A new twist in the properties of light

April 25, 2014, RIKEN
Transverse force (red) and torque (blue) exerted on a particle (yellow sphere) in an evanescent field generated by total internal reflection in a glass prism. Credit: © 2014 Konstantin Bliokh, RIKEN Interdisciplinary Theoretical Science Research Group

Light has some well-established dynamical properties that have defined our understanding of electromagnetic radiation for over a century. Two of the most fundamental of these properties are that photons of light carry momentum in the direction of propagation, and a 'spin' about the propagation axis defined by the electromagnetic wave's circular polarization. These properties play critical roles in a range of everyday phenomena and experimental interactions between light and matter.

Konstantin Bliokh from the RIKEN Interdisciplinary Theoretical Science Research Group (iTHES) and Aleksandr Bekshaev and Franco Nori from the RIKEN Center for Emergent Matter Science have now made the remarkable discovery that a particular type of known as evanescent waves possesses unexpected dynamical properties that are in sharp contrast with previous knowledge about light and photons.

Evanescent waves are produced, for example, when light undergoes total internal reflection at a boundary with another medium. In such situations, the main is reflected back into the originating medium and an evanescent wave is produced in the second medium. The evanescent wave decays rapidly away from the boundary but can propagate along the interface.

By investigating the dynamic characteristics of evanescent waves, Nori's team discovered that the momentum and spin of these waves have transverse components that are oriented at right angles to the plane of propagation. Equally surprising, they also found that the transverse momentum, and not the transverse spin, is determined by the wave's —precisely the opposite to the dependence seen in normal light.

"Although these extraordinary properties seem to be in contradiction with what is known about photons," explains Bliokh, "we have shown that they reveal what is known as 'spin momentum'—an enigmatic quantity that was introduced more than 70 years ago to explain the spin of quantum particles."

The research team's analysis suggests that these extraordinary properties of evanescent waves do in fact manifest in light–matter interactions, potentially leading to effects that are impossible to achieve and observe using normal light. For example, exert a transverse force and a transverse torque on small particles, where the force is dependent on the circular polarization but the torque is not (Fig. 1).

"Such remarkable , revealed in very basic objects, offer a unique opportunity to investigate and observe fundamental physical features that were previously hidden in usual propagating light and were considered impossible," concludes Bliokh.

Explore further: Extraordinary momentum and spin discovered in evanescent light waves

More information: Bliokh, K. Y., Bekshaev, A. Y. & Nori, F. Extraordinary momentum and spin in evanescent waves. Nature Communications 5, 3300 (2014). DOI: 10.1038/ncomms4300

Related Stories

Researchers take magnetic waves for a spin

January 29, 2014

Researchers at New York University have developed a method for creating and directing fast moving waves in magnetic fields that have the potential to enhance communication and information processing in computer chips and ...

Metal surface can repel electric charges

January 8, 2013

(Phys.org)—Metals are known for being good electrical conductors. Due to this property, a stationary electric point charge placed outside a metal will cause the electrons in the metal to redistribute in such a way that ...

Emerging from the vortex

February 17, 2012

Whether a car or a ball, the forces acting on a body moving in a straight line are very different to those acting on one moving in tight curves. This maxim also holds true at microscopic scales. As such, a beam of electrons ...

Recommended for you

Tangled magnetic fields power cosmic particle accelerators

December 13, 2018

Magnetic field lines tangled like spaghetti in a bowl might be behind the most powerful particle accelerators in the universe. That's the result of a new computational study by researchers from the Department of Energy's ...

Stretched quantum magnetism uncovered by quantum simulation

December 13, 2018

By studying ultracold atoms trapped in artificial crystals of light, Guillaume Salomon, a postdoc at the Max-Planck-Institute of Quantum Optics and a team of scientists have been able to directly observe a fundamental effect ...

The secret life of cloud droplets

December 13, 2018

Do water droplets cluster inside clouds? Researchers confirm two decades of theory with an airborne imaging instrument.


Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (3) Apr 25, 2014
1 / 5 (1) Apr 27, 2014
If these "evanescent waves exert a transverse force and transverse torque on small particles."

Can you say tractor beams!!!

Apr 27, 2014
This comment has been removed by a moderator.
not rated yet Apr 28, 2014
"IMO This observation is closely related to continuous spin photon model, presented here. The photons escaping from material objects in form of evanescent waves obtain properties of dark matter particles. The dark matter phenomena manifest itself at the perimeter of galaxies too."

Severe cognitive dysfunction. Pity.
1 / 5 (1) Apr 28, 2014
The BB theory has presented us with the intractable concepts of dark matter, dark energy and accellerated expansion. Perhaps a decaying photon, due to absorption and reemission, gravitational lensing and other mechanisms causing the loss of photon energy over time is causing the background red shift.
not rated yet Apr 28, 2014
Severe cognitive dysfunction. Pity
Severe argumentation dysfunction. Unrecoverable.
Perhaps a decaying photon, due to absorption and reemission, gravitational lensing and other mechanisms causing the loss of photon energy over time
The observations don't fully support this view. The distant galaxies appear relatively larger and more luminous like during observation through milky glass, which may serve as an indicia, their photons are scattered into various directions, not just decayed. In addition, the discussion of BB theory is off-topic here.
not rated yet Apr 29, 2014
"Sharp contrast." "Precisely the opposite." These words signify that Art Winfree's law of coupled oscillators is at work. The waves are a simple two oscillator system, coupled in precise opposition to each other. This is the most basic Winfree pattern. Winfree, a bio mathematician, developed his mathematical law circa 1967 and applied it to biology. I have applied it to physics, in numerous Physorg posts, many of which involve superconductivity. The "unexpected" results here all arise from Winfree's law.
1 / 5 (1) May 05, 2014
It is the tiny decrease on forward momentum each time the photon hits a molecule or an atom and briefly interacts with the electron that causes redshift in the light spectrum.
The brief entrapment of the photon until it is again released on its path takes an infinitesimal amount of this momentum. The loss of momentum meaning loss of energy is then translated into increase in wave length, therefore red shift.
This is the cause of red shift seen on the spectrum of distant galaxies an other distant objects, not expansion of the space as the Bigbang theory hypothesise.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.