Instead of using metamaterials, the Technion team proposes a waveguide made of materials with a property called birefringence to create the necessary optical effects. Birefringence, which occurs naturally in crystals such as quartz and calcite, describes materials that have multiple indices of refraction, depending on what direction light enters the material. Place a calcite crystal on a newspaper, and suddenly the image is doubled.
Segev and his group's design uses layers of materials with different types of birefringence, along with specially designed mirrors, to make a practical model for how negative radiation pressure might be achieved. In this waveguide, the group velocity would move in one direction and the phase velocity in the opposite. Most important, it includes a large gap between the layers. This gap, which does not interfere with the optical properties of the material, allows the introduction of particles to be pulled into the waveguide. "It's like a sandwich," Segev says.
The proposed design can use a variety of birefringent materials, which are widely available and contain no metal, so they don't rob light of much energy. Additionally, although the birefringent materials used would be only micrometers thick, the gap could be millimeters wide, enabling fairly large particles to be manipulated by light.
Viktor Podolskiy, a physicist at the University of Massachusetts Lowell who was not part of this research, says that both the metamaterial approach and the birefringence approach address different issues in the creation of negative radiation pressure and have different advantages and drawbacks. "Metamaterials are addressing a set of issues where you try to confine the light to smaller, special spaces," Podolskiy explains. In contrast, the birefringence approach "does the opposite. It brings negative refraction to the level of larger-scale objects." Both approaches could someday find applications.
Jack Ng, a research assistant professor of physics at the Hong Kong University of Science and Technology who worked on the tractor beam proposal involving charge induction, says that the study may have some interesting ideas but also some flaws. In particular, he says that although the group showed the energy transfer can be negative, they "did not show that the force can be negative." In other words, the particles may not move.
In any case, the idea of generating negative radiation pressure by any means exists largely on paper; Segev's lab does not even have the resources required to create its proposed waveguide. Segev says, however, that several companies can make the necessary materials, and the researchers hope to find a firm soon so they can test their design experimentally. Until then, particles will just have to wait to experience the feeling of being drawn toward the light.
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Add CommentShouldn't Tractor Beam be one word, "Tractorbeam". When I saw the headline, I thought it was going to be a farm tractor that could produce a beam. Now we know that the Russians have been spying on us. Where else could they have gotten that idea from other than the American movie, Star Trek? Why don't they just ask Captain Kirk to share the tractorbeam spects with them?
Reply | Report Abuse | Link to thisLoved the ending: "move toward the light!" -Brightened my day :)
Reply | Report Abuse | Link to thisAll he needs now is to find a nuclear wessel, and he's all set.
Reply | Report Abuse | Link to thisYou are right, but Captain Kirk would have to authorize that information to leave the ship, wouldn't he?
Reply | Report Abuse | Link to thisPhotons are massless but they do have momentum, which is a function of the phase velocity. The group velocity of the wave, being composed of a narrow spread of frequencies, determines the direction of propagation. The phase velocity is the property that transfers momentum.
Reply | Report Abuse | Link to thisUsing birefringent materials enables directional splitting of the wave. There doesn't seem to be any conflict in terms of conservation of momentum. While it wasn't explicitly mentioned, I would imagine that the part of the wave that increases the phase velocity in the direction of propagation is ignored. The interesting part that reverses the phase velocity is aligned with a channel where the particles to be pulled shall be located.
Because both of these components originate from the same source, things could get interesting if we consider the consequences of quantum entanglement. If the ignored part of the wave isn't pushing something will negative radiation pressure be applied to particles in the pertinent structure?
If I was a billionaire, I'd fund this experiment immediately because now I'm curious to know the answer.
This is brilliant! I am amazed by the creativity of Segev and his group. He's not asking for any materials that are too out of the ordinary. I, too, hope he gets funding soon so we can find out of this theory works in practice.
Reply | Report Abuse | Link to thisIn reference to Jack Ng's doubts about whether the force will be in the direction of energy transfer, can't that be ironed out within the same equations used to find the direction of energy transfer?
As a freshman physics honors student at Princeton in the 60's, I quickly realized that there were 2 kinds of fairly or very smart people. First, there were the folks like Ng, Segev, et al, and then there were folks like me who could understand the article above, but who could never contribute to the laboratory or theoretical work described above and who were better suited to a career in Medicine or Engineering. I still read every S.A. article with great comprehension, but never will regret my 35 years as a Pediatric Oncologist.
Reply | Report Abuse | Link to thisVery Cool Discovery...and thanks for the graphics;-)
Reply | Report Abuse | Link to thisThis will move what a dust mote? An atom?
Reply | Report Abuse | Link to thisWe need something capable of ripping a Klingon ship to shreds......
But otherwise very cool!
Can you attract something with a large electrostatic field, and will it work in a vacuum?
Reply | Report Abuse | Link to thisif we construct a surface made of ceramics, we might move a lubricated piece, like a membrane along a cylinderby with light( laser) . It could be used to focus a telescope by the light from a star, for example, by amplification. or for photography in the night and adjustment of focality by amplification of received light. or a series of membrane to have a stronger force
Reply | Report Abuse | Link to thisJack Ng has a point. Negative refractive index has been proven but not negative radiation pressure. The latter does not theoretically follow from the former. The net force and pressure will follow the direction of the photon's velocity, the same direction as the phase velocity. The group velocity is in the opposite direction. So what?
Reply | Report Abuse | Link to thisSegev says the transfer of energy follows the group velocity. There seems to be a confusion here. Energy is a scalar quantity. It doesn't have a direction in space. Force and velocity are vectors. They have both magnitude and direction in space. It doesn't make sense to equate the "direction" of energy transfer to a direction in space. They are not the same thing.
Jack Ng has a point. Negative refractive index has been proven but not negative radiation pressure. The latter does not theoretically follow from the former. The net force and pressure will follow the direction of the photon's velocity, the same direction as the phase velocity. The group velocity is in the opposite direction. So what?
Reply | Report Abuse | Link to thisSegev says the transfer of energy follows the group velocity. There seems to be a confusion here. Energy is a scalar quantity. It doesn't have a direction in space. Force and velocity are vectors. They have both magnitude and direction in space. It doesn't make sense to equate the "direction" of energy transfer to a direction in space. They are not the same thing.
Correction: The photon's velocity follows group velocity. Hence, also the direction of force and pressure.
Reply | Report Abuse | Link to thisPhase velocity is a misnomer. Phase speed is the appropriate term. It's not a vector. It's actually a product of scalar quantities: angular frequency, wavelength, energy and momentum.
I agree with Jack Ng. It will not produce a net negative pressure because to create negative pressure you have to beam the electromagnetic wave to a material with negative refraction index. That creates positive pressure and then a negative pressure when the group velocity moves in the opposite direction. They will cancel each other. The net pressure is zero.
This is the first time I could read information and make out the posting...it simple and basic, the formatted posting is good..Looks like another adventure is at hand..
Reply | Report Abuse | Link to thisWhen you type in tractorbeam the red line shows up and when you write tractor beam it does not and I love Star Trek
Reply | Report Abuse | Link to thisI found the article fascinating(ahem...)but the comments have all been of equal worth and have cheered me up,to be reminded that smart witty people like yourselves are still part of or connected to the scientific community gives me hope for the future! :)
Reply | Report Abuse | Link to thisThe proof will be when we see a Crookes Radiometer running backwards.
Reply | Report Abuse | Link to thisExcept that light isn't causing the Crookes Radiometer to move (not directly anyway).
Reply | Report Abuse | Link to thisif you were to consider magnetism to be polarized gravitation would there not be a functionality?
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