great job, thank you!
..so you were right, they all are perfectly linear, no kinks, no knees or similar! yay!
manuel
Yes, starting from 100mW CW / 200mW Pulsed, kinks seem to be gone with 405nm's for good!
BUT... As mentioned before, there is at least one case where a kink
developed later through degradation with an 8x - Hemlock Mike reported it on a diode that used to do 400mW+, still starts there but drops rapidly with it's beam splitting into two...
The good news is, he says he was among the first to make a 400mW+ 8x laser, meaning it lasted quite a while before this happened only question is how much it was used in that time... I also don't know what the efficiency of his diode was (is his diode among the plots Franco collected?)..
In any case, this means i need to be careful when testing these 8x's, make sure i replot the diode DURING the test several times, perhaps every four hours (4h of run-time = 8h cycling time), so as not to miss this if it happens, and of course to record degradation....
Now that the diodes are already plotted, testing for degradation will be quick and easy. I just need to measure Ith, 40mA and 280mA, after letting the diode cool down for a bit....
- Degradation would show in an increase in Ith and lower powers at previously tested steps - 405nm's supposedly degrade by Ith climbing, while the slope efficiency remains the same - the plot just shifts to the right.
- A kink would show in powers up to a certain step being the same, but at the higher steps they would drop drastically.
Otherwise, while testing i decided to go to 280mA with all diodes, so as not to have to extrapolate four steps for every diode.. The accuracy would be reduced - especially in the Po/Pe plots....
I kinda doubt anyone is interested in much less than 280mA with 8x's, so i thought it wouldn't hurt to go that far for a quick plot (only takes seconds to check the numbers and quickly turn the current back down). Going to 360mA really would be too much, before we even know how long they last.. The last two steps (320 & 360mA) are what i'm extrapolating...
Power vs. current is easy to extrapolate, since it behaves pretty much linearly (well, it does drop a little with every next step, but it's easy to predict). But i wanted to compare diodes according to their actual efficiency. And for that i need their Vf.
Extrapolating the Vf is the hard part.. Basically i would have to find a pattern of how it behaves, and then continue it... But since with two diodes i actually went to 360mA, i have their Vf plots, and could adjust the others so they have the same curvature.
But even better than that is using the Efficiency Plot (% of Pe), because it drops somewhat linearly after the peak, and if i have Po's (which are easy to extrapolate) it only depends on Vf... That way i can adjust the Vf until the efficiency drop matches that of other diodes, and make approximate but pretty accurate Po/Pe plots up to 360mA without having to push the diodes there...
Only question left is, when i hook it all up to the cycler, what current do i set the first diode to? The lowest efficiency diode only produces 336mW at 280mA.
At 300mA it would do just over 360mW.... We said current specific testing and 300mA for the first one.
But since it stands quite far appart from the group, i was wondering if 280mA might give better results, closer to those of an average diode at 300-320mA perhaps....
This is of course a guess based on the assumption, that efficiency equals, or rather is closly related to diode "health"..
I don't have a lot of evidence for this, i have not killed enough GGWs to proove it, while PHRs were not consistent enough.. In one experiment a low efficiency GGW was the first to die at 200mA (only a few hours), while the normal or high efficiency ones "out in the wild" all still live...
For now it's just a feeling... But it would make sense...
Otherwise, here is a photo of the testing setup i use for plotting..
The big heatsink was a present from Tallaxo, attached to it is the head piece of a v3 Heatsink/Module.
This particular module is slightly different, in that it allows me to press a diode in, where it is grabbed firmly, for good thermal contact, but also allows me to safelly remove it afterwards.
The heatsink is big enough, that i can make a full plot, and when i go back to check the previous steps, they still show the same power - no drop from heat.. During plotting the heatsink is on a plastic stand i made to hold it at the height of my LPM's thermopile opening.
I wanted to add a third display to the Diode Analyzer for temperature, already put the module in the enclosure, but it's getting tight on the panels (i'd have to move the switches to mount a third display). Besides, while it would tell me the temperature, it would not respond nearly as fast as the Vf does.
Basically, when i'm plotting a diode, i use the Vf display not only to write down the voltage data, but also to watch for any temperature drift... If the Vf would start dropping, i would know the diode is warming up and the plot might be affected....
The Vf changes MUCH faster, than the temperature would, besides, the temperature probe would measure the heatsink, not the diode, which means there would be a considerable lag.... The Vf directly corresponds to the die temperature on the other hand.
Because of the size of the heatsink, the Vf stays put during plotting, but if something was wrong (if the thermal transfer was imperfect at some point) it would immediatelly become apparent in Vf.
Anyway, this is the heatsink i am going to use for the Cycler test, except with another module head, which is meant for permanent installation...
Otherwise, i have to "calibrate" the sensor now. It has to register powers over a wide range, but at the same time not respond if the diode goes LED (or 5~mW like the F03's - just in case), so it needs a "callibrated diffuser", partially so as not to fry the photo transistor (already killed one with my 6x :yabbem
, and to stop it from registering below certain powers...
