Laser-Induced Electron Emission from Solids: Many-Photon Photoelectric Effects and Thermionic Emission

A systematic study of the laser-induced electron emission from solids was attempted by studying both metals and insulators in the form of evaporated films and single crystals, using three different radiations (10 600, 6943, and 3472 Å) from a $Q$-switched laser, and measuring not only the intensity dependence of the electron emission, but also the energy distribution of the emitted electrons. The electron emission from Au, stainless steel, CsI, KI, and KCl can be explained in terms of (1) thermionic emission and (2) many-photon photoelectric effects. Two- and three-photon effects were observed, and their quantum yields were measured. The theory of two- and three-photon photoelectric effects is briefly developed by a perturbation calculation of the term $-\left(\frac{e}{m}\right)$ A·p of the interaction Hamiltonian, and the formal expressions are evaluated for a simple three-band model of a solid and for a model that treats the properties of a solid in an average way. The degree of agreement between theory and experiment is discussed. Using a laser and a conventional light source, two-photon photoelectric spectroscopy was performed in CsI, and the spectrum obtained is interpreted in terms of parity-forbidden and -allowed transitions.