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Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Hello all, I just got me a used 20watt fiber coupled laser diode on ebay. It is on its way...The seller knows nothing at all about it, but accepts returns. So for 150$ I decided I would see if I got lucky!
So, I need some tips on testing this thing. Its an Opto Power OPC-D020-915-HB/250. There are two left on ebay if interested.
I only have three days to test it and send it back for a refund. (If it is near dead or dead). Now, I dont have a power meter, but Im guessing I could tell if I was getting decent output via the burning of wood, ect. I have been unable to find specs for this thing, but figure most 20watt lasers likely need at least 25amps for full power. My driver can get up to 10amps for short periods of time. (Need better cooling). That ought to be more than enough for threshold, no?
Sams laser faq has one of these lasers on it, but a 3watt version. (DARN!). For those here that know about lasers, what ought I be testing to know if I have a good laser here? Pictures look like it is clean, but from 1997! Wow its old! Could have its entire lifetime used up...
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Hmm, I so wish I was at home right now :-x
I would be very interested to see if it does indeed work, $150 (best offer I assume?) isn't bad even if it isn't 808nm.
In any case, for testing. Due to losses from the fiber coupling process, I am going to assume that there is a 30% fill bar in there which would normally be good for on the order of 30w of power. One way to check is to look at the number of fibers, if there are 19 of them its probably a 20w bar if there are 38 of them its probably a 50w bar.
If it is a 30% fill bar the threshold current should be about 10 amps, and 20w will take about 30a
My measurements show about .5w at 10a, 5w at 15a, 10w at 20a, 15w at 25a, and 20w at 30a. Your could probably be a bit lower and still be good.
Also, be careful about the fiber. If you get dirt on it you can melt the fibers and kid of char them down inside the connector making the diode pretty much useless without cleaving/polishing each of the 19 fiber strands. I find it works well to put a microscope slide cover glass in front of the fiber/diode facet (a mm or two space is enough between the glass/fiber) to keep smoke/etc off of it. You have played with other decent power diodes, you should be able to guess the output power pretty well.
If you are successful I would like to get one or both of them, so keep us posted!
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Yea, the guy doesnt know ANYTHING about them. I asked where he got them from, such as a school maybe. He knows little, or PRETENDS to know little. The returns policy is nice though.
Ouch on the current requirements! I can probably get the current up long enough to test the diode. (I can go past 20amps, but things get nasty hot fast!). The current sense resistors and s shunt resistor I use to measure current with really are what get hot around 5amps. The power fets warm a little bit, but are on a CPU heatsink with fan.
From what I have understood about lasers, as they age, their threshold goes up and efficiency down. So If I push 15 amps through this diode, and cant burn some wood, would it be safe to say its sucking?
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Well, keeping in mind that the output from a fiber coupled bar is extremely poorly culminated (and that power density goes down as a square, so a 1/4" spot from your 2w diodes compared to a 1/2" spot from a fiber coupled bar will be way more powerful then even 6-8w of power) I wouldn't expect to be able to burn wood at 15a. Not without a focusing lens at least. On the other hand, a simple ~1-2cm focal length convex lens would probably focus the laser down to a 1mm or so spot, which would totally etch dark materials. The key would be to use a camera (ir filter or not, there is enough power it will show up) to 'see' the spot, and align everything with ~5a running into the diodes (it probably won't be above threshold, but you will get enough power out to see a spot), then turn up the juice and see if the target starts to smoke.
You could also try doing some quantitative measurements using a makeshift thermal head. Take a piece of black metal (black anodized aluminum would work well) that is as close to a cube as possible (to minimise surface area and thus dissipation), that weighs a few grams. Shine the laser at it for few seconds and measure the temp rise on the block (an IR thermometer would work well for this application, or drill a hole and put in a small thermocouple). Then you can use the the specific heat of aluminum (0.8 J/g*C) to calculate the energy delivered, then divide by time to get power. For example, a 1s shot of 10w would be 10j, which for a 1gm block of Al would be 8degrees C. You could probably calibrate the sensor using your c-mount bars, and get within 20% or so of the actual power.
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Thats pretty slick with the physics! You will do well in college physics. I think I will start with just burn testing with a lens. Then if I am impressed and keep it, ill do more. I do have a 5volt 40amp flatpac that currently provides power for my laser driver. Perhaps I can drop the voltage with some heatsinked resistors. How can I test it for spikes though?
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
Keep a load on the SMPS through some non-inductive carbon resisters. Key after the supply stabilizes, and make sure to >always< disengage the key prior to powering down.
A 20A reversed Schottky barrier diode across the bar is highly recommended.
Most IR diode bars are about 30% efficient. Thus, a 20watt optical output dissipates about 60watts max before warping/frying the bar.
If you did not pay by paypal... they may contact you again in a few weeks insisting the payment was not received... keep the payment receipt.
Any CCD camera should pickup the beam... the 800 to 1080 nm at a fraction of a watt can blind you with even a incident reflection.... try a cardboard box for fun.
Glass may fail to function as predicted in these nm -- need plastic or ZnSe lens. Fiber coupled collimating lens are not cheap...
I must concede I am underwhelmed by the academic background estimate... =(
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
For a quick and dirty driver, how about a SLA battery and a couple of those cement block resistors? I don't see how you can get more spike free than a battery
Or even a length of thin wire might be enough to keep the current down to 25A. I wouldn't use a long coil of wire, though, in case it fried stuff with inductive spikes. Peter might be able to advise on this.
Registered Member #968
Joined: Fri Aug 24 2007, 04:54PM
Location: Norman, Oklahoma
Posts: 104
Twist the power and ground leads together from the battery to reduce inductance. Long/untwisted leads can cause spikes. You probably thought of this already though.
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Carbon_Rod wrote ...
Keep a load on the SMPS through some non-inductive carbon resisters. Key after the supply stabilizes, and make sure to >always< disengage the key prior to powering down.
A 20A reversed Schottky barrier diode across the bar is highly recommended.
Most IR diode bars are about 30% efficient. Thus, a 20watt optical output dissipates about 60watts max before warping/frying the bar.
If you did not pay by paypal... they may contact you again in a few weeks insisting the payment was not received... keep the payment receipt.
Any CCD camera should pickup the beam... the 800 to 1080 nm at a fraction of a watt can blind you with even a incident reflection.... try a cardboard box for fun.
Glass may fail to function as predicted in these nm -- need plastic or ZnSe lens. Fiber coupled culminating lens are not cheap...
I must concede I am underwhelmed by the academic background estimate... =(
Hello, when you say "key", do you mean switch? Like, putting a load resistor in series with a switch across the output of the smps? Then, connect the laser and turn the key such that the load is now open circuit? Also, what is the 20amp diode for? Spikes or accidental reverse voltage?
How much should I load the smps? A couple amps or so? I like the battery idea too, but will want something more permanent. I think I can talk my driver into testing it up to 10amps, and then if it seems to work alright, I will connect it to the smps with 20amps in mind...
BTW- I paid via paypal, so no worries there. Thanks! Matt
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Testing an old 20watt laser diode (fiber coupled)
