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I assumed they are binning info.
dont think it matters much...might as well have been stamped "this garment approved by B6"Quote:
Originally Posted by mpoulton
EDIT-----interesting......................................
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"I also want to know: How the hell do you sleep at night knowing that you are supplying WickedLasers?"
hate to sound like a rep , cos i aint , but i appreciate their innovations for the future ..... with the smartswitch and low power lens and safety glasses the WL product is going to be the safest out there ! The loads of hobbyist and builders selling hand held 445nm with no safety features ...yes its maybe just horrible that they are out there in the first place but so are guns and landmines ..it was gonna happen someday ...and at least WL have made an attempt at safety
As regards array marking ..really aint got a clue
paul
@"Smart switch" - Load of cobblers...
@Diodes - check the part no...
From what I understand about these markings: the arrays are tested and graded according to output, I assume this is done by the diode array supplier so the projector batches have some consistency, could also be related to a production line reference. Apparently the 140s have far better diodes than 130s.Quote:
Originally Posted by mpoulton
Slope efficiencies...
I will add that most of my XJ-A140's have had a B code on them, precisely one of them had an A code. They also have a number written in sharpie elsewhere on the array, usually 17
Has anyone else noticed significant variation in the output power for diodes across an array? I thought some of them looked a little dim, so I took IU curves for an array and was amazed at the spread
Attachment 19045
There is some slight variation due to the test, but after spot checking a few diodes I would say its within ~+/-25%, so the factor of 2 difference is disturbing
There is some slight variation due to the test, but after spot checking a few diodes I would say its within ~+/-25%, so the factor of 2 difference is disturbing[/QUOTE]
Is this really +/- 25% or do you mean +/- 2.5% cos if not a factor of 2 would be kind of statistically fairly reasonable.
For same diode at -25% say 750mw and different test +25% = 1250mw.
So a <20% real variation between diodes could give this result.
Unless I am missing something here!
What are the units of the Y axis labeled x.00E.400 ? :confused:
In fact there is much more reported variation posted all over the place though most will be due to other factors ie. driver current and optics setups.
Probably the unkoolled "pointers" with extra high power >:) will be used a lot to pop thousands of balloons and acquire somewhat less power as a result.*vigil
Anyone interested in starting a black balloon GB just to make sure ? :D
Anyone got any max TEC hysteresis recommendations for collimator blocks. I have to decide whether to use indium solder paste in loose mounts or whether this is total "overkill" . :cool:
Cheers! :)
The A140 I bought has an A written on it, along with a 7. I have yet to remove the diode and test them though. Is there really a difference between any of these arrays?Attachment 19071
There is only one way to find out...
I am hoping to get something other than a B grade in my next shipment, but if not would you be willing to sell the A graded one to me for testing?
Per my graph, the values are currently +/-50%, typically I was seeing about 5-10% variations comparing a diode to itself, so the spread is significant.
edit for catalanjo's edit
the Y axis is not in mw because I have not decided how I want to rate the output power, coming from the raw diode, after a lens lens, etc. It is currently the raw reading from my meter.
You're getting some pretty major heating on those diodes for them to be rolling over that much. Try doing it without the heating, meaning either 1) pulsed measurements, which you may very well not be set up for, or 2) more heatsinking or temperature control, longer cool-downs, etc.Quote:
Originally Posted by krazer
You just seem to be getting a lot of roll-over, that I haven't seen as much elsewhere, in addition to that huge variation, which I also haven't seen as much elsewhere.
The diode was clamped in a thorlab diode mount (LM9F) on a coldplate at 25.0C. The duration of the sweep is ~50ms, I tried taking sweeps with more points, but started to notice significant heating effects, the 15 point sweep didn't show significantly less power than a 3 point sweep. I did observe significant power loss when running CW, but when running the sweeps I graphed I do not believe heating to be a significant source of the variation.
I am currently working on finding the sources of error, the thorlabs diode mount really just doesn't seem to cut it for a diode of this power. I was suspicious of my photo diode for a little while, but I added a od2 filter and the shape remained unaffected so I do not think it is due to issues with the detector
Does anyone know of a good quick diode mount which has good thermal properties? I was hoping the LM9F would work well since it clamps on the whole outside perimeter of the diode quite securely, but the CW measurements don't lie. I have a big fat aluminum block style mount (nearly identical to that used on the projector) which I hope to compare to when I get my next lot of diodes in, but swapping diodes into it takes 4 screws and is quite tedious when testing whole arrays. I am seriously considering getting set up to test the diodes before they have been removed from the array; I have a few ideas to make that work but I am not sure I will have the time to get that set up in the upcoming weeks.
I am also getting a grating based spectrometer in the next few weeks which will allow me to monitor the wavelength and calculate how much the die itself is heating, I was hoping to use my wavemeter but these diodes have such a wide spectral width (over a nm!) at high powers it doesn't have a chance of getting a reading.
I was also considering looking at the voltage drop, the temperature of a diode does have a measurable effect on the voltage drop, but I am not sure how close to an ideal diode these diode are. It is a kind of chicken/egg problem, if you assume the diode is ideal you can easily calculate the die temperature, or if you assume the die is at a constant temperature you can easily measure n, but you can't do both at the same time :rolleyes:
One final observation, only the lower power diodes show significant amount of rolloff, the high performers just keep on rising.
Semi-related question, since you appear to be online right now...are you doing all this with home equipment, or in a lab at UCSB?
And heating may not be the cause of the diode-to-diode variation, I don't understand what the difference could be there, but it is still the cause of the rollover. Test pulsed, and the rollover won't be there. It could be that some diodes are more sensitive to the heat than others in your tests? Curious results, none-the-less.
Very nice that you do have some active cooling and other nice equipment, it seems.
I am doing this at home, I am a big fan of quality (used) test equipment. I have however been known to take diodes into the lab to use the OSA or take a nist traceable power reading...
In any case, your comments inspired me to pull a diode out of my 'for projecting images use only' projector, and comparing a single pulse measurement to the 15 point sweep measurement there was a ~10% droop at 1.5A. I am not sure how I didn't notice it earlier, perhaps my test diode showed less of a variation with respect to temperature. Hopefully that will explain the rolloff, if not the variations in power.
Time to go back to designing a better test setup...
Hey Krazer,
I want to keep the 'A' array, but would sell you some diode's if that would help in any way.
-g