Electron emission from metal surfaces due to the illumination of laser fields is of great interest due to its broad applications ranging from electron sources to quantum information processing to attosecond physics. It also offers fundamental insights into electron dynamics and electronic band structures of materials. This thesis analytically studies the effects of laser (wavelength or frequency, and field strength) and cathode surface conditions (with or without dielectric coatings) on photoemission from biased metal surfaces, by exactly solving one-dimensional (1D) time-dependent Schrodinger equation. Our study provides better understanding of photoemission dynamics, laser heating effects on photoemission, and two-color laser coherent control of photoemission with a dc bias, and it is useful for the design of more stable and efficient emitters.First, we study photoemission from a metal surface using an analytical quantum model. It is found that shorter wavelength lasers can induce more photoemission from electron initial energy levels further below the Fermi level and, therefore, yield larger quantum efficiency (QE). The dc field increases QE, but it is found to have a greater impact on lasers with wavelengths close to the threshold (i.e., the corresponding photon energy is the same as the cathode work function) than on shorter wavelength lasers. When the laser field increases, QE increases with the laser field strength in the longer laser wavelength range due to the increased contributions from multiphoton absorption processes. The quantum model is compared with classical three-step model, the Fowler-DuBridge model, and the Monte Carlo simulation based on the three-step model. Even though those models have very different settings and assumptions, it is found that the scaling of QE of our quantum model agrees well with other models for low intensity laser fields.Next, we study photoemission from metal surfaces with laser wavelengths from 200 to 1200 nm (i.e., ultraviolet to near infrared). It is found that QE can be increased nonlinearly by the non-equilibrium electron heating produced by intense sub-picosecond laser pulses. This increase of QE due to laser heating is the strongest near laser wavelengths where the cathode work function is an integer multiple of the corresponding laser photon energy. The quantum model, with laser heating effects included, reproduces previous experimental results, which further validates our quantum model and the importance of laser heating.We then present an exact analytical theory for field emission from dielectric coated cathode surfaces, by solving the 1D Schrodinger equation with a double-triangular potential barrier introduced by the coating. The condition under which the emission current density from the coated cathode can be larger than the uncoated case is identified. Our quantum model is also compared with a modified Fowler-Nordheim equation for a double barrier, showing qualitatively good agreement.We further extend the exact quantum model for electron emission from metal surfaces coated with an ultrathin dielectric to photoemission. It is also found that a flat metal surface with a dielectric coating can photoemit a larger current density than the uncoated case when the dielectric has smaller relative permittivity and larger electron affinity. Resonant peaks in the photoemission probability and emission current are observed as a function of dielectric thickness or electron affinity due to the quantum interference of electron waves inside the dielectric. Our model is compared with the effective single-barrier quantum model and modified Fowler-Nordheim equation, for both 1D flat cathodes and pyramid-shaped nanoemitters. While the three models show quantitatively good agreement in the optical field tunneling regime, the present model may be used to give a more accurate evaluation of photoemission from coated emitters in the multiphoton absorption regime.Finally, we analyze the quantum pathways interference in two-color coherent control of photoemission using exact analytical solutions of the time-dependent Schrodinger equation. The theory includes all possible quantum pathways and their interference terms. It is found that increasing the intensity ratio of the second harmonic (2Ï⁹) laser to fundamental (Ï⁹) laser results in less contribution from the Ï⁹ pathway (absorption of Ï⁹ photons only) and more contribution from multicolor pathway (simultaneous absorption of both Ï⁹ and 2Ï⁹ photons) and 2Ï⁹ pathway (absorption of 2Ï⁹ photons only), and therefore stronger pathways interference and increased visibility larger than 95%. Increasing bias voltages shifts the dominant emission to processes with lower-order photon absorption, which sequentially decreases the interference between the Ï⁹ and the 2Ï⁹ pathways, and between single-color and multicolor pathways, leading to two peaks in the visibility as a function of dc field.
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