Bessel Beam 'Tractor Beam' Concept Theoretically Demonstrated 54
cylonlover writes "Last year, NASA revealed it was evaluating three potential 'tractor beam' technologies to deliver planetary or atmospheric particles to a robotic rover or orbiting spacecraft. At the time, the third of these, which involved the use of a Bessel beam, only existed on paper. Researchers at Singapore's Agency for Science, Technology and Research (A*STAR) have now proven the theory behind the concept, demonstrating how a tractor beam can be realized in the real world – albeit on a very small scale (abstract)."
"theoretically demonstrated" (Score:5, Funny)
Bessel Beam 'Tractor Beam' Concept Theoretically Demonstrated
theoretically demonstrated? does not compute... pc load letter... explode!
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Better (and longer) form:
Physical property demonstrated that (if extrapolated infinitely) would do cool things.
Apparently a "Bessel Beam" is a perfectly parallel laser. They demonstrated tiny amounts of net pull from hitting very small things with a sufficiently parallel laser. So if you could perfect the parallel aspect and put about 6 giga-universes of energy behind one, you'd get a Star Trek style tractor beam.
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Bessel Beam 'Tractor Beam' Concept Theoretically Demonstrated
theoretically demonstrated? does not compute... pc load letter... explode!
What's the matter, my good chum? Have you never heard of a simulation?
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the headline should have read, "Theory Behind Bessel Beam 'Tractor Beam' Concept Demonstrated in Lab'
So how long until the drones can be armed by this? (Score:4, Funny)
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Stanley Tweedle, Number 476329-43 Department 511 Level 4! Report to security!
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Stanley Tweedle, Number 476329-43 Department 511 Level 4! Report to security!
Former assistant deputy backup courier for the Austral B Heretics.
Any experts out there? (Score:3)
The article isn't very helpful and the paper is only available for sale.
In the article it states that Bessel beams are unlike laser beams which "diffract or spread out as they propagate". I know laser beams diffract but I didn't think they spread out (and that was the whole point of them).
Can anybody explain exactly what's going on here and why are the Bessel beams imparting force/energy on the objects toward the beam source?
Thanx,
myke
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I know laser beams diffract but I didn't think they spread out (and that was the whole point of them).
Since you don't understand that those are the same thing*, I suggest you go read wikipedia until you understand what diffraction is.
Okay, they're not the same thing -- diffraction is only one mechanism by which a beam can spread. Shine a laser beam through a lens some time to see another one demonstrated...
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Why shouldn't it spread out? Perfectly collimated laser light wouldn't spread out, but such a thing is impossible, so it does.
The AC you replied to isn't very nice, but he's right.
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And more importantly can we use them to produce real artificial gravity?
Re:Any experts out there? (Score:4, Funny)
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Can anybody explain exactly what's going on here and why are the Bessel beams imparting force/energy on the objects toward the beam source?
Thanx,
myke
Bessel beams [wikipedia.org].
Optical tweezing [wikipedia.org]
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I know laser beams diffract but I didn't think they spread out
They do spread out, but the divergence angle is really small, and it also depends on the type of laser - some of them don't produce very well focused light.
To understand why it helps to look at a simplified laser design, like the one diagrammed here [wikipedia.org], which uses a crystal rod for the resonating cavity (YAG in the diagram, or ruby in Maiman's original laser). The active medium is pumped by the flash lamp, and photons are generated randomly in the body of the crystal rod. Most of them exit immediately through
Re:Any experts out there? (Score:4, Informative)
The article isn't very helpful and the paper is only available for sale.
In the article it states that Bessel beams are unlike laser beams which "diffract or spread out as they propagate". I know laser beams diffract but I didn't think they spread out (and that was the whole point of them).
Diffract is the same as spread out over distance. The main thing about laser beams is that they are monochromatic (mostly), and with the proper construction, the beam that leaves the oscillation chamber is mostly in phase (other than laser "speckle"). The xy profile of the beam is another matter.
Most laser beams are constructed to have a mostly a gaussian profile which is really close to the diffraction-less bessel profile (both of which are unfortunately of infinite extent). The gaussian profile is a solution of the Helmholz harmonic oscillator pde in cylindrical coordinates using a paraxial (ray-tracing) approximation, and the Bessel profile is a solution that is a true plane wave (basically a better approximation). Of course you can't make either an gaussian or a bessel (they have infinite support), so it's only an approximation, and since it's an approximation, it will diverge (but slowly and bessel more slowly as it's a better approximation). Think of it as picking the goldilocks profile for the beam that's not too sharp on the edge (causing it to diffract away), and not too blurry and that the exact shape so that math works out so it has a constant envelope over time and distance.
