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Mystery C mount laser

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LAN_403

EEYORE

Mon Jun 02 2008, 06:00PM

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

Hello all,
I recently bought a couple C mount laser diodes. I dont know anything about them except that they are IR, and likely made by Coherent. From observation, the laser chip has 6 bonding wires. From experimenting, 3amps seemed to have killed one...They deffinately burn things, unfocused...
I would like to find out more about them, but they dont have any markings that show up on a search.
Does anyone here have any good experience with laser diodes? I cant seem to find any good answers from google...One is, what is significant about 6 bonding wires? On some, the laser chip is red when lasing, and on others it is blue. (Actual laser output is invisible except on camera). What does this tell me? I hacked apart a cheapo laser pointer for its lens, and held in front of the laser output of one of the mystery lasers. It collimated the beam and burnt lots of random stuff...The lens/holder got very hot! My guess is from the lens not being AR coated for IR?

So here are the questions summed up:
1-What is important about 6 bonding wires over say, 5?
2-What does a red glow over a blue glow tell me?(Laser chip itself, not actual laser radiation).
3-How to estimate power output? (Never will have money for a power meter)
4-Where can I get optics to collimate the laser?
5-When heatsinking, is it proper to mount it like a transistor?(Standard heatsinking compound)

If anyone here has experience, and can tell accurately test them, I will send one for free to you and you keep it when done. How about that?
Thanks!
Matt

...

Mon Jun 02 2008, 06:25PM

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

Ok, before you continue testing you need to find some laser saftey gear. These chips are possibly putting out several watts of power, and without a decent set of goggles you are flirting with serious eye damage.

1. The 6 bonding wires means that the diodes are good for a bit of power, although it doesn't give a definitive amount of current that it is good for. I would estimate that it is indeed good for a few amps, although it depends on the size of the wire, duty cycle, how over designed the laser is, etc.

2. The diodes that glow red are mid-IR, possible 808nm but more likely somewhere around 780. The ones that glow blue are probably a far IR diode, probably 1.5um. Although its is hard to say without hooking it up to a spectrometer...

3. Estimating the power output is tricky, but generally you can assume you are getting about 30% efficiency--so if you are running at 2A ans 2V (4w input power) that is a little over 1W of output power.

4. You can probably find the optics on ebay, although high quality optics for this stuff is pretty expensive. You might have better luck using the lenses out of a dvd-rom (or preferably a fast dvd-r drive) since they will at least be AR coated for mid-IR radiation. The far IR diodes would really benefit from some real glass lenses, or even possibly ZnSe or the likes depending on how far IR they are.

5. To heatsink then you just bolt them down to a block of copper. IIRC you should use a 4-40 socket head cap screw, with a flat washer. I am not sure on the correct mounting torque, but I would tighten it about as much as can without risking stripping the screw. BTW, make sure that you countersink the hole in the heat sink you are mounting it to or else it will deform the copper when you tighten it and reduce heat transfer a little. I THIN layer of heatsink compound is a good idea, although indium foil is generally preferable.

I would love to test one of your diodes, and I have some good coldplates and a decent power meter that I could use to do power testing. I don't have a spectrometer on hand, but I could probably convince my boss at work to let me shine it at one of theirs to get the wavelength on it.

Cheers

EEYORE

Mon Jun 02 2008, 06:49PM

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

Hello,
PM with your address and I will send one out to you.
Matt

EEYORE

Sun Jun 08 2008, 10:15PM

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

Alright, so I have played with the lasers and killed a couple...Now it is time to mount them such that they are safe from contamination. (Smoke from burned objects keeps getting on the laser chip face). My idea is to mount the laser on a 2in brass disk (1/4in thick). And then mount this in a rugged aluminum project box. I am still working out how I will focus the laser...It is highly divergent...
Should I go with a GRIN lens to reduce the divergence and then shine the output into an AR coated collimating lens? Or Should I attempt to find a collimating lens with super short focal lenght? I am going for max power out, so the less glass the better. Plus, GRIN lens are about $25.00 plus shipping...My power supply is a battery pack. (2-4500mAh NiMH batteries, with about 0.16ohms in series). This gives me a measured 2.1A through the diode. I ran them past 3amps, but they get hot fairly quickly like that, and one failed. (I assume from heat, as the heatsink was pretty toasty). So I will keep them around 2A....Im guessing this is a little over 1watt of laser power...
What do you guys think?
Matt

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