Editing Time-resolved spectroscopy (section)

==Time-resolved photoemission spectroscopy and 2PPE==

Time-resolved photoemission spectroscopy<ref>A. Stolow, A. E. Bragg, and D. M. Neumark, Femtosecond time-resolved photoelectron spectroscopy, Chem Rev, 104 (2004) 1719 [https://dx.doi.org/10.1021/cr020683w]</ref> and [[Two-photon photoelectron spectroscopy|two-photon photoelectron spectroscopy (2PPE)]] are important extensions to [[photoemission spectroscopy]]. These methods employ a [[Femtochemistry#Pump–probe spectroscopy|pump-probe]] setup. In most cases the pump and probe are both generated by a pulsed [[laser]] and in the [[UV]] region. The pump [[Excited state|excites]] the atom or molecule of interest, and the probe [[ionizes]] it. The [[electrons]] or [[positive ions]] resulting from this event are then detected. As the time delay between the pump and the probe are changed, the change in the energy (and sometimes emission direction) of the photo-products is observed. In some cases multiple photons of a lower energy are used as the ionizing probe.