Femtosecond two-photon photoemission at 150 kHz utilizing two noncollinear optical parametric amplifiers for measuring ultrafast electron dynamics

An improved setup for femtosecond two-photon photoemission spectroscopy (TR-2PPE) is presented. Two noncollinear optical parametric amplifiers (NOPA) were operated simultaneously at a repetition rate of 150 kHz. The frequencies of the NOPA outputs were tuned such that subsequent second harmonic generation (SHG) provided the two different ultraviolet wavelengths required for the pump and probe pulse. The width of the crosscorrelation function (CC) for pump and probe pulse was sub-30 fs (FWHM). The performance of this assembly was tested by measuring the lifetime of image potential states (IS) on Cu(111) and Ag(111) surfaces. We present here for the first time lifetimes of the IS that were determined directly from the measured decay of the 2PPE signal.