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Schematic of energy levels involved in two photons absorption. In atomic physics, two-photon absorption (TPA or 2PA), also called two-photon excitation or non-linear absorption, is the simultaneous absorption of two photons of identical or different frequencies in order to excite an atom or a molecule from one state (usually the ground state), via a virtual energy level, to a higher energy ...
Electron excitation is the transfer of a bound electron to a more energetic, but still bound state. This can be done by photoexcitation (PE), where the electron absorbs a photon and gains all its energy [ 1 ] or by collisional excitation (CE), where the electron receives energy from a collision with another, energetic electron. [ 2 ]
The excitation of a system (an atom or molecule) from one excited state to a higher-energy excited state with the absorption of a photon is called excited-state absorption (ESA). Excited-state absorption is possible only when an electron has been already excited from the ground state to a lower excited state.
A photon with an energy equal to the difference E 2 − E 1 between the energy levels is released or absorbed in the process. The frequency ν at which the spectral line occurs is related to the photon energy by Bohr's frequency condition E 2 − E 1 = hν where h denotes the Planck constant .
One has to distinguish between quasi-resonant excitation and barrier excitation. For quasi-resonant conditions, the energy of the excitation is tuned above the ground state but still below the barrier absorption edge, for example, into the continuum of the first subband. The polarization decay for these conditions is much faster than for ...
Diagram of the Stokes shift between absorption and emission light spectra. Stokes shift is the difference (in energy, wavenumber or frequency units) between positions of the band maxima of the absorption and emission spectra (fluorescence and Raman being two examples) of the same electronic transition. [1]
Schematic representation of the absorption line shape of an electronic excitation. The narrow component at the frequency ω′ is the zero-phonon line and the broader feature is the phonon sideband. In emission, the relative positions of the two components are mirrored about the center of the zero-phonon line at ω′.
Photoexcitation is the production of an excited state of a quantum system by photon absorption. The excited state originates from the interaction between a photon and the quantum system. Photons carry energy that is determined by the wavelengths of the light that carries the photons. [1]