photoionize

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photoionization

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/11/21 13:48:02」(JST)

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Photoionization is the process that makes once-invisible filaments in deep space glow.

Photoionization is the physical process in which an ion is formed from the interaction of a photon with an atom or molecule.

Cross section

Not every photon which encounters an atom or ion will photoionize it. The probability of photoionization is related to the photoionization cross-section, which depends on the energy of the photon and the target being considered. For photon energies below the ionization threshold, the photoionization cross-section is near zero. But with the development of pulsed lasers it has become possible to create extremely intense, coherent light where multi-photon ionization may occur. At even higher intensities (around 10¹⁵ – 10¹⁶ W/cm² of infrared or visible light), non-perturbative phenomena such as barrier suppression ionization and rescattering ionization are observed.

Multi-photon ionization

Several photons of energy below the ionization threshold may actually combine their energies to ionize an atom. This probability decreases rapidly with the number of photons required, but the development of very intense, pulsed lasers still makes it possible. In the perturbative regime (below about 10¹⁴ W/cm² at optical frequencies), the probability of absorbing N photons depends on the laser-light intensity I as I^N . For higher intensities, this dependence becomes invalid due to the then occurring AC Stark effect.

Resonance-enhanced multiphoton ionization (REMPI) is a technique applied to the spectroscopy of atoms and small molecules in which a tunable laser can be used to access an excited intermediate state.

Above threshold ionization (ATI) is an extension of multi-photon ionization where even more photons are absorbed than actually would be necessary to ionize the atom. The excess energy gives the released electron higher kinetic energy than the usual case of just-above threshold ionization. More precisely, The system will have multiple peaks in its photoelectron spectrum which are separated by the photon energies, this indicates that the emitted electron has more kinetic energy than in the normal (lowest possible number of photons) ionization case. The electrons released from the target will have approximately an integer number of photon-energies more kinetic energy.

Tunnel ionization

When either the laser intensity is further increased or a longer wavelength is applied as compared with the regime in which multi-photon ionization takes place, a quasi-stationary approach can be used and results in the distortion of the atomic potential in such a way that only a relatively low and narrow barrier between a bound state and the continuum states remains. Then, the electron can tunnel through or for larger distortions even overcome this barrier. These phenomena are called tunnel ionization and over-the-barrier ionization, respectively.

See also

• Ion source

References

Further reading

• Uwe Becker; David Allen Shirley (1 January 1996). VUV and Soft X-Ray Photoionization. Springer Science & Business Media. ISBN 978-0-306-45038-9. 
• Cheuk-Yiu Ng (1991). Vacuum Ultraviolet Photoionization and Photodissociation of Molecules and Clusters. World Scientific. ISBN 978-981-02-0430-3. 
• Joseph Berkowitz (1979). Photoabsorption, photoionization, and photoelectron spectroscopy. Academic Press. ISBN 978-0-12-091650-4. 
• V. S. Letokhov (1987). Laser photoionization spectroscopy. Academic Press. ISBN 978-0-12-444320-4. 

English Journal

• Metal-enhanced luminescence of silicon quantum dots: effects of nanoparticles and molecular electron donors and acceptors on the photofading kinetics.

• Abualnaja KM1, Šiller L, Horrocks BR.
• Nanotechnology.Nanotechnology.2015 Apr 10;26(14):145704. doi: 10.1088/0957-4484/26/14/145704. Epub 2015 Mar 18.
• Alkyl-capped silicon quantum dots (SiQDs) show enhanced luminescence when drop cast as films on glass slides in mixtures with Ag or Au nanoparticles or the electron donor ferrocene (Fc). Metal enhancement of quantum dot photoluminescence (PL) is known to arise from a combination of the intense near-
• PMID 25785514

• Site-selective photoemission from delocalized valence shells induced by molecular rotation.

• Miron C1, Miao Q2, Nicolas C1, Bozek JD3, Andrałojć W1, Patanen M1, Simões G4, Travnikova O1, Ågren H5, Gel'mukhanov F6.
• Nature communications.Nat Commun.2014 May 9;5:3816. doi: 10.1038/ncomms4816.
• Due to the generally delocalized nature of molecular valence orbitals, valence-shell spectroscopies do not usually allow to specifically target a selected atom in a molecule. However, in X-ray electron spectroscopy, the photoelectron momentum is large and the recoil angular momentum transferred to t
• PMID 24809410

• Probing rapidly-ionizing super-atom molecular orbitals in C60: a computational and femtosecond photoelectron spectroscopy study.

• Mignolet B1, Johansson JO, Campbell EE, Remacle F.
• Chemphyschem : a European journal of chemical physics and physical chemistry.Chemphyschem.2013 Oct 7;14(14):3332-40. doi: 10.1002/cphc.201300585. Epub 2013 Aug 8.
• Super-atom molecular orbitals (SAMOs) are diffuse hydrogen-like orbitals defined by the shallow potential at the centre of hollow molecules such as fullerenes. The SAMO excited states differ from the Rydberg states by the significant electronic density present inside the carbon cage. We provide a de
• PMID 23929667

Japanese Journal

• Electron spectra of xenon clusters irradiated with a laser-driven plasma soft-x-ray laser pulse

• Namba Shinichi,Hasegawa Noboru,Kishimoto Maki,Nishikino Masaharu,Takiyama Ken,Kawachi Tetsuya
• Physical Review A 84(5), 053202-1-053202-5, 2011
• … The laser photon energy was high enough to photoionize 4d core electrons. …
• NAID 120005122657

• Soft x-ray driven femtosecond molecular dynamics

• Science 317(5843), 1374-1378, 2007-09
• … We used soft x-raybeams generated by high-harmonic upconversion of a femtosecond laser to photoionize anitrogen molecule, creating highly excited molecular cations. …
• NAID 80018152046

Related Links

• Photoionize - definition of photoionize by The Free Dictionary

photoionize (ˌfəʊtəʊˈaɪəˌnaɪz) or photoionise vb (tr) (General Physics) physics to cause to undergo or to undergo photoionization ... Disclaimer All content on this website, including dictionary, thesaurus, literature, geography, and ...

• Photoionization | Definition of Photoionization by Merriam ...

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