8 ms·
New Property of Light Discovered
- ASTP001 7y agoCan waves wave angular momentum? This is really neat.
- nsajko 7y agoTransversal waves can: https://en.wikipedia.org/wiki/Angular_momentum_of_light https://en.wikipedia.org/wiki/Angular_momentum_of_light
- sand500 7y agoI think it is this one?: https://arxiv.org/abs/1901.10942 https://arxiv.org/abs/1901.10942
- nsajko 7y agoThe Science version has much more readable/viewable formatting and has a bit more references, though.
- _burmer 7y agoTLDR they changed a doughnut into a croissant.
- BillSaysThis 7y agoDid they use a cronut as the intermediate stage?
- rossdavidh 7y agoOk I'm upvoting both of you, I don't care what HN says.
- qu1mby 7y agoWhoa. Anyone have any ideas for use cases? The article mentions manipulating tiny materials - like what? How would that work?
- nsajko 7y agoSee "Laser Manipulation of Atoms and Particles" for an introduction to the subject: https://sci-hub.tw/10.1126/science.253.5022.861 https://sci-hub.tw/10.1126/science.253.5022.861
- mNovak 7y agoApplied to microwaves in particular, modulating wave properties is how we transfer data. New ways to pack more bits per Hz are always useful.
- TheGrassyKnoll 7y agoGet your patents now...
- madengr 7y agoProblem is OAM does not work for long distances.
- mNovak 7y agoCan you elaborate? I've seen OAM at the conferences but not super familiar
- madengr 7y agoAs the beam diverges, you need larger and larger receive antennas to discriminate between the modes, more aperture than you need to compensate for path loss. That seems to be why OAM research is now mmWave (better collimating) and more applicable to short range backhaul.
- mooman219 7y agoLooks like this could improve bandwidth of free space connections, like satellite or directed beams.
- cced 7y agoIs this torque in the same sense of the word as “ability to move objects”? Is StarTrek happening?
- cmpb 7y agoNo, it seems that I’m this case, the angular momentum of the light beam itself changes over time, a process that is typically referred to as (or driven by?) torque in classical mechanics, and so they used that term here as well. They call it “self-torque” (I believe) because it’s the light changing it’s own angular momentum. But I’ve not been involved with physics academia in several years, so take it with a grain of salt.
- thenickdude 7y agoYou can push objects with light, check out https://en.wikipedia.org/wiki/Solar_sail https://en.wikipedia.org/wiki/Solar_sail
- m463 7y agoI wonder if this will affect how we understand things about light, like the two-slit experiment.
- mattnumbers 7y agoWhen we discovered that neutrinos oscillate, we knew that they had mass because we were able to observe a change from within our frame of reference, implying a finite time dilation. I thought that light was unable to change its physical properties in time (as observed from our frame of reference) due to infinite relativistic time dilation. How is it possible that we can observe torque, a change in angular momentum, for a particle moving at the speed of light?
- abdullahkhalids 7y agoAll special relativity says is that if an object is moving at the speed of light, its motion will appear to be the same in every reference frame. That is all. It says nothing on what can happen to photons when they are interacted with other photons or or with other media. Photons have several internal properties and all of these can be manipulated, either in the lab or naturally. The polarization of photons can be changed by Faraday rotation for example. In cosmology, you might be aware of Hubble's law, which involves the changing of the frequency of light. I haven't read this paper or intend to, but here is a key quote > We demonstrate that the self-torque arises as a necessary consequence of angular momentum conservation during the extremely non-linear, non-perturbative optical process of high-order harmonic generation (HHG). In HHG, the interaction of an intense field with an atom or molecule leads to the ionization of an electronic wavepacket, which acquires energy from the laser field before being driven back to its parent ion, and emitting a high-frequency photon upon recollision. What they are saying essentially is that by interacting the light with matter they are able to generate the said torque.
