Hanle effect

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The Hanle effect, [1] also known as zero-field level crossing, [2] is a reduction in the polarization of light when the atoms emitting the light are subject to a magnetic field in a particular direction, and when they have themselves been excited by polarized light.

Contents

Experiments which utilize the Hanle effect include measuring the lifetime of excited states, [3] and detecting the presence of magnetic fields. [4]

History

The first experimental evidence for the effect came from Robert W. Wood, [5] [6] and Lord Rayleigh. [7] The effect is named after Wilhelm Hanle, who was the first to explain the effect, in terms of classical physics, in Zeitschrift für Physik in 1924. [8] [9] Initially, the causes of the effect were controversial, and many theorists mistakenly thought it was a version of the Faraday effect. Attempts to understand the phenomenon were important in the subsequent development of quantum physics. [10]

An early theoretical treatment of level crossing effect was given by Gregory Breit. [11]

Theory

Classical model

The classical explanation for this effect involves the Lorentz oscillator model, which treats the electron bound to the nucleus as a classical oscillator. When light interacts with this oscillator, it sets the electron in motion in the direction of its polarization. Consequently, the radiation emitted by this moving electron is polarized in the same direction as the incident light, as explained by classical electrodynamics.

Applications

Observation of the Hanle effect on the light emitted by the Sun is used to indirectly measure the magnetic fields within the Sun, see:

The effect was initially considered in the context of gasses, followed by applications to solid state physics. [12] It has been used to measure both the states of localized electrons [13] and free electrons. [14] For spin-polarized electrical currents, the Hanle effect provides a way to measure the effective spin lifetime in a particular device. [15]

The zero-field Hanle level crossings involve magnetic fields, in which the states which are degenerate at zero magnetic field are split due to the Zeeman effect. There is also the closely analogous zero-field Stark level crossings with electric fields, in which the states which are degenerate at zero electric field are split due to the Stark effect. Tests of zero field Stark level crossings came after the Hanle-type measurements, and are generally less common, due to the increased complexity of the experiments. [16]

See also

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References

  1. ↑ Kastler, Alfred (1974). "50 Jahre Hanle-Effekt: Rückblick und Vorblick" [50 year Hanle Effect: Review and Prospects]. Physik Journal (in German). 30 (9): 394–404. doi: 10.1002/phbl.19740300903 . ISSN   0031-9279.
  2. ↑ Lurio, Allen; deZafra, R. L.; Goshen, Robert J. (1964-06-01). "Lifetime of the First 1P1 State of Zinc, Calcium, and Strontium". Physical Review. 134 (5A): A1198–A1203. Bibcode:1964PhRv..134.1198L. doi:10.1103/physrev.134.a1198. ISSN   0031-899X.
  3. ↑ Zimmermann, Dieter (1975). "Determination of the lifetime of the 4p1/2-state of potassium by Hanle-effect". Zeitschrift für Physik A. 275 (1): 5–10. Bibcode:1975ZPhyA.275....5Z. doi:10.1007/bf01409492. ISSN   0340-2193. S2CID   119987034.
  4. ↑ Dupont-Roc, J.; Haroche, S.; Cohen-Tannoudji, C. (1969). "Detection of very weak magnetic fields (10−9 gauss) by 87Rb zero-field level crossing resonances". Physics Letters A. 28 (9): 638–639. Bibcode:1969PhLA...28..638D. doi:10.1016/0375-9601(69)90480-0. ISSN   0375-9601.
  5. ↑ Wood, R.W. (1912). "LXVII. Selective reflexion, scattering and absorption by resonating gas molecules". The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science. 23 (137): 689–714. doi:10.1080/14786440508637267. ISSN   1941-5982.
  6. ↑ Wood, R. W.; Ellett, A. (1923-06-01). "On the Influence of Magnetic Fields on the Polarisation of Resonance Radiation". Proceedings of the Royal Society A. 103 (722): 396–403. Bibcode:1923RSPSA.103..396W. doi: 10.1098/rspa.1923.0065 . ISSN   1364-5021.
  7. ↑ Rayleigh, L. (1922-11-01). "Polarisation of the Light Scattered by Mercury Vapour Near the Resonance Periodicity". Proceedings of the Royal Society A. 102 (715): 190–196. Bibcode:1922RSPSA.102..190R. doi: 10.1098/rspa.1922.0080 . ISSN   1364-5021.
  8. ↑ Hanle, Wilhelm (1924-12-01). "Über magnetische Beeinflussung der Polarisation der Resonanzfluoreszenz". Zeitschrift für Physik (in German). 30 (1): 93–105. Bibcode:1924ZPhy...30...93H. doi:10.1007/bf01331827. ISSN   0044-3328. S2CID   120528168.
  9. ↑ Hanle, W. (1925). "Die magnetische Beeinflussung der Resonanzfluoreszenz". Ergebnisse der Exakten Naturwissenschaften (in German). Berlin, Heidelberg: Springer Berlin Heidelberg. pp. 214–232. doi:10.1007/978-3-642-94259-4_7. ISBN   978-3-642-93859-7.
  10. ↑ J Alnis; K Blushs; M Auzinsh; S Kennedy; N Shafer-Ray; E R I Abraham (2003). "The Hanle effect and level crossing spectroscopy in Rb vapour under strong laser excitation" (PDF). Journal of Physics B . 36 (6): 1161–1173. Bibcode:2003JPhB...36.1161A. doi:10.1088/0953-4075/36/6/307. S2CID   250734473. Archived from the original (PDF) on 2016-03-03. Retrieved 2012-03-06.
  11. ↑ Breit, G. (1933-04-01). "Quantum Theory of Dispersion (Continued). Parts VI and VII". Reviews of Modern Physics. 5 (2): 91–140. Bibcode:1933RvMP....5...91B. doi:10.1103/revmodphys.5.91. ISSN   0034-6861.
  12. ↑ Pikus, G. E.; Titkov, A. N. (1991). "Applications of the Hanle Effect in Solid State Physics". The Hanle Effect and Level-Crossing Spectroscopy. Boston, MA: Springer US. pp. 283–339. doi:10.1007/978-1-4615-3826-4_6. ISBN   978-1-4613-6707-9.
  13. ↑ Karlov, N.V.; Margerie, J.; Merle-D'Aubigné, Y. (1963). "Pompage optique des centres F dans KBr" (PDF). Journal de Physique (in French). 24 (10): 717–723. doi:10.1051/jphys:019630024010071700. ISSN   0368-3842. S2CID   95183756.
  14. ↑ Parsons, R. R. (1969-11-17). "Band-To-Band Optical Pumping in Solids and Polarized Photoluminescence". Physical Review Letters. 23 (20): 1152–1154. Bibcode:1969PhRvL..23.1152P. doi:10.1103/physrevlett.23.1152. ISSN   0031-9007.
  15. ↑ van ’t Erve, O. M. J.; Friedman, A. L.; Li, C. H.; Robinson, J. T.; Connell, J.; Lauhon, L. J.; Jonker, B. T. (2015-06-19). "Spin transport and Hanle effect in silicon nanowires using graphene tunnel barriers". Nature Communications. 6 (1): 7541. Bibcode:2015NatCo...6.7541V. doi: 10.1038/ncomms8541 . ISSN   2041-1723. PMID   26089110.
  16. ↑ Bylicki, F.; Weber, H.G. (1982). "Zero-field Stark level crossing and Stark—Zeeman recrossing experiments in the 593 nm band of NO2". Chemical Physics. 70 (3): 299–305. Bibcode:1982CP.....70..299B. doi:10.1016/0301-0104(82)88099-3. ISSN   0301-0104.
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