LPC 826 658nm diode tests/infos

[Solarfire]

Hi all,
I was just silly dickin around a bit today while I was harvesting diodes out of some 815 sleds + I got a dozen of the 826 diodes in, so I did a little bit of testing (quick tests) and thought I’d share my findings.


My main Interest was the issue power loss after collimation. The graphs were all done with the same diode starting with 100mA in 100mA steps up to 600mA. One graph of raw power (no optics) was done for reference. I forgot to change the legend in the graphs; the Y axis is power in mW.


The 815 and 826 are not the same diode. Raw power measurements of the 2 gave on average max. 250-270mW @ 400mA for the 815 and 390-400mW @ 600mA for the 826. During testing the 815er bit the dust while adjusting up to 400mA. After having read that others have popped the 826 @ 650mA I decided to limit @ 600mA.


I did some measurements with different collis with some amazing results with blue AR coated lenses giving better results than some red AR coated. I got best results with the 405-G-2 with less than 5% loss and with the mccarrot blue with <1% loss? Yeah… I’m still scratching my head on that one, but I double checked it and it’s so. I didn’t do a graph for the Axis red since these showed losses of > 20%.

Taking into account price, beam size/profile (<2mm @ aperture) and power loss I may end up using the 405-G-2 lens in some red setups.

[LaNeK779]

thanks for doing this mate, it was really enlightening!

i have also thought about using a "blue" lens for red but i gad no way to test it

[laserwinkel]

great graphs
any idea on the temperature at 400mW ?
and what heatsink are you using?
mine probally popped at 650mA because of the heat

[Solarfire]

great graphs
any idea on the temperature at 400mW ?
and what heatsink are you using?
mine probally popped at 650mA because of the heat

Like I said, this was just a quick run thru. No temp regulation (ambient 22.7°), short (<5min. total on time) test. Aluminum diode mount 15mm x 15mm x 22mm
Mount temperature change insignificant during test period and current range of min 100mA to max 600mA

Stress test pending. If it dose 400mW CW, TEC'd with the right lens then I'm happy

[planters]

A couple of months ago I did some torture tests of the LPC-815 diodes harvested from 20x sleds. I was not aware of the 826 diodes. Could you go into their source,the way to identify and other differences with the 815s. I ran the diodes raw and through an Aixiz red lens I also recently looked at the 4mm fl. aspheric from Optima. The heat sink was TEC cooled backed up by a lab chiller, but not regulated and temperatures down to -50C were looked at. One diode survived for 36 hours at 420ma at -30C. Another survived for almost exactly the same 36 hours at 390ma. A third diode survived for 12 hr at 550 ma. at the same temperature. Over the full tempreture range the wavelength shift was 0.2 nm/C. The Optima lens is impressive. Near-field 2x3mm with a 0.5 milliradian divergence and output was 30% greater than the Aixiz lens. The output through the lens was within the measurement error from the raw output! In all cases the output improved slightly, but steadily ( max. aprox. 5%) at the lowest temperatures. And except for the temperature effect the output was linear at 0.7mw/ma over the entire range above threshold. At -50C the output is significantly brighter and more orange.

[Stoney3K]

At -50C the output is significantly brighter and more orange.

So the wavelength will shift towards the 650-640 end when you chill the thing down enough?

I guess it's time to start thinking up some design with a beefy TEC, sealed optics and a custom water jacket. 500mW of 650nm from a single 10-buck LPC826, now THAT sounds like an interesting experiment.

[LaNeK779]

and another conclusion is that if you run an 815 and an 826 both at 400ma, the first will die and the second will have much more headroom, so increased life-span

i think that is a major benefit...

[Stoney3K]

and another conclusion is that if you run an 815 and an 826 both at 400ma, the first will die and the second will have much more headroom, so increased life-span

i think that is a major benefit...

I think the wavelength shift is something very interesting to look into. TECs can cool these things down to some insane temperatures, and direct diodes run BETTER when cold.

DPSS needs very stable temperature regulation to keep the crystals in their operating parameters, that's where the home-built TEC drivers have been designed for.

For diode lasers, it may be better to slam the TEC open to the max and chill it down as much as possible. Sinking the excess heat into something else won't be much of a problem, we've pulled the same trick on PC water cooling systems for 2 decades.

Chill a 650nm LOC down to -30, and it becomes a 640nm diode for next to nothing, with more potential to run longer at high currents. Win-win situation if you ask me.

The only thing you might need to watch out for is condensation. That's easy to combat by sealing your entire optics cavity (and, if you want, replace the air with a dry gas like nitrogen).

[LaNeK779]

Chill a 650nm LOC down to -30, and it becomes a 640nm diode for next to nothing

i'm with you for the majority of what you say, and i am no stranger to pc tec-ing and watercooling myself. i even have a couple of amd athlon xp cpu waterblocks around from the old days

my only objection is the absence of hard data (measurements) of how much the wavelength shifts with temperature. at the moment, all we know is that it turns a bit to orange, not that it approaches 640 wavelengths.

i can only wish that someone with a "wavelength meter" gets to it and can provide even a slight hint that we approach sub 650 area. then i'm off to the shed, with tecs and blocks in hand

[p1t8ull]

my only objection is the absence of hard data (measurements) of how much the wavelength shifts with temperature. at the moment, all we know is that it turns a bit to orange, not that it approaches 640 wavelengths.

I have no hard data on these but the DVD diodes I have looked at tended to hover round about .3nm per deg/C shift.

Norrra lot!