Hacking a cheap laser module to get a divergent beam

[luisonoff]

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!

[VDX]

... it's pretty easy to get a divergent beam when insert the laser beam into a glass fibre and then "recollimate" the emitted (divergent) beam from the fiber to the angle you wish

Viktor

[luisonoff]

Hello Viktor, thank you for your tip. Could you explain any further or point me to where can I learn how to "insert the laser beam into a glass fibre"?

[VDX]

... it's simply fixing an optical fiber directly to the diode output or point with the focus on the end of a fiber - the other end wil then emit a perfect round diverging beam.

Look at the images here - I've posted some images with far-field emission of 'naked' 405nm and 445nm diodes and some images with a fiber attached to the diode

http://forums.reprap.org/read.php?27...402#msg-155402


Here is the fiber attached to a 445nm-diode - http://forums.reprap.org/file.php?27...ogen-Faser.jpg

And here the far-field after recollimating with a big lens in roughly 1m distance - http://forums.reprap.org/file.php?27...okus-klein.jpg

Viktor

[luisonoff]

Thank you Viktor. I had no idea about the possibilities of optical fibers, but not so sure it can help me in my project. I mean, I have to mount this on a small RC helicopter, were you suggesting that I put optical fiber inside my laser module before the lens? Or did you mean to replace my laser module for an independent diode plus the optical fiber? In any case I find it hard to place the optical fiber and to attach a lens at its output. What do you think?

[VDX]

... there are optical fibers with different core diameters and made from glass or plastic.

For your problem a plastic fiber with 0.5mm core diameter should be best - length can be from 50mm up, depends on your mechanical setup ... so the diode with battery+driver can be somewhere.

Simply cut the ends with a sharp knife (scalpel or a 3x-shaver blade) and fix one end in the center of the laserdiode window, so most of the emitted light will go through the fiber. For testing I'm embedding the fiber end together with the laserdiode in hot-glue or 2K-glue (with hot-glue the plastic fiber can soften and bend if overheated).

The other end will emit a conical divergent beam - you can try with small lenses, which distance is best for your beam shape and size.

Then put the lens in a piece of tube and fix/glue it on the fiber with the measured optimal distance ...

Viktor

[luisonoff]

Wow, a very interesting option indeed.
The small lens at the end of the fiber should be of what kind or geometry? Is this lens fully needed? I mean, maybe I could get different divergent angles using different diameter fibers? Or will the output angle from the fiber always be too big so I need the lens to narrow it down? I need something like +-5 or +-10 degrees beam.
I am thinking about replacing the laser module with a single laser diode mounted on my pcb, any hints about what diode to choose or where to get them cheap?

Thanks a lot!

[VDX]

... in this image the cone out from a 0.5mm fiber is good visible - http://forums.reprap.org/file.php?27...ogen-Faser.jpg

A 1mm fiber should have a smaller cone, but not so much. But you can try with a tube and a pinhole (1 to 3mm diameter in 5 to 20mm distance to the fiber end) instead of a lens, so only the central part of the beam will emit, the outer part will be absorbed (best tube and inner side of pinhole black).

You can try with any lens you have at hand or can source easily - it's mostly the distance varying with different FL's ...

Viktor

[masterpj]

It must come with a trade off the fiber optic beam correction.
How much did you end up spending for the fiber and correction?

I have 2 445nm modules that I got from a friend as a payment for doing work that also has a very low divergence and a perfectly round beam. Although I bet that one was achieved by using a pin hole. Module is glued shut for airtight seal so I cannot open it.

[VDX]

... I have all sorts of fibers (plastic and glass, from 0.03 to 2mm core diameter) in my scrapery and can give you pieces for the shipping costs ... some lenses too ...

Plastic fibers can be bought for some ten cents per meter ...

Viktor