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Registered Member #177
Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214
Steve Conner wrote ...
Unfortunately, working out the maximum power of a laser diode can be a hassle. Some devices "roll over" ie as you continue increasing the current, the optical power starts to go down. For some devices that I've worked with (like semiconductor optical amplifiers), this rollover point corresponds with a sensible maximum rating. But in the majority of laser diodes (afaik) the rollover point can be 5 to 10 times higher than the highest safe current you can use for continuous operation, or doesn't ever happen at all. So by the time you got there, you've already blown it up! :-o
Thats sad. But what about those Lasers from DVDs? You can't get a datasheet from them, so I guess using, say constant 40mA on them would be safe no?
Registered Member #119
Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114
I might try cannibalizing some old modules. They were fairly nice modules, so I'd still like to try to repair them, especially since it is good experience. What would one search for on Ebay to find broken green laser pointers? I tried things like 'green laser parts' and 'green laser broken' but couldn't find any models being sold as broken.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
they don't turn up too often, but searching for 'dpss' 'ktp' 'nd:yvo4' 'vandate' 'yag' 'nd:yag' etc seem to turn up the kind of stuff. I don't look too hard for them, but in the past year or so I have seen 4 auctions, one that was for a 100mw lab laser missing the crystals, one for a single vandate/ktp from a laser pointer, the one I got for a bunch of parts, and a lab blue laser that went for way more than it should have.
Since you already have a pretty decent stockpile of them... I would suggest pulling the diodes (that is probably what is fried) and looking for some .5-1w ones. If you can leave the crystals/lenses attached as they are tricky to align properly (without perfect alignment between the diode/vandate/ktp you won't get any light out, when all you need to do is align the diode it is much easier), and you might damage the crystals getting them out of the mounts. Be very careful not to scratch them, as the coatings on them are very delicate.
If you get diodes in a can you will need to find a focusing lens to focus the light from the diode onto the extremely small spot needed for lasing action, or (very carefully) dremel off the can and hold the vandate directly up to the laser diode (the active region of a diode is about right for pumping vandate). I wouldn't recommend buying a bare diode chip as it will be a major pita to mount it, but if you get a decent deal on a chip in a c-mount I would go for it (but be absolutely sure it is a single emitter, most high power diodes are a bunch of smaller diodes attached to one another).
If you get really fed up with the crystals... I have a small composite crystal that is like 1mmx1mmx3mm (or something, I haven't looked at it in a long time) that I would sell/trade pretty cheap. But really the best way to get into these things is to buy a working pointer (they are pretty damn cheap these days), as you have a real laser diode driver, a known good diode, and complete set of crystals, and a correctly matched set of beam shaping optis.
Registered Member #119
Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114
Here is a small web page I just made to give an overview of them: It has various pictures of them that might help in the discussion. Assuming I can keep the optics on their respective parts, keeping everything aligned shouldn't be too bad since they will be aligned by some screws. Of course, I'll have to be a little nicer to the Nd:YVO4 next time. Here is a picture of the diode: Can anyone estimate how powerful of a diode that is just by looking at it or should I just stick to looking for .5 to 1W diodes? If anyone has any, feel free to PM me with what you have and what you want for them. The Nd:YVO4 is 4 X 3 X 1mm. Will there be any ill effects by using a smaller crystal? I forgot to mention, if I recall, I can see a bit of red light coming out of the other two "dead" laser modules, but it is VERY dim. Does this mean the laser is very near dim, or something else? I was under the impression that nothing should really cause any red light to come out. There was a hint of green in it as well. I still need to figure out a way to get the epoxy off of the nuts to dissasemble the other lasers. I haven't been able to look at them because I can't get the actual laser assembly apart. Guess I'll have to just patiently chip away at it. Once again, thanks for the help.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
The dim red light is the 808nm light from the pump diode, this means one of two things... Either the laser got knocked out of alignment (not likely) or the laser had been damaged and is now either emitting incoherent light, or too little light to produce light out. The little green you are seeing is from the few photons that do make it through the thing...
Also, looking at that thing you have a pretty powerful module, and the mount the laser is on looks a lot like a normal C-mount. www.roithner-laser.com is the only place I know of to get new laser diodes...
They want $46 for a .5W 808diode on a c-block (p/n LDM-0808-500m-12) , or $127 for a 1w one (p/n L081T1a). I would go with the 500mw ones, you should be able to get 50mw out of it They are actually really god for pumping micro crystals, with their 50um stripe width
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
Steve Conner I must say I am impressed... Personally I only built a few of my own drivers a few years back. And have had mixed success even with the cheap generic driver units they now sell. Here is a classic example of a simple test driver (Sorry but I can’t recall where its from and doubt it will even work with newer laser diodes – just thought it may be interesting.)
Cheers,
Shhhh, nobody point out how my transistors arrow looks like it points backwards on higher resolution screens. ::)
Registered Member #119
Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114
I found some references to the power for my lasers. The green one can be found here under PGL-I-S and PGL-I-R: It says they are suppose to operatate off of 5V. I also found the red module that I mentioned earlier(or something like it anyway) and it said it should also be operated off of 5V. I had forgot that one of the modules was an IR module, and not actually broken. I put the broken Nd:YVO4/KTP in front of it and it glowed green. So, I'm up to 2 or so working modules. I suppose I could try to swap out the working Nd:YVO4/KTP from the other broken green laser and put it into the IR laser if I wanted to get 2 green lasers working. That price list was very helpful. I'll look into getting a new laser diode from that. Even if I don't, I found it very interesting to look through.
Registered Member #87
Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191
I won't mention how the arrow on your transistor looks backwards on higher resolution screens, but I wiil point out that the decimal between the 1 and the 3 has morphed into the three, making it apear as if the circuit calls for a 135 volt battery..
Registered Member #119
Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114
Ha, I was wondering about that 135V. Why would you have a 1.35V source? That sounds like a really odd number of volts, or is a "1.5V" battery really 1.35 and I'm just forgetting? Also, I am having a bit of trouble understanding this cicruit. From what I see, the base/emitter voltage going to the laser would just end up at 1.35V potential again, so there would be no potential difference across the area with the laser. What am I missing?
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Green Laser Repair
They are actually really god for pumping micro crystals, with their 50um stripe width 
