8X Diode Murder fund

[IgorT]

A bit off topic...
I recently built a pointer for someone with an SF-AW diode. At 155mA, the yellow halo was very noticeable. I have never seen this with PHRs or GGWs, so I was a bit intrigued. I thought it may be fluorescence from something in the module, but I could not find any possible source other than the die.
I didn't notice it with an Aixiz 405 lens but it was clearly visible with the 405-G-1. Maybe I just wasn't looking hard enough?
Hopefully the yellow halo is not a "bad" thing.

I first started noticing it a year and a half ago, when i had a bad eye infection, couldn't wear lenses and had to wear my glasses, which block 405nm quite a bit.

I was also intrigued, cos i thought it was a new thing, but it was the glasses that allowed me to see it. Usually it is obstructed by the 405nm glare.


Later i started noticing it even more often when shining various diodes through my wavelength sorting filter. It would block most 405nm, and pass the "yellow halo" so it was very noticable there.

It really scared me at first! For a while i was weeding diodes with it out from the rest, but then i realized it is too wide spread. Barelly any diode was completelly without.


Then i started writing it down next to PIV data with each test (the presence and intensity), to see if those diodes would die sooner, but it never happened. I was unable to find any correlation between yellow halo presence/intensity and diode lifetime.


Most 405nm diodes have it in widelly varying intensities, but without a filter or protection glasses it is hard to see due to the intensity of the spot.

The reason you only noticed it with the 405-G-1 is that your diode must have a stronger halo than most, and that short FL lenses like the 405-G-1 increase the size of side projections, making it come out from behind the glare.


I wouldn't worry about it.

Only thing i haven't seen before is the halo changing in intensity, which is why i'm paying more attention to this 8x now, to see if it's really changing, or if i just happened to notice it now, and not during earlier tests by accident....

If it is actually changing, it could be a further indication of degradation in this case.

The number 3 plot looks like a copy of the #1 plot, scaled out in time 5x... unless it's just a coincidence of measurement error, it looks as though the #1 diode is degrading at 5x the speed, but the same pattern.

The curves do indeed show striking similarities, and you can be sure, i considered all sorts of possible errors, and eliminated them one by one, when i saw that power is suddenly higher with both diodes.


When i turn off the cycler, i wait for diodes to cool off, then i attach them to the diode analyzer, and warm them back up a bit, till they are exactly where they were during the previous plot. I use Vf for confirmation, that the temperature of the diode itself actually matches the previous testing, and don't allow more than 0.01mV of difference before making the next plot.


I don't know why or how, but it seems that powers of both diodes did actually go up a bit once or twice!



However, the graphs are similar, but not quite copies. The differences could be the result of different diode "toughness"...


We'll know more in a bit, only 30 cycles to go till 140 and 280 hours!

 

[IgorT]

No .
One thing ,i'd like to mention, is that ive noticed is that around this current (460mA) the 8x seems to bo "topping off" as far as power output.

What do you mean by "topping off"? Did you plot it and found a knee (or more likelly a kink) there?

So i changed out my dead 8x , into a 12x , i just exchanged out the diodes.. its shooting out 640mw . i would have thought the 12x would have been putting out much more than the 8x.

i do have to say that in the minute on , minute off tests , it doesnt get as warm as the 8x did

So you left the driver at the same current, only switched the diode and got the same power?

If you're sure it does not get as warm, it would mean that the diode has a higher efficiency, and since the current and power are the same, it can only be a lower forward voltage. Altho that would be strange, as 12x's show a higher Vf than 8x's, altho they do vary quite a bit.


Otherwise, some high efficiency 8x's have slope efficiencies that directly overlap some 12x's, so it's not that weird if you got the same power.

 

[Slipstream]

Hi igor..

ive ran my 8x and 12x off of flexdrive v4 and v5's ive recently chaged my dead 8x into a 12x and it meausred at 635@12x instead of 620 from an 8X, i have another 12x @ 660 @450mA .i still have another 8x @ 640mw from 460mA. the 12x's are fro plextor drives and the 8x's from LG drives.



in my opinion with 4 8x and 3 12x drives ... the 8x diodes are just as good as 12x diodes at the same current .

 

[IgorT]

The diodes just passed 150 and 290 hours an hour ago.. Next replot at 160h.


For now i'm posting the plots i recorded last night:


The first Murder Candidate:

Diode Stats:
Absolute Efficiency = 17.06%
Slope Efficiency = 1.154mW / mA
Po @ 300mA = 301mW = 84.55% of initial



The second Murder Candidate:

Diode Stats:
Absolute Efficiency = 19.84%
Slope Efficiency = 1.263mW / mA
Po @ 348mA = 397.95mW = 87.75% of initial


As you can see, the drops are becoming quite significant, the first diode is barelly above 300mW, the second dropped to just under 400mW, but they have come a long way before this happened!

If i get a lifetime like that on mine, i will be very happy!


