating typically at 250 kHz. The apparatus is capable to resolve the optically filled superconducting peak in the unoccupied states of a cuprate superconductor, Bi2Sr2CaCu2O8+delta. A dataset recorded on Bi(111) surface is also presented. Technical descriptions include the followings: A simple procedure to fine-tune the spatio-temporal overlap of the pump-and-probe beams and their diameters; achieving a long-term stability of the system that enables a normalization-free dataset acquisition; changing the repetition rate by utilizing acoustic optical modulator and frequency-division circuit. (C) 2014 AIP Publishing LLC.