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UK scientists develop tractor beam

By Tatarigami in Technology
Sun May 06, 2001 at 01:18:09 AM EST
Tags: Science (all tags)

Scientists working in Britain have developed a device which uses 'a helix of twisting laser light' to move microscopic objects within a two dimensional plane.

This BBC report describes a method which relies on the target object refracting a portion of the laser light, and causing it to move towards the centre of the beam, where the light is most intense. The laser can then be used to rotate or move the object in any direction, although the current version cannot raise or lower it, or alter its orientation in three dimensions. (It's going to need some refinement before we start routinely equipping starships with the device.)

Dr Kishan Dholakia of St Andrews University says the technique could be used to drive rotating parts in nanoscale engines for cheap technologies of the future. There is also a university press release available on the topic.

Objects used in the testing so far have included glass beads 1/100 the width of a human hair, tiny glass rods and a hamster chromosome. (The hamster was not available for comment.)


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UK scientists develop tractor beam | 22 comments (15 topical, 7 editorial, 0 hidden)
Helix of twisting laser light (3.00 / 8) (#2)
by ZanThrax on Sat May 05, 2001 at 06:24:54 PM EST

How, exactly, do you get twisty lasers?

Time for a new .sig

Twisty lasers (4.00 / 4) (#5)
by Tatarigami on Sat May 05, 2001 at 06:59:42 PM EST

A second article I found after writing up this story (dammitall, should have done more research) says the device uses two laser beams to create an interference pattern. I wish I was clued up enough on optical physics to say how that works, but I slept through most of my science classes...

[ Parent ]
duh (none / 0) (#22)
by barrym on Wed May 09, 2001 at 08:35:38 AM EST

haven't you seen Ghostbusters ?!

[ Parent ]
How it works (i think) (4.22 / 9) (#7)
by guffin on Sat May 05, 2001 at 07:41:28 PM EST

I don't do much optics, but from reading their research group's page, it looks as if they are using an optical gradient to do the rotation. Basically, look at figure 1A on the same page. See how some areas are more intense than others? If you shine the intense parts on a symmetric molecule, the molecule will want to be in the part of the beam that is less intense. If you set it up right, it should rotate.

They aren't really 'helical' beams. The lasers are of course, straight as, well, laser beams =D. However, by cleverly interfering beams, you can get 'helical' interference patterns: the more intense spots rotate through time and/or space. I think they used a plane wave and a Laguerre-Gaussian beam. Laguerre-Gaussian beams look like radial ripples of low and high intensity, like a stone dropped into a pond ( it's a little more complicated, but you're probably not intersted)

Like I said, optics isn't my area, so this may be BS.

Duh (5.00 / 1) (#8)
by guffin on Sat May 05, 2001 at 08:05:53 PM EST

I forgot to include a link to what optical gradients are. It's explained rather nicely on another of their pages.

[ Parent ]
optical tweezers (none / 0) (#10)
by joeyo on Sat May 05, 2001 at 09:15:34 PM EST

This sounds to me like an advanced example of optical tweezers.

The term "helical beam" does bother me slightly. I think they are refering a circular polarization of the light. If you polarize light either in a right handed or left handed circle (or elipse) the E and B fields spiral around each other, their vectors thus taking a helical path.


If that all doesn't convince you that the WTO is evil, perhaps you should consider the possibility that you are evil. -- Parent ]

no (4.00 / 1) (#12)
by guffin on Sat May 05, 2001 at 09:31:00 PM EST

circularly polarized light wouldn't cause anything to rotate, though. You parametrize the E vector as something like Eo * (cos(w*t) * i + cos(w*t) * j), where i & j are the unit vectors in the plane of propagation (assuming plane waves for simplicity) of the wave. You neglect the interaction of the B field with the particle because it's of the order Eo / c, c the velocity of light. Then, the force on the particle will be F=q * E, which is a radial force, not a torque.

[ Parent ]
Make sure you read well (3.60 / 5) (#9)
by PFlats on Sat May 05, 2001 at 08:32:44 PM EST

In my never-ending Brilliance, I quickly skimmed the end of the article, and exclitedly cliked on the links. Despite about five minutes of searching, I couldn't find any pictures of the lasers moving a hampster.

Then I went back here, and noticed the little word "chromosome". Whoops. Tiny difference, no?

--- "It's not that I'm lazy, it's that I just don't care." - Peter Gibbons, Office Space

A talk I recently attended. (3.83 / 6) (#11)
by tiamat on Sat May 05, 2001 at 09:24:56 PM EST

Given by a nobel prize winner (physics) (and no, I don't remember his name) was about using lazers to cool things off. Sounds silly, but it's acutally quite simple. The theory (and eventually, the machine in practise) used the known idea of red shift to cool a particle off.

All you have to do (and this is really simplified) is take two identical lazers and shoot them at the particle from opposite sides. The lazer that is acting against the direction of the particle's motion (due to the red shift) has more of an effect on the particles motion, slowing it. And then the other one has the same effect when it turns around. I believe they were able to get some stuff down to about 0.7 Kelvin. (To do that you use lots of sets of lazers to effect motion in all 3D.)

William Phillips (4.00 / 2) (#13)
by joeyo on Sat May 05, 2001 at 10:51:44 PM EST

I don't know if it's the same guy that you saw, but last year I attended a lecture given by Dr. William Phillips of NIST on the topic of Laser Cooling. I think there were two other scientists who shared the 1997 nobel prize in physics with him for lazer cooling and trapping. (too lazy to check with google right now).

Anyway, it was a really good talk. He threw lots of liquid nitrogen around :^)

If that all doesn't convince you that the WTO is evil, perhaps you should consider the possibility that you are evil. -- Parent ]

This comments rating, WTF? (4.00 / 1) (#17)
by delmoi on Sun May 06, 2001 at 06:22:28 AM EST

Ok, this seems like a perfictly good comment. A little info, and very topical. Yet it has a score of 1.5. It's not like joeyo's comment makes tiamat out to be an idiot who dosn't know what he's talking about or anything. So, why was this comment rated so low? Is there something I'm missing?
"'argumentation' is not a word, idiot." -- thelizman
[ Parent ]
Steven Chu..probably (5.00 / 1) (#18)
by scheme on Sun May 06, 2001 at 08:42:00 AM EST

You're talking about Steven Chu probably. He has also done similar things with lasers and dna molecules.

"Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. THAT'S relativity." --Albert Einstein

[ Parent ]
Routine (4.00 / 1) (#19)
by skavookie on Sun May 06, 2001 at 04:20:05 PM EST

Lasers have been used for cooling for some years now. I believe laser-cooling is in (relatively) widespread use in atomic clocks.

[ Parent ]
Whew... (none / 0) (#20)
by Armaphine on Mon May 07, 2001 at 10:46:42 AM EST

At least no mention of Wesley Crusher assisting on this project was made...

Question authority. Don't ask why, just do it.

Wesley Crusher (none / 0) (#21)
by Tatarigami on Mon May 07, 2001 at 06:48:12 PM EST

Well, trekkers are like big dogs -- friendly, unkempt, slobbery and passive. Until someone mentions the Ensign Who Shall Not Be Named, or the fact that the stardate system is inconsistant, or that verteron particles have been either the cause or the solution of every engineering problem in the final four seasons of Next Generation, and suddenly they're tearing your arm off and sullenly chewing it in front of you.

I've been working on my one-handed typing technique, but haven't perfected it yet.


[ Parent ]
UK scientists develop tractor beam | 22 comments (15 topical, 7 editorial, 0 hidden)
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