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  2. Absorption cross section - Wikipedia

    en.wikipedia.org/wiki/Absorption_cross_section

    In the context of ozone shielding of ultraviolet light, absorption cross section is the ability of a molecule to absorb a photon of a particular wavelength and polarization. Analogously, in the context of nuclear engineering, it refers to the probability of a particle (usually a neutron ) being absorbed by a nucleus.

  3. Two-photon absorption - Wikipedia

    en.wikipedia.org/wiki/Two-photon_absorption

    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 ...

  4. Absorption (electromagnetic radiation) - Wikipedia

    en.wikipedia.org/wiki/Absorption_(electromagnetic...

    The mass attenuation coefficient (also called "mass extinction coefficient"), which is the absorption coefficient divided by density; The absorption cross section and scattering cross-section, related closely to the absorption and attenuation coefficients, respectively "Extinction" in astronomy, which is equivalent to the attenuation coefficient

  5. Einstein coefficients - Wikipedia

    en.wikipedia.org/wiki/Einstein_coefficients

    An absorption line is formed when an atom or molecule makes a transition from a lower, E 1, to a higher discrete energy state, E 2, with a photon being absorbed in the process. These absorbed photons generally come from background continuum radiation (the full spectrum of electromagnetic radiation) and a spectrum will show a drop in the ...

  6. Schwarzschild's equation for radiative transfer - Wikipedia

    en.wikipedia.org/wiki/Schwarzschild's_equation...

    The oscillator strength for any transition between ground and excited state depends on these coefficients. The absorption cross-section (σ λ) is empirically determined from this oscillator strength and the broadening of the absorption/emission line by collisions, the Doppler effect and the uncertainty principle.

  7. Feynman diagram - Wikipedia

    en.wikipedia.org/wiki/Feynman_diagram

    When calculating scattering cross-sections in particle physics, the interaction between particles can be described by starting from a free field that describes the incoming and outgoing particles, and including an interaction Hamiltonian to describe how the particles deflect one another. The amplitude for scattering is the sum of each possible ...

  8. Non-degenerate two-photon absorption - Wikipedia

    en.wikipedia.org/wiki/Non-degenerate_two-photon...

    To implement non-degenerate two photon excitation microscopy, two photon pulses of differing energies must be synchronized to interact with a specimen at the sample plane near-simultaneously. Due to the enhanced absorption cross section and VSL, more time is possible for excitation to occur, and thus perfect synchronization is unnecessary.

  9. McCumber relation - Wikipedia

    en.wikipedia.org/wiki/McCumber_relation

    The McCumber relation (or McCumber theory) is a relationship between the effective cross-sections of absorption and emission of light in the physics of solid-state lasers. [ 1 ] [ 2 ] It is named after Dean McCumber , who proposed the relationship in 1964.