Can anybody explain exactly what's going on here and why are the Bessel beams imparting force/energy on the objects toward the beam source?
From what I can tell it seems to be a bit complicated, but as I understand it the gist is that the laser beam creates an electromagnetic wave that interacts with the object's dielectric/magnetic permitivity and creates what is called a Poynting vector S = E x H (a cross product) which is a flux energy in a specific direction. By manipulating the relative polarlization of this laser beam (the Transverse Electric vs Transverse Magnetic components), you can create a situation where this cross-product vector is mostly pointing back to the source. So basically you set up a dipole in the object itself to help you. This effect is small, but if the time averaged beam profile is constant over distance so it doesn't have a z-gradient where it diverges so that the electric field is lower at greater distance (because you used a bessel beam profile), this small flux energy effect will have the tendency to drag the object towards the beam. If there was a z-gradient where the field was lower at greater distance because of diffraction, then that will probably counteract this effect and cause the object to be pushed out instead of tractor-ed in.
impossible to create (Score:5, Interesting)
From the article:
While true Bessel beams are impossible to create, as they would require an infinite amount of energy, ...
This would seem like a good reason not to use them, even in a government project.
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Thats what the sharks are fore.
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An infinite amount of energy in an infinity large space is impossible, but if you treat those as "approaching infinite" you'll find the net energy for a given area inside to be approaching zero.
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A-Ha! (Score:1)
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So my comment earlier today about using a tractor beam to haul in the SpaceX Dragon not so stupid after all!
Not so fast there bub: "Bessel beams are impossible to create, as they would require an infinite amount of energy"
We know the Universe doesn't contain that amount of energy...
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No we do not.
We do not know how much energy the Universe contains because we cannot observe the entire universe. Even if restricted to the "observable" universe we are unable to examine it all.
The observed universe is not finite either as we don't know how many humans there have been nor how much of the universe each one has observed.
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Pop quiz! What's infinity squared?
Beam up my dandruff Scotty. (Score:1)
The future of dandruff removal looks bright, the Besseltron beckons...
AFSTAR (Score:2)
I'm pretty sure that acronym should be AFSTAR, I've never heard of the word "for" being spelled with an asterisk.
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I guess someone just sees pathfinding algorithms wherever they go....
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... did someone just divide by zero in here?
File with Perpetual Motion & Travel to the Pas (Score:2)
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Oh look, you tried to be a smartass and put body text into the subject, and you got truncated, bitch!
(seriously, don't do that.)
The actual paper, freely accessible (Score:5, Informative)
Simpler method (Score:2)
Unfortunately, this won't work in a vacuum: In a uniform clear fluid medium with dielectric constant A, put a uniform clear flat object with dielectric constant B<A perpendicular to the light beam. Light shined through the object speeds up compared with its speed in the medium, and by conservation of momentum exerts a force toward the source of the light.
When the object moves through the medium, it is extracting energy/power from the beam. Because the object is moving, there are relativistic calculation
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Um, why wouldn't this work in a vacuum? They state that the beam hits particles and is scattered forward (as opposed to backward in regular scattering).
Thusly, individual particles are given momentum towards the source of the emitter. Seems like this would work best in a vacuum. imagine a probe uses a laser to vaporize part of an object, then this beam would shine on the vapor drawing it through the vacuum to a collector.
Sam
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Because in a vacuum the beam is already travelling at the maximum possible speed. The photons can only slow down when they enter the object.
That's the reason according to the GP's explanation. I don't think his explanation is actually correct (although it would work in limited circumstances).
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Wouldn't the photons exiting the object on the other side exert the same force in the opposite direction? Seems like this would only work for infinitely long objects. Or, if the object were at least long enough that it takes the photons a significant time to travel through it, one could maybe use it to pull it a little closer (while the front of the beam hasn't yet arrived at the end) and hold it there while the beam is active, and make it bounce back by stopping the beam.
(If this works at all; IANAP, I've
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One more thought, and sorry for replying to myself: If you constantly increased the intensity of the beam, you could probably keep pulling it. But to even maintain the position would require continuous power proportional to the distance you pulled the object in the first place.
The only problem with it is... (Score:2)
The only problem with it is, it requires a good supply of Transparent Aluminum.