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Room temperature multi-phonon upconversion photoluminescence in monolayer semiconductor WS2
摘要： Photon upconversion is an anti-Stokes process in which an absorption of a photon leads to a reemission of a photon at an energy higher than the excitation energy. The upconversion photoemission has been already demonstrated in rare earth atoms in glasses, semiconductor quantum wells, nanobelts, carbon nanotubes and atomically thin semiconductors. Here, we demonstrate a room temperature upconversion photoluminescence process in a monolayer semiconductor WS2, with energy gain up to 150 meV. We attribute this process to transitions involving trions and many phonons and free exciton complexes. These results are very promising for energy harvesting, laser refrigeration and optoelectronics at the nanoscale.
关键词： photoluminescence,monolayer semiconductor,phonons,energy gain,room temperature,WS2,excitons,trions,upconversion
更新于2025-09-23 15:22:29
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Net energy gain in direct laser acceleration due to enhanced dephasing induced by an applied magnetic field
摘要： Even in the situation where an electron interacts with a single plane wave, the well-known dynamical adiabaticity can be broken when an applied magnetic field is present, which will act to increase the dephasing rate of the electron during the interaction. Here we demonstrate this for the case where there is a uniform static magnetic field which is oriented either parallel or perpendicular to the electric field of the incident plane wave, and perpendicular to the direction of its propagation. The described energy gain phenomenon has direct relevance to laser-plasma interactions that involve external magnetic fields generated by laser-driven capacitor coils.
关键词： net energy gain,direct laser acceleration,magnetic field,laser-plasma interactions,dephasing
更新于2025-09-19 17:13:59
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Electron–Ion Recombination Effect on Electron Acceleration by an Intense Laser Pulse
摘要： Electron–ion recombination effect on electron acceleration by a high-intensity laser pulse propagating through a tunnel ionizing gas is investigated in order to observe the actual electron energy gain during acceleration. An intense short-pulse laser with a Gaussian radial pro?le propagates through a vacuum followed by gas. The point at which the peak of the pulse interacts with the electron is the initial point of the gas region. Tunnel ionization causes defocusing of the laser pulse due to high-density plasma formation on the propagation axis. The electron experiences an additional acceleration during the trailing part of the pulse and, thus, gains net energy. In the presence of electron–ion recombination, the laser pulse focuses more, and hence, the net energy gain is affected signi?cantly for speci?c parameters region. A model that self-consistently evolves the laser electron acceleration as it ionizes a neutral gas is presented. The model incorporates the electron–ion recombination effects for multiple ionization stage and for tempospatial variations in the neutral gas density appropriate for studying gas-jet system. The electron energy gain during acceleration is calculated in He gas, where the conditions are appropriate for recombination. It is found that for a given laser intensity, there is always an optimal spot size and focal position with respect to the gas jet, which minimizes the refraction and maximizes the acceleration length for higher energy gain of the electrons. The inclusion of electron–ion recombination is more realistic if the pulse duration is longer in a laser–gas-jet experiment.
关键词： Electron acceleration,gas-jet,energy gain,electron–ion recombination,intense laser pulse
更新于2025-09-11 14:15:04