Take a loom at this diagram enter image description here

You have probably heard of this before but im just curious what laser they are using to do this. They do t appear to be ionizing air. It seems the one laser is just for color on the particle but what is the other? I would like to try this at home and make a dot for fun but i dont quite understand whats going on here. Any ideas?

  • $\begingroup$ Any links? The description presented above seems so dumbed down it's impossible to acquire actual mechanism from it. It certainly wouldn't work presented like this. A set of four powerful lasers in a tetrahedral setup, working outside visible spectrum could move a particle in 3D through light pressure, but I certainly don't see how a single laser could achieve 3 degrees of freedom of motion. $\endgroup$
    – SF.
    Commented Oct 8, 2018 at 10:58

1 Answer 1


The full letter is here:


They have 4 lasers: an RGB beam (3 lasers) that provides colour and an invisible 405nm beam that traps the particle. The RGB beam is pretty self-explanatory: you shine a beam of the colour you want the line to be.

The trapping beam is more complicated, by using lenses with particular imperfections you can focus the beam so that there is a dark volume near the focal point. Particles in this volume will be kept there by the photophoretic force. There is more information in this paper:


Playing with invisible lasers can be pretty dangerous

  • 1
    $\begingroup$ I will have more questions in a little but before i ask away i want you and stack overflow to know that i build lasers a lot, and not the cheap easy kind haha. Rather very expense and extremely dangerous. The last one i built was 55cm long and used very low inductance doorknob capacitors to allow for very fast discharges in the co2 laser chamber which made a beam that when focused to a point achieved optical air breakdown. $\endgroup$ Commented Oct 8, 2018 at 14:15
  • $\begingroup$ So this 405nm laser beam i see that it has to be cw solid state but does wattage matter a whole lot. I see that the particles are trapped with thermal energy (correct me if im wrong) in which case wattage is important a lot. But what would be a good rating to start at? The mW range or actual W $\endgroup$ Commented Oct 8, 2018 at 14:38
  • $\begingroup$ So with a 405nm laser @250mw i can focus it down to a point. But from videos i saw you need to put the particle there so a guy touches a marker to the focused beam. Do i need to do something like this everytime or ... also if i use 405 which is red will shining a blue laser on it change its color truly? Doesnt make much sense $\endgroup$ Commented Oct 8, 2018 at 15:56
  • 1
    $\begingroup$ 405 should be UV or near UV, shouldn't be too visible. By the sound of it, they are using tungsten or cellulose particles and quite high laser powers: 3W for the best trapping though possible at 24mW the other paper was using 0.5-30mW, they also say that power is one of the most important factors for good trapping. $\endgroup$
    – Mike
    Commented Oct 9, 2018 at 10:51
  • $\begingroup$ So now when it comes to lenses can i just use a plano convex f=25.4 lens. And with tungsten or cellulose i imagine the particle stays around for quite a while $\endgroup$ Commented Oct 9, 2018 at 10:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.