Scientists have built a macroscopic tractor beam using laser light: ScienceAlert

Tractor beams make intuitive sense. Matter and energy interact with each other in countless ways throughout the universe. Magnetism and gravity are both natural forces that can pull objects together, so there is a kind of precedent.

But constructing an actual tractor beam is something else.

A tractor beam is a device that can move an object over a distance. The idea comes from a 1931 sci-fi story called SpaceHounds by IPC:

“There is such a thing as a beam screen, you kill-joy, and there are also lift or tractor beams – two things that I have tried to dope out and that you have provided
me Bronx cheers. The Titanians have had a tractor beam for ages – he totally doped me up on that one – and the Jovians have both. We’ll have them in three days, and it should be pretty easy to dope out the opposite of a tractor as well – a pusher or thrust beam.”

If science fiction had anything to say about it, tractor beams would already be common, and we could thank you Star Trek and Star Wars for their spread.

But tractor beams already exist, even if their range is only microscopic.

Microscopic tractor beams are used in devices called optical tweezers. Optical tweezers use lasers to move microscopic objects such as atoms and nanoparticles. They are used in biology, nanotechnology and in medicine.

These tractor beams work on microscopic objects, but are not strong enough to pull larger macroscopic objects.

Now a team of researchers has successfully demonstrated a macroscopic tractor beam. They published the paper explaining their work in the journal Optics Express. The title is “Macroscopic laser pulling based on the Knudsen force in rarefied gas,” and the lead author is Lei Wang from QingDao University of Science and Technology in China.

“In previous studies, the light pulling force was too small to pull a macroscopic object,” Wang said.

“With our new approach, the light pulling force has a much larger amplitude. In fact, it is more than three orders of magnitude larger than the light pressure used to power a solar sail, which uses the momentum of the photons to exert a small pushing force.”

A tractor beam demonstrated with green lasers.
(Optics)

This macroscopic tractor beam only works under special laboratory conditions, so it is a demonstration, not a practical development. At least not yet.

First of all, it works on purpose-built stuff: macroscopic graphene-SiO2 composite objects that the researchers built for the experiments.

Second, it operates in an obsolete gas environment, which has a much lower pressure than Earth’s atmosphere. Although that limits their effectiveness here on Earth, not all worlds have as much atmospheric pressure as our planet.

“Our technique provides a non-contact approach and long-range features, which may be useful for various scientific experiments,” Wang said.

“The rare gas environment we used to demonstrate the technique is similar to that found on Mars. Therefore, it may have the potential to one day manipulate vehicles or aircraft on Mars.”

Their device works on the principle of gas heating. A laser heats the composite objects, but one side is hotter than the other. Gas molecules on the back side receive more energy, which pulls the object. Combined with the lower pressure in the rarefied gas environment, the object moves.

The researchers built a torsional or rotating pendulum device made from their graphene-SiO2 composite structure to demonstrate the laser drag phenomenon. That demonstration made it visible to the naked eye. They used a different device to measure the effect.

“We found that the pulling force was more than three orders of magnitude larger than the light pressure,” Wang said. “In addition, the laser draw is repeatable, and the power can be adjusted by changing the laser power.”

Other researchers have tackled tractor beams in recent years with mixed results. NASA was interested in pursuing the idea of ​​using tractor beams to collect samples with the MSL Curiosity surface rover. One of Curiosity’s instruments is ChemCam.

It includes a laser that vaporizes rock or regolith and then a micro-imaging device to measure the components spectroscopically. But NASA wondered if a tractor beam could pull tiny particles from the vaporized sample into the rover for a more complete study.

A 2010 NASA NIAC presentation said: “If Tractor Beam Technology was included in a ‘ChemCam2’ to pull in dust and plasma particles, tractor beams could add a number of additional science capabilities:

  • laser desorption ion spectroscopy
  • mass spectrometry
  • RAMAN spectroscopy
  • X-ray fluorescence”

The same presentation said tractor jets could be used to collect particles from comet tails, ice plumes on Enceladus and even clouds in Earth’s atmosphere or other atmospheres.

It never came to fruition, but it illustrates how compelling the idea is.

This new research produced interesting results, although it is nowhere near an actual practical implementation. There is a lot of work and engineering needed before it even comes close to being practical.

Firstly, there must be a well-understood theoretical basis that describes how the effect works on objects of different sizes and shapes and with lasers of different power in different atmospheres.

The researchers know this, of course, but point out that it is still an effective demonstration of feasibility.

“Our work shows that flexible light manipulation of a macroscopic object is possible when the interactions between the light, the object and the medium are carefully controlled,” Wang said.

“It also shows the complexity of laser-matter interactions and that many phenomena are far from being understood on both macro and micro scales.”

The critical part is that this study moves tractor beams from the microscopic to the macroscopic. It is a significant threshold that is difficult to cross.

“This work extends the scope of optical pulling from the microscale to the macroscale, which has great potential in macroscale optical manipulations,” the authors write in their conclusion.

Spacecraft may well use tractor beams one day, but they are unlikely to look like they do in science fiction. Star Wars, Star Trekand Spacehounds of the IPC everyone has tractor beams in battle and conflict.

But in reality, they can prove to be valuable scientific tools.

This article was originally published by Universe Today. Read the original article.

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