- bladedtoys 7y agoI think the question comes from the following understanding: - change requires the passage of time. - particles moving at the speed of light relative to us have infinite time dilation and so no time passes from our point of view. - the article is talking about particles moving at the speed of light which under go change. I have the same (mis?)understanding and am curious how this can work as well.
- ganzuul 7y agoThey rediscovered circular polarization? ED: No, apparently polarization is called spin angular momentum in this context. OAM can take a range of twist-rates while spin is either right- or lef-handed. And to the mute person who thinks downvoting questions is helpful: please just go away.
- craftinator 7y agoHey, on HN we believe that complaining about downvotes is crass, so please just bend over and accept like the rest of us! Thanks. Please see HN rules for any additional questions.
- angel_j 7y agoI had a wild thought, not 6 months ago, that angular momentum in light could account for all the missing dark stuff in the universe. I didn't know science didn't know light had angular momentum.
- andischo 7y agoMight be some stupid questions, but maybe someone can enlighten me: Could this explain the Schrödingers cat experiment, i.e. the light moving through both of the two slits? If light has a self torque, a single beam of light could travel through both slits (almost) simultaneously depending on the torque. Also, can someone clarify whether every beam of light has self-torque? Or do you need to create a beam of light in a special way to achieve this property? If every beam of light has that property, wouldn't that mean that light doesn't travel in wave form, but rather in a wave-cylindrical form?
- AnimalMuppet 7y agoThat's the two-slit interference experiment. Schrodinger's Cat is completely different. And no, this has nothing to do with the double slit experiment. And no, not every beam of light has self-torque. You need to create it in a special way.
- AnimalMuppet 7y agoDo I understand this right? Light has angular momentum (long known). That angular momentum can change (new), which requires torque. But it's a beam of light putting torque on itself. Or, it's photons in a beam of light putting torque on other photons in a beam of light. Worse, it seems to be (if I understood the article correctly) that different parts (front and back) of the beam of light are torquing each other. How can they do that while still moving at the speed of light?
- a3n 7y agoThe forward speed is the speed of light, but the angular speed is ... the angular speed. It's two different properties and measurements. Disclosure: I probably don't know what I'm talking about.
- amelius 7y agoIs there a limit to angular speed, just as there is a limit to forward speed?
- raimonides 7y agoThat is such a good question!
- nabla9 7y agoTo make it clear: Photons have two different forms of angular momentum. Spin angular momentum (SAM) and orbital angular momentum (OAM). Radiated photon carries not only spin but also orbital angular momentum. That OAM must exist has been known some time but it was observed relatively recently (27 years ago). Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes https://journals.aps.org/pra/abstract/10.1103/PhysRevA.45.8185 https://journals.aps.org/pra/abstract/10.1103/PhysRevA.45.81... >Abstract > Laser light with a Laguerre-Gaussian amplitude distribution is found to have a well-defined orbital angular momentum. An astigmatic optical system may be used to transform a high-order Laguerre-Gaussian mode into a high-order Hermite-Gaussian mode reversibly. An experiment is proposed to measure the mechanical torque induced by the transfer of orbital angular momentum associated with such a transformation. > Received 6 January 1992 >DOI:https://doi.org/10.1103/PhysRevA.45.8185 https://doi.org/10.1103/PhysRevA.45.8185
- agumonkey 7y agowas OAM used in any way in applications even though it hasn't been observed properly ?
- abdullahkhalids 7y agoYes, people have used OAM to demonstrate various quantum information tasks. See this as an example https://journals.aps.org/pra/abstract/10.1103/PhysRevA.80.063831 https://journals.aps.org/pra/abstract/10.1103/PhysRevA.80.06...
- bayareanative 7y agoCould this encode additional classical bits (optical transceivers) and/or qubits (single-photon quantum key-distribution protocol)?
