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Testing an old 20watt laser diode (fiber coupled)

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Carbon_Rod

Fri Oct 03 2008, 02:34AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Thank you Steve, Dragon NaturallySpeaking can't tell the custom word dictionaries apart very well.
memorandum mori =P

Matt, always keep the SMPS output under a minimum 3A load (kept it stable for the one I tested.) And yes, some bars will be damaged by a slight reverse voltage.

EEYORE

Fri Oct 03 2008, 03:59AM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Carbon_Rod wrote ...

Thank you Steve, Dragon NaturallySpeaking can't tell the custom word dictionaries apart very well.
memorandum mori =P

Matt, always keep the SMPS output under a minimum 3A load (kept it stable for the one I tested.) And yes, some bars will be damaged by a slight reverse voltage.

Hello,
So would that be a yes to my idea with the SMPS and the resistor switch algorithm?
1-Connect everything together with power off. (SMPS, load resistor and reverse voltage diode, laser diode).
2-Connect load resistor across output of SMPS via switch.
3-Turn on power.
4-Wait a few seconds, and then disconnect the resistor via switch.
5-Connect resistor via switch.
6-Power down.

Also, as far as testing the setup before connecting the laser goes, I was thinking about buying some cheapo laser diodes and sacraficing a few to see if the "kinks" are worked out. Seems to me, that those little laser diodes are much more sensitive than these power laser diodes. See anything wrong with this idea aside from wastefulness and ill will for the laser diodes?

Thanks,
Matt

Carbon_Rod

Fri Oct 03 2008, 06:22AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
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Posts: 1155

1. Allow supply to turn on and stabilize (leave the 3A load)
2. Switch "on" laser diode through series resister (50watt at a few ohm should be fine.)
3. Switch "off"
4. Turn off power supply

* Keep the laser power wires short (or you will get drift)
* use a DC clamp-on ammeter (normal probes will mess up the characterization)
* start at 3A for the laser, and seriously monitor the voltage across the bar
* the SMPS will need a mod for adjusting the outputs down
* use a power MOSFET with low rds ON for your key (no arcing)

* a battery is unregulated (keep it for the dollar lasers)

* ceramic blocks will not be good for this project (spend the $20 to get a few r values to build a characterization ladder board)

* sams FAQ about the wire resister is not good practice, but IIRC he does mention a server SMPS retrofit on the site someplace

* Don't try anything without the protection diode across the terminals of the laser
(Often a 30A relay running off another supply keeps the laser shorted when not in use)

* I have tested the older modified Dell SMPS for continuous operation at 20A

EEYORE

Fri Oct 03 2008, 05:56PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Got the laser today and I am horribly shocked at what I found. A laser just SITTING in a box with no padding! The case of the laser is missing ALL its screws and dust COVERS the optics on the inside! The power pins are destroyed on the outside! DO NOT buy ANYTHING from these people! I am awaiting an RMA number so I can return it, and will be contacting paypal asap.

Ive never seen anything like this in my life! Geeze....
So now I will turn my focus to one of these lasers:

Looks much better, but after my recent episode, I will bid rather than buy it now. 200$ is alot for a laser in unknown condition.

Matt

Carbon_Rod

Sat Oct 04 2008, 12:27AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

The RMA is an e-bay delay scam, as IIRC after 30 days paypal will ignore you and the guy keeps the money.

File a refund request with Paypal now, and include the tracked shipping number for the return.

Also, file a $50 e-bay Safe Harbor case if the seller gets mad and refuses to refund.

Good luck,

EEYORE

Sat Oct 04 2008, 06:46PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

No worries, the seller refunded me once I sent him the tracking to show it was on its way...

Now I bought a new one:

So the project is back up!

Its a 40watt laser, made in 2006. Looks clean, and has a shorting wire on the inputs. Also, seller gives me a 30 day guarantee it will work. (Ive done business with him before, and returned some things successfully). Only drawback is that it doesnt have the fiber cable. I have no idea where to find one of those, as the part number on the coherent site says its an 810um diameter core! Huge! (Well, relatively). Is the cable all that neccesary for this diode? Could I just use a simple lens to focus the light (and protect the fiber bundles inside the termination)? Or, do I really need to get ahold of a fiber cable? He had a few others up, but all but one is gone now. (I got the cleanest looking, youngest one!)

Thanks!
Matt

...

Sat Oct 04 2008, 07:29PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I have a few fibers, and yes it is a .8mm core. And yes, they are a pain in the butt to focus ;) And yes they are super expensive...

They will turn on up ebay once in a while for about $50-100 for a 5m or so cable (I don't know why they don't come shorter than that). The best thing I think you can do with them is cut the fiber in half, strip off the kevlar, cleave the end, and use it for burning. If you managed to destroy it (they snap pretty easily, especially right at the connector end >.<) When that end gets trashed, cleave it again and voila. No focusing lens needed (40w over a 1mm spot is a fair amount of power). If you are feeling adventurous, you can leave the cable in tact and use a microscope eyepiece lens to focus it, I managed to get something like a .3mm spot at a cm or two away with a 20x microscope eyepiece lens.

But in the mean time, yeah you cah use the beam strait out of the laser, although I would unscrew the coupler first. You can probably use a normal magnifying lens to focus it, just make sure to not get smoke on the lens or especially the laser!

EEYORE

Sat Oct 04 2008, 07:39PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Ok, so I can play around with the laser some before trying to locate a fiber cable...I wonder if I could rig up some kind of lens to the actual termination. Any idea what that is? SMC, ect. I have an AR coated collimating lens that ought to focus the laser down a bit if I could somehow reliably stick it on the end of that termination. I wont be able to get near 40watts, as I just have a 40amp flatpac, but that ought to be enough for some fun. At least 20watts...

Keep fingers crossed, $200.00 is an awsome deal for that laser if it is good, no? I have a feeling it was pulled for a reason.

Well see...According the the power vs current graphs on the coherent site, 15amps ought to do 10watts, so if I crank it up to 15amps and get pitiful output I will return it...
Matt

...

Sat Oct 04 2008, 08:17PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

It is a SMA-904 connector, the threads are the same as a normal SMA rf connector (if fact a good hack to make a coupler if you are missing one is to use a take a female/female sma bulkhead fitting and press out the plastic dialectic/center conductor).

You could probably put a lens on the output of the coupler, although I worry that you will run into problems with the beam hitting the sides off the coupler. The raw output of the fiber is will look more like a flashlight than a laser beam.

EEYORE

Sat Oct 04 2008, 10:06PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Hmmm
maybe radioshack has some connectors. I do have a 2.4 watt fiber coupled laser that I can try some fittings on. At 20 watts, this will have to be a very close fit, eh? What are your thoughts on back reflections?
Back to power supply: Is it healthy to hit the laser at 30 amps at turn on? Should a soft start of sorts be used?
EDIT: Alright, so I pulled up a data sheet on the vicor flatpac's.

Mine is the VI-LU0-EU. What should I be looking for in the specs as far as stability goes for a laser? So far, two things stood out to me; Load/line regulation: Max=(VNOM LL to HL, 10% to Full Load)=0.5%/ (VNOM LL to HL, No Load to full load)=1.0%

AND Output Ripple = 250mV (p-p 20 MHz bandwidth).
To tell the truth, I dont know if these are good or bad, but 250mV seems to be alot, no?
I dont know the resistance of the laser diode, but know its supposed to drop like 2 volts. So would it be safe to say: 5v-2v=3v/R to figure the current limit for the laser?
matt

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