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QED and collective effects in vacuum and plasmas
Umeå University, Faculty of Science and Technology, Department of Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The theory of quantum electrodynamics (QED) was born out of an attempt to merge Einsteins theory of special relativity and quantum mechanics. Einsteins energy/mass equivalence together with Heisenberg's uncertainty principle allows for particle pairs to be spontaneously created and annihilated in vacuum. These spontaneous fluctuations gives the quantum vacuum properties analogous to that of a nonlinear medium. Although these fluctuations in general does not give note of themselves, effects due to their presence can be stimulated or enhanced through external means, such as boundary conditions or electromagnetic fields. Whereas QED has been very well tested in the high-energy, low-intensity regime using particle accelerators, the opposite regime where the photon energy is low but instead the intensity is high is still to a large degree not investigated. This is expected to change with the rapid progress of modern high-power laser-systems.

In this thesis we begin by studying the QED effect of photon-photon scattering. This process has so far not been successfully verified experimentally, but we show that this may change already with present day laser powers. We also study QED effects due to strong magnetic fields. In particular, we obtain an analytical description for vacuum birefringence valid at arbitrary field strengths. Astrophysics already offer environments where QED processes may be influential, e.g. in neutron star and magnetar environments. For astrophysical purposes we investigate how effects of QED can be implemented in plasma models. In particular, we study QED dispersive effects due to weak rapidly oscillating fields, nonlinear effects due to slowly varying strong fields, as well as QED effects in strongly magnetized plasmas. Effects of quantum dispersion and the electron spin has also been included in an extended plasma description, of particular interest for dense and/or strongly magnetized systems.

Place, publisher, year, edition, pages
Umeå: Umeå universitet. Institutionen för fysik , 2010. , 59 p.
Keyword [en]
QED, quantum electrodynamics, quantum plasmas, quantum vacuum
National Category
Fusion, Plasma and Space Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-35615ISBN: 978-91-7264-972-9 (print)OAI: oai:DiVA.org:umu-35615DiVA: diva2:345665
Public defence
2010-09-22, MIT-huset, MA121, Umeå universitet, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2010-09-01 Created: 2010-08-26 Last updated: 2010-09-01Bibliographically approved
List of papers
1. Using high-power lasers for detection of elastic photon-photon scattering.
Open this publication in new window or tab >>Using high-power lasers for detection of elastic photon-photon scattering.
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2006 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 96, no 8, 083602-083605 p.Article in journal (Refereed) Published
Abstract [en]

The properties of four-wave interaction via the nonlinear quantum vacuum is investigated. The effect of the quantum vacuum is to generate photons with new frequencies and wave vectors, due to elastic photon-photon scattering. An expression for the number of generated photons is derived, and using state-of-the-art laser data it is found that the number of photons can reach detectable levels. In particular, the prospect of using the high-repetition Astra Gemini system at the Rutherford Appleton Laboratory is discussed. The problem of noise sources is reviewed, and it is found that the noise level can be reduced well below the signal level. Thus, detection of elastic photon-photon scattering may for the first time be achieved.

Place, publisher, year, edition, pages
The American Physical Society, 2006
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-11970 (URN)10.1103/PhysRevLett.96.083602 (DOI)
Note
Also in Laser Focus World, http://lfw.pennnet.com/articles/article_display.cfm?article_id=252481; in Physics News Update http://www.aip.org/pnu/2006/768.html; in Photonics.com http://www.photonics.com/content/news/2006/March/29/63472.aspxAvailable from: 2007-03-17 Created: 2007-03-17 Last updated: 2017-12-14Bibliographically approved
2. Analysis of four-wave mixing of high-power lasers for the detection of elastic photon-photon scattering
Open this publication in new window or tab >>Analysis of four-wave mixing of high-power lasers for the detection of elastic photon-photon scattering
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2006 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 74, no 4, 043821-043831 p.Article in journal (Refereed) Published
Abstract [en]

We derive expressions for the coupling coefficients for electromagnetic four-wave mixing in the nonlinear quantum vacuum. An experimental setup for detection of elastic photon-photon scattering is suggested, where three incoming laser pulses collide and generate a fourth wave with a new frequency and direction of propagation. An expression for the number of scattered photons is derived and, using beam parameters for the Astra Gemini system at the Rutherford Appleton Laboratory, it is found that the signal can reach detectable levels. Problems with shot-to-shot reproducibility are reviewed, and the magnitude of the noise arising from competing scattering processes is estimated. It is found that detection of elastic photon-photon scattering may be achieved.

Place, publisher, year, edition, pages
The American Physical Society, 2006
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-11969 (URN)10.1103/PhysRevA.74.043821 (DOI)
Available from: 2007-03-19 Created: 2007-03-19 Last updated: 2017-12-14Bibliographically approved
3. An effective action approach to photon propagation on a magnetized background
Open this publication in new window or tab >>An effective action approach to photon propagation on a magnetized background
2009 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, no 3, 31001-31005 p.Article in journal (Refereed) Published
Abstract [en]

A new explicit analytical form of the dispersion relation for photon propagation in the presence of a strong background magnetic field is derived within the effective action framework. The dispersion relation is expressed in terms of well-known special functions, and the treatment is exact within the linearization procedure, the one-loop approximation, and the soft photon approximation. The results are incorporated in a kinetic spin plasma description for the purpose of studying quantum electrodynamical effects of strongly magnetized plasmas. The results are applied to astrophysical examples.

Place, publisher, year, edition, pages
IOP Publishing, 2009
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-29845 (URN)10.1209/0295-5075/87/31001 (DOI)
Available from: 2009-11-25 Created: 2009-11-25 Last updated: 2017-12-12Bibliographically approved
4. Short wavelength quantum electrodynamical correction to cold plasma-wave propagation
Open this publication in new window or tab >>Short wavelength quantum electrodynamical correction to cold plasma-wave propagation
2006 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, no 10, 102102-102107 p.Article in journal (Refereed) Published
Abstract [en]

The effect of short wavelength quantum electrodynamic (QED) correction on plasma-wave propagation is investigated. The effect on plasma oscillations and on electromagnetic waves in an unmagnetized as well as a magnetized plasma is investigated. The effects of the short wavelength QED corrections are most evident for plasma oscillations and for extraordinary modes. In particular, the QED correction allow plasma oscillations to propagate, and the extraordinary mode loses its stop band. The significance of our results is discussed.

Place, publisher, year, edition, pages
American Institute of Physics, 2006
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-11967 (URN)10.1063/1.2356315 (DOI)
Available from: 2007-03-17 Created: 2007-03-17 Last updated: 2017-12-14Bibliographically approved
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