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A Few Examples of Optical Trapping






mfo

mfo

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Very interesting video. I would love to know what causes this phenomenon. +rep to you.
 
bobhaha

bobhaha

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All info is there!

For more information on optical trapping and some high resolution shots, see my blog entry at:
Optical Trapping and the Momentum of Light @ JWC.blog

These are a few short clips illustrating the phenomenon of optical trapping. Essentially, a felt tip marker is briefly burned just above the focal point of a ~250mW 650nm laser, releasing an extremely small particle. This is not the intersection between the laser and some smoke; it's an actual particle embedded in the laser beam.

Because radiation can exert pressure on objects, there is a set of force vectors always keeping the particle just above the waist of the beam. This phenomenon illustrates how light can behave as particles (photons) because the photons have momentum and are therefore able to impart forces onto objects. It is even possible to move the laser around gently and the particle will follow along.

-Adrian
 
Benm

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Very clear video!

I'm still wondering why it works so well with those markers, few other materials seem to work reliably. Perhaps its somehow sputters out some droplet of ink, the solvent evaporates and what remains gets trapped?
 
J

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Benm said:
I'm still wondering why it works so well with those markers, few other materials seem to work reliably. Perhaps its somehow sputters out some droplet of ink, the solvent evaporates and what remains gets trapped?
Click to expand...

That's one possibility; it certainly seems plausible. I've heard that very soft plastic is also effective, so I would imagine that pieces of the felt are just breaking off. You could see by taking some black felt and trying the same way. If it doesn't release particles as well, then it's probably the ink.
 
Benm

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Soft plastics could have plasticizers serving the same function to some degree - i suppose.

I've tried to replicate the results using various materials, but none worked as well as the markers in the videos. Things like electrical tape will allow you to catch a particle once in a while, but very far from the almost 100% successes displayed using these markers.
 
J

jwc

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Benm said:
Soft plastics could have plasticizers serving the same function to some degree - i suppose.

I've tried to replicate the results using various materials, but none worked as well as the markers in the videos. Things like electrical tape will allow you to catch a particle once in a while, but very far from the almost 100% successes displayed using these markers.
Click to expand...

Yup. I wonder if the particles being trapped in the case of the electrical tape are from the adhesive.

It appears that my video has been posted on Reddit, so whichever one of you did that: thanks! :)
 
Benm

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The actual particle probably is... or at least something rather carbon rich like soot or tar.

What's difficult is getting it trapped there - the beam doenst just trap any particle that floats through it. If that were the case it could easily trap particles from smoke by just blowing smoke slowly through the waist of the beam.

I suppose another aspect is that the particle has to be big enough to see... if you capture something much smaller than the wavelength, it might be trapped, but will hardly be visible. On the other end particles obviously get too heavy to remain trapped, so it seems to be a fine balance.
 
Bluefan

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You can buy an optical trapping kit,, if you don't want a new car. And with 330mW of 980nm it generates a whopping 1 pN! if everybody in the US (300 million) bought one, they could lift together a single grain of rice!
Impressive, isn't it?
 
Tech_Junkie

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Bluefan said:
You can buy an optical trapping kit,, if you don't want a new car. And with 330mW of 980nm it generates a whopping 1 pN! if everybody in the US (300 million) bought one, they could lift together a single grain of rice!
Impressive, isn't it?
Click to expand...

Looks like they are using the same principal for optical tweezers.





 
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