My new DIY red laser

[alessnilsen]

Hello! I recently bought five DVD burners to play, I know that this devices have a low power laser (infrared?) and a high power laser.

I disassembled the burners, two have a open can type LD, one has a frame type LD, one has a dead LD ( :cryyy: ) and the last have a closed can diode .

I used to have a chinese 5mW green laser pointer, it dead, so, I reused the module, the closed can LD fits well into the module, but not perfect to allow a perfect cooling.

I assembled a driver to the LD using LM337 amd a li-ion 7,4V battery, I don't know how powerfull it is, I started with 140mA, I increased up to 200mA and the laser output was stable, but the LD was getting too hot, I decrease the current to 180mA, but the resistor of the driver was getting too hot, so, I decided to keep the current of 140mA and everything was fine.

Since my green laser had broken lens, I used the collimating lens of the DVD burner and glued using cyanoacrylate glue, since the collimating lens is pretty big, the beam diameter was around 4mm.

About the other lasers, my driver killed all , I was using a trimpot to set the maximum current, the trimpot gets hot and more hot, increasing the current without my permission!!!

Some pictures:

 

[Blaster]

Not a bad project you have gone to quite a bit of detail to explain your findings .i found it quite an
interesting read and some good pixs as well.

 

[alessnilsen]

Thanks! :yh:

This LD I got from a 8x DVD burner, model LG GSA-H12N (can someone confirm this?), how much current I can put without damaging the LD? Any idea to increase the cooling of the LD?

I'll put this laser into a case, to be more fashionable.

Also, I don't knew I can control the output power of a laser only controling the supplied current

 

[SKeeZ]

Love the aesthetics! great job though +1

 

[Blaster]

Yeah on aesthetics oh and + 1 ,more like real laser stuff i tend to just want to buy everything in sight, not sure on the current if i new the output power could reverse engineer and come close to the input current required ..i think those burners are about 250mW ..think don't know for sure im sure another forum member will know what power a DVD burner outputs and hence the current

 

[alessnilsen]

Thanks!

On the first post I said that one of the LD's was dead. Isn't! It's a frame type LD, I'll keep it on the original housing, and attach it on a heatsink. Is from a Lite-On DH-20A4P, maybe a 20X burner? :wave:

 

[Flaminpyro]

Way to go, this is how we learn by experimenting, thanks for sharing, +4

 

[alessnilsen]

Thanks!

Now I'm projecting a osciloscope (will display perfectly the waveform of a music) with this second LD.

But I must determine what lens I will use and the max current to the LD, I need collimate the beam and mirror it to the osciloscope, I can do this using the mirrors and the beam splitters that I got from the burners.

Soon I will post some pics!

 

[The Lightning Stalker]

Any idea to increase the cooling of the LD?

For good cooling, the diode has to be clamped tightly into the heatsink. Most modules such as the AixiZ are press fit. Some are threaded and can be tightened with a tool. I can't tell which type yours is from the pictures. The material the module is made of also makes a difference. Most are brass and that is what it looks like yours is. Aluminum would be slightly better and is actually cheaper, but I haven't seen any made from that. Copper is the best, but also costs the most.

 

[alessnilsen]

Unfortunatelly, the LD cannot fit correctly into the module, so, nothing I can do.

I have more two questions:

1° When I use the laser diode without a collimating lens, it puts out a big blur of light, when I put a lens, part of this blur is collimated and part is lost, how I can collimate all the output of the laser? I think doing this will make all the output of the laser diode be better utilized.

2° I'm using a LM337 as current regulator, but I'm getting erratic readings from my multimeter. For example, with a voltage of 7,4V and using a 5 Ohms resistor, must give me 250mA of current, but when I read the current with my multimeter, the measured current was 211mA. Using the same voltage, but with a 10 Ohms resistor, must give me 150mA, but the measured current was 185mA. When I remove the multimeter from the circuit, the current increases substantially. Any idea of what is doing this?

Some pictures of my other LD.

 

[The Lightning Stalker]

To answer your first question, the two solutions are to either move the lens closer to the diode, or to use
a bigger lens. The lens in the pictures looks like the bi-concave lenses found in some DVD drives. That
one has a pretty long focal length and does not make a particularly good collimating lens. What you
need is a plano-convex lens. I've heard of using the objective as a collimator, but it's pretty small and
you might run into the same problem. It has to be pretty close to the diode as well. The easiest option
is to use a coated AixiZ style lens, that is if you can afford one.

 

[alessnilsen]

Move the lens close to the diode didn't help. Using the objective lens as collimator give me the best result! A laser that burn things very well! The only strange thing is that this lens create various circles on the collimated beam!

This laser burn things very well @ 235mA! I think I can get more power from it.

I'll get one more DVD burner to extract the objective lens mechanism, I will have a electric control of the focus.

 

[The Lightning Stalker]

The focal length on that bi-concave is just too long. That and it's the wrong kind of lens in the first place. The rings could be from not having an aperture around the lens. I'm not too sure. I don't know a whole heck of a lot about optics.

 

[alessnilsen]

The objective lens isn't biconcave, is a plane-convex lens. The other lens I used, is a concavo-convex lens.

My LD is dead

I need a driver to use with any voltage, stable and reliable. Since my circuit with LM337 killed my last LD (because the current increases with the tension), I don't want spent more and more LD's.

I was thinking in a driver that uses a 7805 or any other regulator as constant current source, any idea?

 

[Cube777]

Did you use the LM317 as a voltage regulator or a current regulator? The sporadic current readings can be caused if you used the LM317 as a voltage regulator as the LD's resistance changes according to its temperature (thus causing different voltage readings and weird current readings if you only had a constant voltage source). To use it as a current regulator you can use the circuit on THIS thread, also using a LM317 but in constant current mode. Hope this helps. Nice build BTW!

EDIT: Will someone please correct me if I am wrong, but if you used a LM337 the same rules should apply as mentioned above.

 

[djQUAN]

Which one exactly did you use? LM337 is a negative regulator. LM317 is the positive version.