First laser module build... failed

[dkumpula]

Do you also measure the Amps while doing this, or just the laser power?
I did the same when I noticed the power dropping.

For visible light, I rarely bother measuring current, although after doing this for over 100 diodes, this should not necessarily be considered a 'best practice'. At a minimum, I probably should at least measure current after I've hit my target output (starting slowly from 0) just to ensure I haven't exceeded the diode maximums. I've read here that some driver pots are 'flaky' so you can't always adjust gain while driving your diodes, but I have not found this to be the case. I just go slow and even slower as I near the top of the power curve. If output starts dropping due to increasing heat / over-driving, I reduce current immediately. I generally settle in around 75-80% of DTR's tested maximums using the same colimating lens. Even less for greens as they tend to be more prone to damage over time.

I can't measure IR accurately over ~808nm, so in these cases I'm forced to measure current in advance and hope for the best.

-David

[VDX]

... I'm building my own diode drivers, as most comercial drivers can't handle fast enough pulsing or create "spikes" when switching them ON or OFF ... attached are two images showing this spikes - the driver was set to 3A (0,4V measured voltage across the shunt resistor) and the spikes goes much more, so will kill the diode pretty fast when running with this transients:




... this is a "good" comercial driver set to 7Amps (0,8 Volts) - the starting overshoot will give a short spike with 9Amps, but this will stay in the "still usable" range for the short exposure time. And you can see the slow deceasing when switching off, so not usable for more than 50kHz pulse rates (I'm pulsing with up to 2MHz!):





... and here is the signal from one of my own older drivers in a high noisy environment - the "noise" is below threshold value, so the diode is off, but the ambient is interfering:






You can see the "overshoot" when switching the power on ... but even more dangerous are the "undershoots" when switching off, as this is more dangerous for the diode than overdriving her for a short time ...

Viktor

[kecked]

that's a really good illustration of what kills diodes. I forget about the reverse voltage but that is certain death. Oh and those long leads act as inductors so they can if large enough create a back emf and blow the diodes. Lasorb helps. It has certain things in it to help with that but I'm not telling you what. Just use them. Don't ask me.

[VDX]

... my solution for short leads is placing the driver nearest possible to the diode or fiber-coupling the diode to get the laserspot to remote positions.

Here a sample with diode+driver - https://vimeo.com/182361375

... and here with a "remote" laser+driver and only the fiber+collimator+focussing head visible (the fiber length is 3 meters) - https://vimeo.com/195822668

The last one is a comercial fiber-laser, but I've built the same type of remote focussing head with fibercoupled IR-diodes too ...

Viktor

[Finale]

Here's two things that only now came to my mind:

1) The mosfet which was attached to the large heatsink which was just laying on my table was not insulated from the heatsink. Could this be the problem?
2) The ground (unused) pin of the laser diode was not insulated and was touching the brass housing which was itself attached to a heatsink laying on my table. Is this an issue too or can I leave my Ground pins as-is?

[dkumpula]

1) The mosfet which was attached to the large heatsink which was just laying on my table was not insulated from the heatsink. Could this be the problem?

Not unless you shorted it out somehow. Just having stuff sitting around unattached is not "best practice" though, so I'd suggest cleaning up your act!

2) The ground (unused) pin of the laser diode was not insulated and was touching the brass housing which was itself attached to a heatsink laying on my table. Is this an issue too or can I leave my Ground pins as-is?

Assuming you meant a case pin, no, that isn't a problem. You just bend those well out of the way of the other pins. It can be touching the diode mount, but doesn't have to be (the diode case itself is mounted within the module, so it is already 'connected'). If instead you meant a ground pin on a case negative diode, that's a different story.

-David