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Density matrix and space-time distributions of the electronic density and current at fast pulsed photoemission through a double quantum well

Within the framework of the density matrix method, general formulas obtained that are convenient for describing fast pulsed photoemission that occurs in a time less than or on the order of the times of relaxation processes inside the photocathode. Expressions for the elements of the density matrix are found by solving the kinetic equation that takes into account the alternating electromagnetic field of light pumping and inelastic scattering of electrons. The derived formulas are applied for the numerical-analytical study of a one-dimensional model of wave-like spatiotemporal modulation of a photoelectron pulse of suitable duration during its passage through a double-well quantum-well heterostructure deposited on a volumetric planar photocathode. This modulation is a quantum beat that occurs as a result of excitation and subsequent slow oscillatory decay of the superposition of the doublet of quasi-stationary states of the heterostructure. It is possible to provide prolongation of generation and even amplification of waves of charge density and current density of photoelectrons when the photocathode is exposed to a periodic sequence of light pulses.