Tractor Beam?

shreve912 writes: "No captured Romulan Birds of Prey just yet, but the beam consisting of a helix of twisting laser light is able to seize hold of objects as small as a protein molecule. Scientists believe it will be an invaluable tool for manipulating parts of living cells or components of micro-machines. Holodecks and Borg implants can't be far off! Check out the article."

Tell us what we want to know!

[Dancin_Santa]

The beam consists of a helix of twisting laser light which is able to seize hold of objects as small as a protein molecule.

So we know the approximate lower bound of the tractor beam's grip. What's the upper bound? Enquiring minds want to know!

Dancin Santa

Is this really a tractor beam?

[MulluskO]

A method has been developed that uses laser light to spin molecules.

Is this a tractor beam? I would think that to qualify as such it would need to draw the particles toward the source of the beam.

It does sound as if movement perpendicular to the laser is possible. So, maybe one day, with two of these focused on a single point, we could draw this point closer. I'll have to shift my vision of single-ray tractor beams to double-ray beams.

I think they did that on the Simpsons once, Homer was too fat for one beam to lift him. They're visionaries, down at FOX.

My optics are a little rusty

[dmatos]

but IIRC, in order to get any appreciable level of refraction, the object performing the refraction needs to be of the same order of magnitude as the wavelength of the waves being refracted. This means that, for example, a car would cause significant refraction in light of wavelengths of around 3 metres. That puts it firmly in the radio wave section of the spectrum.

Now, I may be wrong, but it seems to me that the longest wavelength laser still works in the infrared region of the spectrum, nowhere near the metre-range of radio waves, so no appreciable diffraction would occur to short-wavelength light on macroscopic objects.

Also, I would like to know why the more intense light would incinerate objects. The light is not being absorbed, therefore its energy of h_nu is not being converted to heat. If the photon is just being diffracted, then more photons would mean more diffracted photons, and more "rebound", but not more heat.

Re:Tell us what we want to know!

[ryants]

What's the upper bound?

Well, according to the article, it's all on the "microscopic level"... so my guess would be the upper bound and the lower bound are of the same order of magnitude.

Ryan T. Sammartino

Re:Is this really a tractor beam?

[Dancin_Santa]

They could possibly use three lasers with the same resonant frequency to "capture" microscopic objects at some point at which the nodes met. When the object is acted upon by another force (gravity), it would essentially bump into a wall of energy on all sides and be forced back into the low energy node. Adjusting frequencies could possibly move the low energy node space towards or away from any particular laser. But I don't know anything about physics so don't rely on me for that kind of stuff.

Dancin Santa

Short introduction to Optical Tweezers

[Anonymous Coward]

http://www.nbi.dk/~tweezer/introduction.htm

Re:Tell us what we want to know!

[caffeinated_bunsen]

Well, the principle of operation of this (which only rotates objects) and optical tweezers (which move objects but can't rotate them) requires that the object refract light. Strictly speaking, there is no upper bound. But in order to produce a noticable force on a macroscopic object, you'd need far more light (several orders of magnitude) than would be necessary to incinerate said object.

The force results from the object changing the direction of propagation of photons, and thus changing their momentum. The recoil from this change is what moves the particle. The force is on the same order of magnitutde as the radiation pressure on an opaque object.

Re:Tell us what we want to know!

[Dancin_Santa]

Will there then be no "tractor beam" technology? If the energy necessary to exert a force on a large object would burn that object, then this would not be a viable for anything other than microscopic movements. Bummer.

Are there any other forces that could be exerted in a focused manner (obviously this would rule out magnetism and gravity) that could be used to "latch onto" a generic object and direct it on a macroscopic level?

Dancin Santa