- tinborn 7y agoI find this theory fascinating to consider: all physical objects/abstractions at each order of magnitude (atoms to laniakeas) in spacetime (shared reality) are holons governed by a natural and pragmatic system (platonic ideals) with some degree of freedom collapsing along quantum-information received by differential co-observations. Those objects with the most appearent freedoms and power to act, we traditionally call alive, yet it seems all objects at all orders of magnitude have some amount of autonomy, especially our own bodies. Light, electrons, and energy all exist within what appears to be the information and language layer between holons co-observing relational quantum-information (like spacetime) where time is the rate of subjective information observation, and the limited speed of information/light results in what we see in response time witnessed as observation-intention/reaction-action/physical change. Question for any postmodernist: (I don’t know if there are any in the physics circles because it seems that postmodernism ideology which dominates the humanities has serverly diverged from physics in some fundamental theories, and I am trying to understand this gap in theory.) It seems postmodernism’s claims on subjective reality throwns out the theory of platonic ideals and renders it impossible to see the math and geometric uniformity of the universe; and cannot conceive of the law “information is indestructable” if all reality is subjective. Please help me understand what I fail to see. To continue, if objective reality only exists within the spacetime dimensions and additionally a subjective reality exists as a set of dimentions within the information/language/feeling dimensions but collapses as observers understand each other via communication, this could find explain some of the gaps between social philosophy (humanities) and natural philosophy (science). Note: I will likely come back to this post tomorrow to rewrite it.
- inflatableDodo 7y agoMade me think, I wonder if the photon pressure from a vortex beam of light will spin a target, as well as push it away?
- max_likelihood 7y agoI did a project during my undergraduate degree in physics which involved interfering three planar waves at 60 degrees from one another to create a hexagonal intensity pattern. The interesting thing was that at each of the 6 corners of the hexagon was a singularity (optical vortex) where the phase was undefined. At these points, the phase space was shaped like a spiral staircase (screw dislocation) and particles suspended there could actually be rotated. It was like an “optical wrench” if you will. On a small scale, planar waves can be modeled like flat sheets of paper traveling through space without any angular momentum (no twisting motion). Yet when these sheets hit an object from multiple angles with the right timing, they can actually cause the object to twist.
- kbwt 7y ago> On a small scale, planar waves can be modeled like flat sheets of paper traveling through space without any angular momentum (no twisting motion). They certainly have angular momentum, it just depends on the choice of origin. If you pick an origin along the peak ray of the plane wave, there will be no twist around that point. Just like with a particle traveling in free space.
- max_likelihood 7y agoUnfortunately, I don’t know enough to intelligently comment on this. I was largely under the guidance of my professor. However, I can tell you that in my modeling I used the paraxial approximation and that the light was linearly polarized. It was my understanding that only circularly polarized light carried intrinsic angular momentum (https://en.wikipedia.org/wiki/Spin_angular_momentum_of_light#Mathematical_expression https://en.wikipedia.org/wiki/Spin_angular_momentum_of_light...). Also, I would agree with you that in a uniform electric field, a single E vector in isolation would appear to produce a torque on a point some distance away. But if the rest of the field is considered, the net torque at that point would be zero, right?
- afturner 7y agoThis is unbelievably fascinating. Can anyone go into more detail?
- ryanthedev 7y agoThis sounds like refraction. Two beams traveling through the cloud. If you use a double prisim, you could achieve the same type of results.
- mNovak 7y agoRefraction is a linear effect. This is nonlinear because two waves enter the gas at f1 and leave at f2 (the photon momentarily energizes an electron in the gas, which collapses and releases a photon at another frequency)
- ryanthedev 7y agoYou cannot guarantee the angles at which they enter the gas. They also stated to using different wavelengths out of sync. Which would cause the angle of refraction to be different. Different angles of refraction lead to different changes of speed as they enter one medium to another. Also I'm not sure what you mean "the photon momentarily energizes". The photon has a constant amount of energy. A beautiful balance of kinetic vs potential energy.
- ryanthedev 7y agoWhat does this mean for the double slit experiment?
- lurquer 7y agoI could listen to Laura Rego Cabezas talk about physics all day long.
- deleted 7y ago[deleted]