Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental technique for researching the electronic band structures of quantum materials. The technique utilizes the photoelectric effect to eject electrons from a material. During the photoemission process, the electron's energy and parallel momentum in the material are conserved, allowing us to map the electron states in energy-momentum space. Moreover, the photoemission spectrum contains many-body information, represented by the self-energy term in the spectral function.

Time-resolved ARPES (trARPES) is a variant of the ARPES technique. trARPES employs femtosecond pump-probe spectroscopy, allowing the study of light-induced quantum phenomena, such as excitons, Floquet states, quantum phase transitions, electron-coherent phonon coupling, and unoccupied states, in the time domain.