laser diode

[zoltan]

Hi,

I got a laser diode of 50W, 805-810 nm. I did not try it but I was thinking about a laser head for my cnc machine. It has a short fiber coupler and I hope to get a lens for it. I bought a fluid cooler for computer microprocessor I plan to use it for cooling, and I found out an old computer power supply of 3.3 V that I hope to be able to modify for it. Is here somebody did something similar with a laser diode or do you have any ideas how to build it? The first issue is how to control the current of the power supply in the range of 18-45 A with 5V TTL signal? Also, I must modify the power supply as I think it delivers now only 15A. The second issue is how to focus the laser beam? I mean a mechanical construction for it.

Any ideas?

Thank you.

Zoltan

[MacGyver]

That would make for a nice YAG-style cutter. If you don't know what you're doing, do not try to modify a computer supply... purchase a purpose-made supply for the laser. Diode lasers aren't very forgiving when it comes to power, and you could easily fry the little bugger in an instant. BTW, 15A is fine for 50W.

You focus the laser beam the same way as any other beam, with optics.

[zoltan]

Hi,

First of all, thank you very much for reply. I really appreciate it. Could you, please, give me more details about how do you think I should make the cutter? What do you think about optics assembly, how to construct it? Did you made something like this?

Thank you.

Best regards,


Zoltan

[maxbela]

I would be interested to know how to put together a laser marking/engraving/cutting head to mount on my CNC router set-up. Has anyone done this successfully?
Sources for the parts required would also be a help.
Thanks in advance for any help that can be offered.
Max

[MacGyver]

zoltan, If the diode assembly is small enough, you could simply mount it on the flying head and directly attach the optics. If not, you'll have to use several beam-bending mirrors similar to a standard laser table setup (look at pictures of existing tables to get an idea of how everything is pieced together). There are also plenty of threads on the basic idea behind constructing a table, so do a little searching.


maxbela, your success would depdnd on the quality of your table. CNC machines are typically built to handle/move heavy routers, but their accuracy and/or repeatability may suffer, which will have a direct effect on the quality of any laser work. You have the basics already, including X/Y positioning as well as a router on/off or Z signal to use for turning the laser on/off. All you need are the appropriate optics.

[maxbela]

Thanks MacGyver,
I think my table will be OK, I have not detected any loss of steps even when milling thick alloy blocks. Repeatability is quoted as 0.02mm (0.0008 inch) by the manufacturer.
Presumably under no load since there must be some distortion of the framework if it is under a heavy load.
It is the laser end of things I am not clued up on. I have used a commercial CO2 laser engraver on many materials in the past but, due to the huge cost of that machine, I thought I would never be able to get my own so I did not take the trouble to go into the details of all the different types of laser and how they work.
I shall be searching around to gain some education!
Cheers
Max

[zoltan]

Hi,

Thank you very much. The diode is small about 6cmX4cmX1.5cm and it has a blue cap (fiber coupler I was told) of 4mm and 10 mm long. I will make tomorrow a picture and post it here. I bought it on eBay together with a collimator, but unfortunately, it seems that the seller forgot to put the collimator in the parcel, anyway he promised me to send it to me by tomorrow. So, actually, including the cooling system the size of "laser head" is 12cmX12cmX10cm which is making it a nice candidate for flying head. The problem is that I do not know what kind of lens I need as I am not sure if the collimator is OK. I am referring to the coating of leans, focal length, distance between the fiber coupler (the blue head/cap) and the lens, etc. That is my issue. I was told that a capacitor of 10 microF is needed on the legs of diode in order to avoid the electrostatic damage.

Please, I need as many as possible advices.

Thank you.

Zoltan

[MacGyver]

zoltan, Parallel capacitors don't prevent ESD, but a series resistor will... a parallel cap is used to avoid voltage spikes coming from the power supply, kind of a soft-start circuit. I will repeat my earlier comment of not skimping in the power supply department. Be extremely careful about using switchers as any voltage spikes that can leak onto the output can kill the diode in short order.

Since you're dealing in the 800nm range, you actually have a wide range of optics open to you. Starting from cheapest to most expensive (roughly), you have: BK7, UV Fused Cilica, CaF2, and MgF2, all of which have 90%+ transmission factors, as well as SF11, Ge, and ZnSe, all of which have much lower transmission factors (around 60%+). If you plan on using the same system with a CO2 laser sometime down the road, I suggest going with the ZnSe for compatibility.

Focal length will depend on what you're trying to do with it. For cutting, I would go with a longer FL, somewhere between 4-6", for engraving something in the 2-3" range might be more appropriate.

Once you add on the cooling system, power leads, etc. that chunk may become a bit heavy to fly around at high speed without some beefy motors. I would suggest simply running a fiber to the flying head, that way the motors can remain small.

I can't say what kind of cutting power you're going to get from 50W at that wavelength, but I know other similar systems exist. I'm even aware of a 1W system that's being used for micromachining (MEMS). If you don't mind my asking, how much did you pay for the block?

[zoltan]

Hi,

Thank you again. I have bought it for $460 from ebay as I said together with a collimator. You can see in attached pictures the diode and the collimator as they have been advertised on ebay. Unfortunately, the seller forgot the collimator but he promised me to send it, and I really hope he will keep his promised as in Romania is difficult to find out such a optics.


Zoltan