
Newly Discovered Optical Vortex Was Never Noticed Before - jwfxpr
http://physics.aps.org/articles/v9/105
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ChuckMcM
Ok, that is pretty cool, the paper is here:
[http://journals.aps.org/prx/pdf/10.1103/PhysRevX.6.031037](http://journals.aps.org/prx/pdf/10.1103/PhysRevX.6.031037)

I'm still trying to get my head around the idea of a wave propagating in such
a way that it imparts an angular momentum on things.

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effie
The laser creates a vortex ring, which is quite symmetrical - no net angular
momentum needed.

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biot
If the main light pulse is traveling at the speed of light and the vortex
travels with it, that implies that the vortex must have one edge traveling at
2x the speed of light... but that's not possible. How does this reconcile with
relativity?

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jwfxpr
From the article:

>The rotation around an optical vortex does not concern the direction of the
oscillating electric field (polarization), but rather its phase [1]. For
example, the maximum of the field might initially be located just above the
central axis of a light beam, and then a short time later it’s to the right of
the axis, then below. This rotating phase gives the light an orbital angular
momentum that can cause a charged particle within the beam to rotate.

So no matter or energy is traveling or transmitting faster than light; a
property of the system can be observed to change location faster than the
speed of light half of the time. Properties of an object can _change_ at a
rate faster than light could propagate in a vacuum, as long as they don't
carry information.

Imagine you are shining an incredibly powerful flashlight at the dark surface
of the moon. You cover the light with your hand, and then uncover it again. An
observer could record the edge of the shadow moving faster than light, but
this doesn't mean any physical laws have been broken. No information, energy,
or mass has moved faster than light.

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jwfxpr
Additional coverage here: [http://www.sciencealert.com/scientists-have-
discovered-new-s...](http://www.sciencealert.com/scientists-have-discovered-
new-smoke-rings-made-of-laser-light)

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est
Just saw world's largest air cannon few days ago

[https://www.youtube.com/watch?v=GHiTDsFTFQQ](https://www.youtube.com/watch?v=GHiTDsFTFQQ)

so basically, STOVs are like this but of photons?

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rcthompson
I think the most intuitive explanation from the article was the analogy of a
laser beam blowing smoke rings with light.

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PeterWhittaker
This was found in a simulation. How would one detect this experimentally and
confirm the phenomenon?

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jwfxpr
First line of the abstract:

>We present the first experimental evidence, supported by theory and
simulation, of spatiotemporal optical vortices (STOVs).

The experimental setup is diagrammed and explained in part III.A of the paper:

>In order to experimentally confirm the existence of STOVs, we image the
spatiospectral phase and intensity profiles of femtosecond laser pulses
midflight during their precollapse and postcollapse evolution in air.

Appendix A gives the experimental setup in enough detail for it to be
reproduced in a lab with the correct equipment.

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PeterWhittaker
Ah, thanks. I've got to slow down my scanning of articles.

Intriguing that the simulation and experiment match. Now I'm curious about
alternative explanations for the experimental findings.

