Laser diode lifetime

[Buriedcode]

I've seen these  extremely cheap red 5mW (advertised, not measured) laser "modules" all over ebay and aliexpress - bought a few just out of curiosity.

They appear to be this type:
https://hackaday.io/project/12889-mid-air-laser-image-display/log/43441-cheap-laser-diode-module-teardown

After checking alignment, the ones I have seen pretty good, so I was going to make a bunch of alignment lasers using these - just a tube with a single cell AA/AAA, and driving electronics.  But looking at that teardown it appears its just the bare diode - apparently it isn't even encapsulated - and a single resistor, the value of which is changed for 5v versions compared to the 3v I have.

I'm aware these are engineered down to be the absolute cheapest, and there are much "better" modules available fairly cheap - but I was wondering if one could increase the life of these - I'm assuming they really don't last long - with a half decent CC driver?  I'm including a single cell boost converter anyway, so I might as well drive the diode properly and not waste any power on that current limiting resistor.

It doesn't appear to have a built-in PD for any feedback, which is why I'm assuming that the life of these isn't going to be great, but as I'm making a driver, I could at least try to drive these a bit "better" so I don't have to regularly swap out the modules.  Is it as simple as constant current, perhaps driving at 80% of what its currently getting?

Perhaps I should run a test on these and see how long they last when powered by 3V.

[ajb]

It doesn't appear to have a built-in PD for any feedback, which is why I'm assuming that the life of these isn't going to be great

Ehh, the use of a photodiode for feedback isn't the least bit critical for many applications.  It's most important when you either need closed loop control of actual (precise) laser power or feedback as to whether the diode is operating or not.  The only impact a PD might have on lifespan is if you're running the diode near its maximum optical power, in which case the PD feedback may help you stay safely below that.  Laser diodes are very unforgiving of exceeding their max optical power -- in any laser operating normally, the power density in the cavity is VASTLY higher than the power density in the output beam, and in a direct injection diode like this that tiny little semiconductor sliver IS the entire optical cavity, so very easy to get a hotspot and then a cascading failure.

So that's really the most important factor in lifespan: never ever exceed the maximum rated optical power, even for a moment.  Since you're talking about making your own driver, and a switch mode one at that, you need to be very careful to avoid any overshoot or other instability in the driver output.  Even a very brief overshoot can cause a small amount of damage that will accumulate.  Reducing the operating power doesn't hurt either, less power is always less stressful and it means more headroom for whatever overshoot you do end up getting.  But if you don't know what the actual ratings of the diode are, then you can't really quantify that: reducing the power to 80% isn't a huge help if the original power level was 150% of the rating!  Setting the power to the minimum that works for your application is about the best you can do there.  Of course ESD is also a concern like with any semiconductor. 

All that said, laser diodes like these are a pretty mature technology, and you might not have any problem at all with their longevity just because they're cheap.  Of course if you need something with a reliable lifespan, then there are better options.

But looking at that teardown it appears its just the bare diode - apparently it isn't even encapsulated

That's pretty similar construction to what you'll see in most individually packaged laser diodes.  The die is the entire laser, so you can't really "encapsulate" it like you would an IC or even an LED because the faces of the die are the cavity reflectors.  The most you can do is put it inside a hermetically sealed can, the inside of which would look fairly similar: just a little sliver of InGaAN or whatever stuck to a chunk of brass with a single bondwire on top. 

[Buriedcode]

Thanks for the detailed reply.

I'll test some of these with a CC power supply - I have a small one I made for testing LED's that slowly ramps output up/down, and has voltage clamps - to see what kind of brigthness is acceptable. As they're already pretty damn bright I think I can get away with going a fair bit lower.  And I have quite a few so if I kill a couple in testing it doesn't really matter.

[Terry Bites]

I got a bumper bag of these diodes, hours of fun. Fewer cats crapping in my the garden and the evil squirrels are assuming the position.

I've been running them on full current at a low duty cycle to keep the power drain and self heating down to a minimum.
I can't tell the difference in brightness on 100% vs 5% (optical integration and such) and they're doing great after 5 years of service.

I went mad and used a 2Rs, 2Cs a 1N914, a 4093 and a BC107! Later I made a long MS ratio Osc with an SN74AHCT1G14 and a tiny mosfet.
You might even ditch the transistor

[Kleinstein]

The newer laser diodes tend to be less picky about the current and can get away with a simple current source / resistor. The photdiode feedback was needed with the early types as the threshold was relatively high. So a fixed current could be to low and thus no laser acteion when warm and still too high when cold and damage the laser from too much power. Some of the laser diodes get damaged from too much optical power, not just to much overall temperature.

Another important part with laserdiodes is ESD protection. Adding good protection would be a first to get a longer life.