Achieving photophoretic trapping

[Thatlaserguy89]

This is a very weird concept to me. I have read several articles and papers concerning the topic at hand. I always see a very confusing diagram like the one below

But then i see videos like this

Which make it seem very simple. Is it just a low wavelength laserbeam that traps a particle you put in it because of the focused beam? How focused does it need to be and how important is power because from what i read people are only using 5-25mW which is insanly small. Lets say i had a 405nm laser what would the power output meed to be and the focal length and density to achieve this trapping? Finally what are good materials, i see some that are markers but they burn up quick. I also read about graphite but im not sure. Any help would be grateful to me amd this community!

 

[Benm]

It's a pretty neat feature, and doesn't require a lot of power. It does require a single mode laser and good optics though: In the video example a particle of (presumably soot) is captured in the 'waist' of the beam: the part where it is most narrow and optical density is highest.

I've tried to do it myself with red single mode lasers but with little success - perhaps the power was actually too high and just burned up the particle.

The latter really is a problem with this technology: it is actually used in research to trap living cells, usually with 1064 nm lasers afaik. One issue with it is 'opticution' - where you actually kill the cell because it absorbs some of the light and is heated to death.

 

[paul1598419]

For cell sorting you need to use much less power if you want to keep your cells viable. I could set this up, but for a lack of the optics necessary to adjust the beam waist in the near field. It is pretty cool to be able to capture particles like this and move them along by adjust the position of the beam waist.

 

[Thatlaserguy89]

It's a pretty neat feature, and doesn't require a lot of power. It does require a single mode laser and good optics though: In the video example a particle of (presumably soot) is captured in the 'waist' of the beam: the part where it is most narrow and optical density is highest.

I've tried to do it myself with red single mode lasers but with little success - perhaps the power was actually too high and just burned up the particle.

The latter really is a problem with this technology: it is actually used in research to trap living cells, usually with 1064 nm lasers afaik. One issue with it is 'opticution' - where you actually kill the cell because it absorbs some of the light and is heated to death.

So what was the power of your laser? I was thinking somewhere arpund 100mw to 200mw but let me know please. Also single mode so i can just get a nice high power green laser in that aspect. My plan is to expand the beam size to 16mm the use a culminating lens of f=25 to get a really nice trap but let me know what kind of laser you guys think i should get. Maybe some links to if you dont mind. (Also note im not rich and some lasers can be expensive haha)