Article on advance in laser tractor beams

"Andrei Rhode, a researcher involved with the project, said that existing optical tweezers are able to move particles the size of a bacterium a few millimeters in a liquid. Their new technique can move objects one hundred times that size over a distance of a meter or more."

Tractor beams come to life

From the article:

The device works by shining a hollow laser beam around tiny glass particles. The air surrounding the particle heats up, while the dark center of the beam stays cool.

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Interesting: It looks like they are using a 532 beam hollow beam, but why would that heat up air surrounding a particle? Afaik 532 light moves through air without significant absorption (you can see a green forest 50 miles away just fine from a tall building) - so what's going on here?

Benm said:

From the article:



Interesting: It looks like they are using a 532 beam hollow beam, but why would that heat up air surrounding a particle? Afaik 532 light moves through air without significant absorption (you can see a green forest 50 miles away just fine from a tall building) - so what's going on here?

Click to expand...

I think whats going on is that when the particle touches the beam it absorbs the light more than air would. As a result, it would cause air around the spot that the beam is touching to heat and expand. When it expands it pushes slightly on the particle in the other direction. Thats my understanding of whats going on. (I'm just speculating here)

--Hydro15

You could be right about that. Normally optical tweezers keep the object you're holding in the maximum brightness part of the beam. This setup seems to keep it in the minimum. It could be localized heating on the object, similar to how a crooke radiometer works.