A decomposition of light's spin angular momentum density

Alex J. Vernon; Sebastian Golat; Claire Rigouzzo; Eugene A. Lim; Francisco J. Rodríguez-Fortuño

doi:10.1038/s41377-024-01447-9

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A decomposition of light's spin angular momentum density

Original Articles

- A decomposition of light's spin angular momentum density
- Light: Science & Applications Vol. 13, Issue 8, Pages: 1578-1589(2024)
- Affiliations：
  
  1.Department of Physics, King's College London, Strand, London WC2R 2LS, UK
  2.London Centre for Nanotechnology, London, UK
- Author bio：
  
  Francisco J. Rodríguez-Fortuño (francisco.rodriguez_fortuno@kcl.ac.uk)
- Funds：
- DOI：10.1038/s41377-024-01447-9
  CLC：
- Received：06 November 2023，
  
  Revised：14 March 2024，
  
  Accepted：2024-04-07，
  
  Published Online：10 July 2024，
  
  Published：31 August 2024
- Accepted：
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Vernon, A. J. et al. A decomposition of light's spin angular momentum density. Light: Science & Applications, 13, 1578-1589 (2024).
DOI：

Vernon, A. J. et al. A decomposition of light's spin angular momentum density. Light: Science & Applications, 13, 1578-1589 (2024). DOI： 10.1038/s41377-024-01447-9.

摘要

Abstract

Light carries intrinsic spin angular momentum (SAM) when the electric or magnetic field vector rotates over time. A familiar vector equation calculates the direction of light's SAM density using the right-hand rule with reference to the electric and magnetic polarisation ellipses. Using Maxwell's equations

this vector equation can be decomposed into a sum of two distinct terms

akin to the well-known Poynting vector decomposition into orbital and spin currents. We present the first general study of this spin decomposition

showing that the two terms

which we call canonical and Poynting spin

are chiral analogies to the canonical and spin momenta of light in its interaction with matter. Like canonical momentum

canonical spin is directly measurable. Both canonical and Poynting spin incorporate spatial variation of the electric and magnetic fields and are influenced by optical vortices. The decomposition allows us to show that a linearly polarised vortex beam

which has no total SAM

can nevertheless exert longitudinal chiral pressure due to equal and opposite canonical and Poynting spins.

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references

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