Multiphoton photoemission

At high laser intensities, which are easily reached by lasers with low repetition rate, many electrons may be emitted by one laser pulse. The interaction of the electrons leads to a broadening and shift of the energy distribution, commonly referred to as space-charge effects [13, 38]. In this intensity regime, multiphoton photoemission may be observed with electrons of kinetic energies of up to several tens of electronvolts [39]. 

Ultrafast Multiphoton Photoemission Microscopy of Solid Surfaces in Real and Reciprocal Space... 

In this chapter we describe advances in the femtosecond time-resolved multiphoton photoemission spectroscopy (TR-MPP) as a method for probing electronic structure and ultrafast interfacial charge transfer dynamics of adsorbate-covered solid surfaces. The focus is on surface science-based approaches that combine ultrafast optical pump probe excitation to induce nonlinear multi-photon photoemission (MPP) from clean or adsorbate covered single crystal surfaces. The photoemitted electrons transmit spectroscopic and dynamical information, which is captured by their energy analysis in real or reciprocal space. We examine how photoelectron spectroscopy and microscopy yield information on the unoccupied molecular structure, electron transfer and relaxation processes, light induced chemical and physical transformations and the evolution of coherent single particle and collective excitations at solid surfaces. 

The process of nonlinear multiphoton absorption enables spectroscopic examination of unoccupied states of solids and solid surfaces. Like its linear counterpart, multiphoton photoemission probes the initial states below the Fermi level, E, within an energy range defined by nfia — O = Eq, where n is the order of the nonlinear process, O is the work function of the sample and Eq is the positive binding energy of the initial state with respect to The MPP... 

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