Two-photon photoelectron spectroscopy
Time-resolved two-photon photoelectron (2PPE) spectroscopy is a time-resolved spectroscopy technique which is used to study electronic structure and electronic excitations at surfaces. The technique utilizes femtosecond to picosecond laser pulses in order to first photoexcite an electron.
Source: Wikipedia — Two-photon photoelectron spectroscopy (CC BY-SA 4.0)