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Newly Discovered Optical Vortex Was Never Noticed Before

43 points by jwfxpr 10y ago

rcthompson 10y ago
I think the most intuitive explanation from the article was the analogy of a laser beam blowing smoke rings with light.
ChuckMcM 10y ago
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.
- effie 10y ago
  The laser creates a vortex ring, which is quite symmetrical - no net angular momentum needed.
jwfxpr 10y ago
Additional coverage here: http://www.sciencealert.com/scientists-have-discovered-new-smoke-rings-made-of-laser-light http://www.sciencealert.com/scientists-have-discovered-new-s...
biot 10y ago
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?
- jwfxpr 10y ago
  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.
PeterWhittaker 10y ago
This was found in a simulation. How would one detect this experimentally and confirm the phenomenon?
- wilsynet 10y ago
  Read the paragraph in the article that starts with "To check the simulations".
- jwfxpr 10y ago
  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.
  - PeterWhittaker 10y ago
    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.
est 10y ago
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?

43 points by jwfxpr 10y ago

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

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.

effie 10y ago
The laser creates a vortex ring, which is quite symmetrical - no net angular momentum needed.

jwfxpr 10y ago

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

biot 10y ago

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?

jwfxpr 10y ago
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.

PeterWhittaker 10y ago

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

wilsynet 10y ago
Read the paragraph in the article that starts with "To check the simulations".
jwfxpr 10y ago
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.
- PeterWhittaker 10y ago
  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.

est 10y ago

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?