Extraordinary momentum and spin discovered in evanescent light waves

http://phys.org/news/2014-03-extraordinary-momentum-evanescent.html

 

Paper Ref:

http://www.nature.com/ncomms/2014/140306/ncomms4300/full/ncomms4300.html

 

Abstract:

Momentum and spin represent fundamental dynamic properties of quantum
particles and fields. In particular, propagating optical waves (photons)
carry momentum and longitudinal spin determined by the wave vector and
circular polarization, respectively. Here we show that exactly the opposite
can be the case for evanescent optical waves. A single evanescent wave
possesses a spin component, which is independent of the polarization and is
orthogonal to the wave vector. Furthermore, such a wave carries a momentum
component, which is determined by the circular polarization and is also
orthogonal to the wave vector. We show that these extraordinary properties
reveal a fundamental Belinfante's spin momentum, known in field theory and
unobservable in propagating fields. We demonstrate that the transverse
momentum and spin push and twist a probe Mie particle in an evanescent
field. This allows the observation of 'impossible' properties of light and
of a fundamental field-theory quantity, which was previously considered as
'virtual'.

 

-Mark Iverson

 

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