I wonder how much further they can degrade, before popping. I highly doubt it will be to the point where they are usually declared dead based solelly on efficiency. Overdriven as they are, they should poof sometime before they get near to 70% of initial Po.



Degradation comparison in mW:

Degradation comparison in percentage of initial power:

I was kinda hoping to see the second diode cross the curve of the first, but with the bump the first has after 160h, it is becoming quite unlikelly, unless the second diode decides to jump up again.

But it did get very close, still making me think, that the second diode IS actually tougher than the first.



Otherwise, after my personal 8x dropped to almost 425mW after the Medium Custom Lens and had me worried, i was just doing some lens nut measurements and testing in preparation for the CNC lens nut manufacture, and i cleaned the lens after i was done, and my 8x suddenly jumped to 434mW!

I calculated this to be 98.86% of the initial power, so looking at the second diodes degradation plot (in percentage), i take it to mean it hasn't been ON for more than an hour of total time.


And now that i know how much further it will go, i'm not worried anymore, in fact i might even increase the current a little bit if the power drops too low for my taste! :yh:



P.S. I keep updating the Lifetime Guesstimation plot with the latest numbers, and then forcing the curve to fit the little known data, but i don't know if i should post it quite yet. It could be horribly inaccurate.. It seems to indicate too much life for 600mW and more.

Altho if the second diode outlives the first by a lot, the curve could change it's shape entirelly, for now it just keeps climbing up as i add the latest lifetime data up until now.


It's not really possible to make a good lifetime estimation plot with only three known data points, so perhaps it's a futile attempt, but on the other hand, it could provide a rough idea.

I guess i'll post it once i feel satisfied, that it looks right. :angel:

 

[IgorT]

This is unbelievable... We are nearing 180 and 320 hours - only 50 cycles to go!

I don't understand how these diodes can survive being overdriven to three or even four times their rated power for so long!
Out of all 405nm diodes we have known so far, 8x's seem to be the toughest, when it comes to extreeme overdriving.


I thought we would find the ~100 hour point with 450mW, but we didn't. However that's not a bad thing at all in this case.



But this does cause a problem for my Lifetime Guesstimation plot. I'm not sure it has the correct shape anymore, because it indicates too much for 600mW, where we have reports of the 8x diodes dying in a matter of minutes. That's why i'm starting to think it should be bent in the other direction.

The final number of hours of the first diode should answer this (how the curve should be bent - especially if i add a 650mW data point with a very low number of hours close to zero), but the old diode doesn't seem to wanna give up any time soon. Even the second one just keeps on going. :thinking:


I recorded the numbers at 160h two nights ago, but will post a double update at 180h today.



P.S. Another problem these results pose is the question where to test the 12x Murder Candidate.

Obviously we expect more power from it than from 8x's. But the last experiment didn't end too well. At the same time other 12x's are producing 600-700mW and so far working (altho i'm pretty sure most are still under an hour at this point).


I would like to ask ALL 12x laser owners with LPMs to CLOSELLY monitor their laser's powers. It wouldn't be too hard to measure them a couple of times per week to see how much the power is dropping (and how fast)... Additionally it would help, if you would keep an approximate track of time if possible.

It could help a lot with the decision of where to test the 12x Murder Candidate, because after seeing how tough the 8x's are, i have no idea... :undecided:

 

[bryce007]

P.S. Another problem these results pose is the question where to test the 12x Murder Candidate.

I'd say to just take the old 8x off so the 12x can be tested. >300 hours is a ton of hours for a blu-ray pointer.

 

[sportcoupe]

I'd say to just take the old 8x off so the 12x can be tested. >300 hours is a ton of hours for a blu-ray pointer.

The 12x died.

 

[daguin]

The 12x died.

It didn't die, did it? I thought that it just degraded so fast that it scared us into stopping the test. We may find that the "degredation" is really only "burning-in."

There should be another on its way from the 12X GB. We can do a comparison then.

Peace,
dave

 

[bryce007]

The 12x died.

It didn't die, but I wasn't referring to the 12x, I was referring to the old 8x. He could take that off to test the new 12x.

 

[sportcoupe]

It didn't die, did it? I thought that it just degraded so fast that it scared us into stopping the test. We may find that the "degredation" is really only "burning-in."

There should be another on its way from the 12X GB. We can do a comparison then.

Peace,
dave

Dave,
Your statement is more correct then my "it died" statement. I think Igor used the word died due to the extreme degradation that occurred.

 

[daguin]

Dave,
Your statement is more correct then my "it died" statement. I think Igor used the word died due to the extreme degradation that occurred.

Of course mine could just be positive mental imagery as well

I'm hoping when it gets hooked up again, that we will still learn something from it.

