Bad divergence on a 532nm

Hi guys,

Got a FP 200mW (will measure later but it looks about 80mW) keychain laser, the divergence is terrible, the dot is about an inch across at 15-20ft , i can adjust the focus but thats the smalles i can get the dot, is there anything i can do about it?

TIA

ped said:

Hi guys,

Got a FP 200mW (will measure later but it looks about 80mW) keychain laser, the divergence is terrible, the dot is about an inch across at 15-20ft , i can adjust the focus but thats the smalles i can get the dot, is there anything i can do about it?

TIA

Click to expand...

With a lot of green's you can. I have a couple cheap 532nm pens from ebay and if you remove the top cap you will see a black plastic tube that houses the lens. On all of the ones I've taken apart there has been a weak adhesive that if you turn it, the adhesive will loosen up. By turn the tube you can adjust the focus. This is how it is done on pens I'm not sure about your laser though.

Here is a picture: Link The module on the bottom left is out of a green pen, and you can see the black tube I'm talking about.

-Hope this helps

Edit: Sorry I went back and re-read your question. I guess I read it too fast initially, so this probably doesn't help.

Yeah, thanks for trying, ive managed to focus it but even at its sharpest forcus, distance divergence is terrible.

:bumpit:

Anyone any other ideas on how i can improve divergence?

ped said:

:bumpit:

Anyone any other ideas on how i can improve divergence?

Click to expand...

You may need a longer focal length Plano-convex lens.

Do this first.
Get a friend to help so they can measure or tell you when the spot is smallest.

Sight your laser on a flat surface at least 50 feet away from you.

Adjust the spot until it is the smallest it can be. The laser is now optimally collimated.

Now if you are not satisfied the only option is to buy a new lens

Thanks steve.
The lens nearest the output crystal, i need to move that further away you mean?

ped said:

Thanks steve.
The lens nearest the output crystal, i need to move that further away you mean?

Click to expand...

No. You need to move the plano-concave.
Since you don't know what a plano-convex [PCX] lens looks like look around the web. One side's flat the other curved positively. The other lens is either a biconcave or a plano-concave.
There is a slight chance that in place of the pcx lens a biconvex lens is used. I doubt it. But if there is just swap it for a pcx lens if you need too.

Look up Galilean laser beam expanders. This is what you green laser uses.

I'd say that's pretty typical. Even my CNI PGL-III-A green laser and a labby I have produce about the same amount of divergence as the cheap-o one you have. I was measuring a dot about 1.5cm wide at 30ft. It is nearly exactly in line with the 1.5mRad divergence rating of the laser (see this divergence calculator).

The smaller the beam at the aperture, the greater the divergence. It's the price we pay for a small beam. Still, the divergence you mentioned probably could be improved. I would not touch the lens near the crystals, unless you want to permanently ruin the laser. There is probably a lens in the front of the laser, which you can adjust to your needs.

Ok i'll check that out when i'm brave enough thanks guys.