Help request for replacing a laser diode assembly

[MTWallet]

Re: Help request for replacing a laser diode assem

Thanks for all the help!  I suspected that a loaded scenario might have a lower voltage, which is why I kept pursuing the concept of a dummy load for a green laser.  So I'll get that soldered up and take some test measurements.  Thanks again (To all who have been helping!)

 

[ElektroFreak]

Re: Help request for replacing a laser diode assem

The board that will be driving this module, is it the same as was driving it before? If so, then you should be able to connect it to the diode without too much trouble.. I recommend shorting out any capacitors on the board prior to connecting the laser diode as they can discharge suddenly and kill the diode instantly.

 

[Things]

Re: Help request for replacing a laser diode assem

Just a tip, when you are NOT assembling/taking pics of the crystals, SEAL them inside a bag, preferably with a small amount of silica gel, laser crystals like to suck up moisture, and will reduce your output power very quickly if they gather too much.

 

[MTWallet]

Re: Help request for replacing a laser diode assem

The board that will be driving this module, is it the same as was driving it before?...I recommend shorting out any capacitors on the board prior to connecting the laser diode as they can discharge suddenly and kill the diode instantly.

Yes it is the driver that is built into the mainboard of the mobolazer unit.  I'm not too worried about it not working, I'm just trying to fit all the pieces of information together that have been so graciously provided by you folks here on this forum.  I had read about discharging the cap before attaching the LD, so I had planned on doing that, but thanks for the reminder.  Would I have to do each cap individually, or could I just shunt the + & - pins of the driver output?

 

[MTWallet]

Re: Help request for replacing a laser diode assem

Just a tip, when you are NOT assembling/taking pics of the crystals, SEAL them inside a bag, preferably with a small amount of silica gel, laser crystals like to suck up moisture, and will reduce your output power very quickly if they gather too much.

Wow, interesting tidbid of information! I put the crystal set back into the housing and screwed the endcap back on after the pictures, so I think I'm OK. Once they absorb moisture, can it cook back out from heat generated by the lasing process?

 

[ElektroFreak]

Re: Help request for replacing a laser diode assem

[quote author=ElektroFreak link=1230744297/40#49 date=1232087182]The board that will be driving this module, is it the same as was driving it before?...I recommend shorting out any capacitors on the board prior to connecting the laser diode as they can discharge suddenly and kill the diode instantly.

Yes it is the driver that is built into the mainboard of the mobolazer unit.  I'm not too worried about it not working, I'm just trying to fit all the pieces of information together that have been so graciously provided by you folks here on this forum.  I had read about discharging the cap before attaching the LD, so I had planned on doing that, but thanks for the reminder.  Would I have to do each cap individually, or could I just shunt the + & - pins of the driver output?[/quote]


The absolute safest method would be to short them each out, but you should be able to just shunt the + & - pins.

Also, Nd:YVO[sub]4[/sub] and KTP (the kinds of crystals used in green lasers) are not too hygroscopic. I have yet to have any of my green crystals be adversely affected by moisture during short-term storage. Over the long term, moisture absorption may be more of a concern, but I've never really kept any in storage for more than a week or two.. Other nonlinear crystals like LBO, BBO, and LiNBO[sub]3[/sub] can be much more so, however, and can disintegrate in a matter of hours if left unprotected.

 

[MTWallet]

Re: Help request for replacing a laser diode assem

OK, got the dummy load built tonight and hooked it up to the driver output pins.  As suspected, the voltage dropped when under load, I was getting a consistent reading of 2.4V using three 1N4001 diodes.  However, I'm not sure about the readings I was getting from across the resistor, it measured a 1.4OHM with the DMM, but I am getting a reading of 0.3 on the 200mV setting of the DMM.  Would that mean it is putting out 60mA?  Seems awful small if that is correct.  Just checking to see if my math is right...

 

[ElektroFreak]

Re: Help request for replacing a laser diode assem

Your readings will be skewed a bit by the fact that your dummy-load resistor is not actually 1 ohm. In order to get a truly accurate reading, the resistor needs to be as close to 1 ohm as possible. A 5% tolerance (gold band) resistor should not read nearly as high as 1.4 ohms.

 

[rog8811]

Re: Help request for replacing a laser diode assem

of 0.3 on the 200mV setting of the DMM.

As far as I know that is indicating .3mv, you should not need to multiply up, the meter will read 199.9 at full range. Try using the meter on the next range up, what does it show then?

Just a thought, did you try taking that reading with the power off as well (to see if there is an offset on your meter....which may also explain why a 1ohm reads 1.4ohms as that is way out of tolorence).

Regards rog8811

 

[MTWallet]

Re: Help request for replacing a laser diode assem

Thanks Rog & EF for the replies.  I'll check all of the above tonight again, and also with a different DMM.  If that is truly the output though, sounds like the driver might be trashed?

 

[MTWallet]

Re: Help request for replacing a laser diode assem

5mW of green output usually requires a 200-250mW pump diode. This is due to the fact that the process of generating the green output is 20-30% efficient at best.

Going back to this post, wouldn't 20-30% effeciency of 200mW be 40-60mW?

 

[ElektroFreak]

Re: Help request for replacing a laser diode assem

[quote author=ElektroFreak link=1230744297/0#15 date=1230752324]5mW of green output usually requires a 200-250mW pump diode. This is due to the fact that the process of generating the green output is 20-30% efficient at best.

Going back to this post, wouldn't 20-30% effeciency of 200mW be 40-60mW?[/quote]

That would be correct, but those numbers are only obtainable under the most optimum conditions and with the highest quality crystals and optics.. In a laser like yours, under normal working conditions you'll see 5-10mW of output from 200-250mW.

 

[MTWallet]

Re: Help request for replacing a laser diode assem

...In a laser like yours...

Are you trying to say something about the size of my laser?!?  

But seriously, I rechecked everything tonight, and of course it was me, not the equipment.  When all else fails, go back to the original source.  I was attaching the neg from the driver in between the resistor and the last diode, not on the other side of the resistor (I printed the schematic out in black and white and wrote + and - next to the wrong leads  :-[)  So after hooking it up properly, I get a no load 3.1V which drops to 2.6V with the dummy load attached.  And I am reading 175-180mA with three diodes in the chain.  If I drop to two diodes, the reading goes up to 380mA, but I didn't take a direct voltage reading as that seemed out of whack.  Also, the pot changes current accordingly.  So looks like the driver is good, but I am a little concerned about the direct voltage readings, seems a little high.  But I guess if all IR LD's are in the same basic range of voltage requirements, since this had an IR diode in there to begin with, that the actual loaded voltage once the LD is in the circuit should be OK.

(to see if there is an offset on your meter....which may also explain why a 1ohm reads 1.4ohms as that is way out of tolorence).

I did find that my DMM was reading 0.3-0.4 Ohms with a direct lead connection, so the resistor value is actually 1.0-1.1 Ohms.  Also,  per my story above, would you consider adding polarity markings to your schematics instead of just using color?

 

[ElektroFreak]

Re: Help request for replacing a laser diode assem

380mA with 2 diodes sounds pretty good to me. I'd say that laser's happiest around 250mA +/-. Those readings sound great, so I think you're ready to consider hooking up your diode.. The way most LD drive circuits are designed cause the diode to draw only what voltage it needs, plus you should be able to cut the power back a bit with the pot if you're concerned about it being overpowered.

 

[rog8811]

Re: Help request for replacing a laser diode assem

That seems to be good news all round
Even If I add polarities to my original drawings there are so many copies around, that people copy and post, the chances of getting one with the markings are slim.......You won't make the same mistake again though

Regards rog8811