Peace,
dave

 

[IgorT]

320 & 180h Update:


First our old murder candidate:

LG 8x #3 320h Stats:
Ith = 39mA
Absolute Efficiency = 16.68%
Slope Efficiency = 1.133mW / mA
300mA Po = 294.5mW = 82.72% of initial Po (356mW)


At 280h the diode was still a fraction above 300mW, but in the last 40 hours it dropped below, but at approximatelly the same rate as during the previous 40 hours.

The diode was a low efficiency one from the start, but at this point, at 300mA it's producing only a few mW more than the best GGW i've ever seen does at 200mA.

It's a huge drop from the starting power of 356mW, however considering the diode is at 320 hours... It's still simply amazing, and means that even the lowest efficiency 8x of all could still be set to 450mW with a reasonably long life expectancy. Perhaps even higher.


Keep in mind, this diode stood far appart from the rest of the group from the start, due to it's extremelly low efficiency. I definitelly didn't expect it to be this tough, but the further it goes, the more i am convinced, that the determining part for a diode's lifetime will be the power setting and not the current required to reach it.

I used to believe the efficiency is directly related to a diode's toughness due to my experiences with PHRs and GGWs, now i believe the relationship is small if it exists at all. At least in healthy diodes from drives, that is (QC reject or prototype sleds could be the exception)....



Another thing i am noticing is, that with this diode Ith is actually climbing up. It started at around 34mA, now it is at 38-39mA, which is a big change. I read about this happening with degradation, but it's something i am not noticing with the other diode.



Also, the "yellow halo" and the other spontaneous emissions (also known as splatter) do seem to be increasing in intensity with this diode. After plotting so many diodes and searching for their Ith, i noticed that the somewhat rectangular projection sometimes called splatter occurs before the diode is even lasing, so it's a part of the diode's spontaneous emissions... I should take some pictures of that.




The second murder candidate:

LG 8x #1 160h Stats:
Ith = 34mA
Absolute Efficiency = 19.77%
Slope Efficiency = 1.256mW / mA
Po @ 348mA = 395.95mW = 87.31% of initial Po (453mW)


LG 8x #1 180h Stats:
Ith = 34mA
Absolute Efficiency = 19.65%
Slope Efficiency = 1.245mW / mA
Po @ 348mA = 393.08mW = 86.68% of initial Po (453mW)


This diode dropped under 400mW after approximatelly 130h, but it's still holding up rather well...


The degradation of both diodes seems much more consistent over the last tests, the speed is not changing too much anymore.



This can best be seen in these two graphs:

The old diode is nearing 80% of it's initial power. If it gets close to 70% it can be officially declared dead.

At the start of this i was convinced they could never degrade that far, considering how overdriven they are, especially since i've never seen more than around 5% degradation before death. Now it actually seems possible the 8x's will live out what is normally their full life, only at an accelerated rate...

 

[IgorT]

I'd say to just take the old 8x off so the 12x can be tested. >300 hours is a ton of hours for a blu-ray pointer.

By "where" i meant the current for the 12x test.

I was gonna buy another counter and a better power supply for the torture chamber, to create a third position...

 

[LarryDFW]

Igor;

This is a graph from Nichia on 320mw 12X BR diodes:

If you want to test at the same power as the 1st 8X diode,
that would be 260ma (from graph) x 150% or 390ma.

For the 1st long 12X test procedure, it probably should not be an extreme overdrive.

LarryDFW

P.S. Nichia did their life test 30 second intervals at 320mw power for 1000 hours.
Almost comparable to your first test procedure of over 320 hours, when you add the 80° C temp factor.

 

[IgorT]

I just looked at the Torture Chamber, and noticed the counters were out of sync. The first murder candidate was showing 20320, the second 11691 cycles. The last two digits were supposed to show the same at all times since they were synchronised.

A closer inspection revealed that the second test diode is producing nothing but spontaneous emissions.


We have our first 8x death...

The second diode (LG 8x #1 @348mA) couldn't take the torture anymore, and gave up at a respectable age of 194 hours and 51 minutes, which is A LOT for an initial power setting of 453mW! During the nearly 195 hours it slowly dropped to just above 86% of it's initial power before commiting COD.


This is probably the first time i'm not sad about an expensive diode dying! I was literally twitching at every click i heard during the first 20 hours, but it went almost ten times as far!

It's dead, but i think it's safe to say it exceeded all our expectations! :yh:
I have definitelly become much more comfortable setting them to around 450mW...

The 8x's are the toughest 405nm diodes i've seen so far! This diode would have survived MANY years of heavy use as a laser pointer.



In the meanwhile, the old diode is at 338h 40m and still going strong. Once that one gives up, i can try to see if it's possible to fit the known values into some sort of a lifetime guesstimation curve....



P.S. The Torture Chamber worked exactly as intended in this case... When the diode gave up, the counter wasn't triggered by the spontaneous emissions alone, and stopped at the final number of cycles the diode survived...

 

[daguin]

Alas, poor Yorrick! I knew him, Horatio - A diode of infinite jest, of most excellent fancy.

Peace,
dave