Hacking a cheap laser module to get a divergent beam

My name is Luis Rodenas and this is my first post at this forum, so hello everyone.

First a few lines about my project: I am developing a small RC helicopter with a laser emitter that has to hit (with the laser beam) a static target. Rigth now I am using very cheap laser modules that I got from ebay (example picture below), they are very small (6 mm diameter), work at 3V and only have 1 plastic lens inside the copper head.

The thing is I want to get a much larger laser dot, divergent beam, in order to make it easier to hit the target while flying.



So far I achieved a 9 cm laser dot at 1 meter distance, but the dot brigthness is not uniform (half circle is darker) and I would like to get something closer to 15 cm at 1 meter distance.
I achieved this just flipping over the original lens while experimenting, no idea what kind of lens that is (collimating?) nor why it worked.

I want to do it the rigth way, so I am looking for better lenses or laser modules to match my needs. I am looking now at plano concave lenses.

My questions:
- Any idea what focal length and curvature more or less should have this plano concave lens?
- Should I keep the original lens (collimating?) and put behind the new lens? Or will it work only with the new lens?
- Do you know of any one who has worked on this matters or company doing divergent laser modules?
- Tips on how to achieve this?
- Should I better consider a high power led with a very narrow beam? Do you know if they even exist? I couldn't find narrow beam high power leds.

Lots of questions I know, but any little help or comment is much appreciated.
Thank you!

I'd recommend a 520nm or 515nm diode. It will be brighter and you can focus the dot size.

Thanks for the tip! At first I was also looking for green lasers since they were supposed to be brigther at same output power, but I couldn't find any cheap module or diode. Do you know of any?

What do you mean with "you can focus the dot size"? Isn't that something independent of the wavelength used?

luisonoff said:

Thanks for the tip! At first I was also looking for green lasers since they were supposed to be brigther at same output power, but I couldn't find any cheap module or diode. Do you know of any?

What do you mean with "you can focus the dot size"? Isn't that something independent of the wavelength used?

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Depends how you define cheap - they are never going to be as cheap as those little red modules you've got. eBay should have plenty of green modules though. A whole bunch come up if you search "Green Laser Module" there. Someone else may have a better source - things can be hit or miss with eBay.

Yes - it is independent of wavelength. But chances are if you are buying a 515nm or 520nm module that it'll be in an Aixiz housing which has an adjustable focus unlike some of those really cheap red modules. I think that's what he was getting at... I could be wrong

Thank you diachi for the extra explanation.
I just searched on Ebay and found some USD10 green laser modules, which is 100x more expensive than the red ones, but ok.
My concern is that every green laser I find is larger in size and higher power (30mW) than the ones I am looking for.
I need a laser module or standalone laser diode that is small, something like 6mm diameter, and very low power, 5-10 mW max. Then I guess if I get this small ones, they wont come with that Aixiz housing that enable to enlarge the dot, so I have to look for another solution to get the 15cm diameter dot at 1 meter distance that I am looking for.
Any extra ideas anyone??

luisonoff said:

Thank you diachi for the extra explanation.
I just searched on Ebay and found some USD10 green laser modules, which is 100x more expensive than the red ones, but ok.
My concern is that every green laser I find is larger in size and higher power (30mW) than the ones I am looking for.
I need a laser module or standalone laser diode that is small, something like 6mm diameter, and very low power, 5-10 mW max. Then I guess if I get this small ones, they wont come with that Aixiz housing that enable to enlarge the dot, so I have to look for another solution to get the 15cm diameter dot at 1 meter distance that I am looking for.
Any extra ideas anyone??

Click to expand...

In that case you'd probably need to use an external lens to expand the beam. I'm not aware of any 532nm modules that small unfortunately and I haven't seen any 520nm modules at that size either - although I'm sure the latter would be doable.

I'm sorry if I was not clear.

I mean buy the pl515 osram diode for about 20 bucks. Put it in a module or have someone else do it. Yes the color is independent of the ability to focus it. It is a function of the lens and module. Find someone on here with an LPM. Bribe them or ask them nicely if they will mount the diode in the module and test it on the LPM to get the mA you need to run the diode at for your 5mw. Once you have that number, buy a driver or build one yourself. Put it all together and you have what you need. Is it more expensive? Yup.