Beam size

[khurrle]

So I got a new torch style greenie and it's incredibly bright but despite how much I like it the beam gets far bigger than I like the farther away it gets. I would say that at about 50 feet it's about the size of a baseball. I would like it to be between 1/2 and 1 inch at that distance and not much more.

How can I achieve this?

Thanks

 

[Sigurthr]

Divergence is the property of light that describes how much it spreads out over a distance. You laser has too high of a divergence for what you want. A Beam Expander (despite the name, this actually makes it have a lower divergence) can be added after the laser's aperture, and this will allow you to control how wide the beam is at a certain distance.

 

[Bionic-Badger]

Divergence is inversely proportional to the beamsize at aperture. Notice how your greenie has a really nice thin beam at the opening? Well, that's part of the problem. You'll need the beam expander, as mentioned above, to make the beam wider for better collimation.

 

[khurrle]

Okay, so where can I get one of these and about how much will it set me back?

I don't really understand how my 5mw greenie has such nice divergence but this one is so much worse.

 

[Sigurthr]

Well, beam expanders can be made from two plano-convex or bi-convex lenses and a piece of PVC tube (and some hot glue) or bought for >$50. Before you sink oney on it, perhaps you can measure the diameter of the beam right at the aperture of your laser? It is possible the collimation lens is improperly set and thus not focused to infinity (the place where you get the best divergence). One way to check the setting of the lens is by measuring the beam diameter at aperture.

 

[Ash]

Or simply adjust the focusing lens slightly further from the KTP (second) crystal to achieve better collimation. (if you focus the laser properly, you don't need a +$300 beam-expander)

Sometimes China lasers aren't set at the optimal focus for low divergence (as they are typically made hurriedly on an assembly-line.

 

[khurrle]

Well, I fiddled with the position of the focusing lens and got it a little better than it had been before but it's still not as tight as I would like it to be ( I'm pretty sure I got it as tight as possible. Is there another lens below the outermost one that can be adjusted?

Thanks for the responses

 

[Sigurthr]

No lenses deeper than that one can be adjusted to fix it any further. Also, messing with anything past that outer lens will likely kill your laser - MCAs don't like to be fiddled with.

 

[khurrle]

Good thing I didn't go any deeper.

Would getting a different or better collimating/focusing lens make any difference?

 

[Sigurthr]

Nope, all green dpss lasers have an internal beam expander built in to them, with the last lens functioning as a collimation lens. You see, the crystals inside require the beam to be less than the diameter of a human hair in order to work, so the internal beam expander's first lens is set to expand it out as wide as possible after the crystals. The second lens then collimates it. Since it is set as best as it can get by you now, changing the second lens won't really fix anything. All you can do now is add an external beam expander for better divergence.

Which laser is this, by the way, and where did you buy it?

 

[khurrle]

Alright then. Thank you all for your input. Quite frankly for the price I am understanding I'll be looking at I'll just buy a new module to put in it.

As was stated in another thread. That is what I get for not following the advice given and getting an eBay cheap-o

Lesson learned.

 

[khurrle]

Which laser is this, by the way, and where did you buy it?

Missed this in the first place...

This
532nm Green Laser Pointer (Torch Style) | eBay

Also after some contact with the seller they are going to send me a replacement module that is focusable in the hope that itll be better than this one. Ill update when its received.