NEW LOC Laser diode review.

qumefox · Jul 12, 2010

FYI, the 445 casio diodes appear to exhibit the same fallback that is being discussed here. I'll have to hunt again, but i've seen video of one being pushed past 2.3A and the output falling off more and more with higher current, then returning again when the current was lowered. With those though, i'm not certain it's a protection method, as noticeable facet degradation begins well below that current. However it's still apparently hard to instantly LED them, similar to the diodes your discussing.

When I first saw it I thought facet power handling had just finally exceed what the diode material itself was capable of, either thermally or due to frequency shifting due to lack of stability at high currents.. but I guess that's not the case.

Hemlock_Mike · Jul 12, 2010

Qum-- -

Wavelength shift has not been addressed because very few of us here have equipment sensative enough to read nM vs temp, power, time etc.
HMike

Benm · Jul 12, 2010

Well... there is a way to indirectly measure the temperature of the die: by its forward voltage at a specific current. I could do some tests on this: run it at 700 mA or so for, say, 30 seconds, and then back to 200 mA for another 30 seconds. Any thermal effect shoud be visible by the forward voltage just before going to 700 and just after dropping back to 200.

The drop in visible output is not explained by thermal shifting though - i'm looking at power using a thermal sensor that really doesnt care if the light is 700 or 650 nm. Perhaps it does shift up a little at high current due to the heat, but that is perfectly normal. I doubt its enough to see on a simple grating test.

Hemlock_Mike · Jul 14, 2010

Benm ---
I stuffed the third and last diode into the housing tonight and it is a rubber stamp of the previous two diodes. Foldback starts at about 400 mA and PO is almost the same.

HMike

Benm · Jul 14, 2010

At least they are very consistent then. I've done some tests on voltage drop vs temperature and current, but those didn't reveal much extra information,

After running all of these tests, i can recommend these diodes for anyone that wishes to build a 200 mW+ laser pointer without risk of driver mis-adjustment. These are by no means LOC killers in terms of performance, but they do seem exceptionnally sturdy, allowing virtually foolproof design when aiming at 400 mA or so.

In that sense these diodes are special - virtually immortal unless you push them so far you melt the bond wires. Also, these can be good for projectors - despite all the abuse i've given it, the diode performs as well as it did when i got in in the mail from you... remarkable considering what i did to it

Hemlock_Mike · Jul 14, 2010

Benm -- Remarkable too, considering what I did to it before I sent it

...
Greg says the distributor is pissed at my findings :scowl: GOOD. I told Greg to have him call me.

HMike

qumefox · Jul 14, 2010

Hemlock_Mike said:
Benm -- Remarkable too, considering what I did to it before I sent it ...
Greg says the distributor is pissed at my findings :scowl: GOOD. I told Greg to have him call me.

HMike

Why would the distributor be pissed that they have almost unkillable diodes? Seems like that would be a selling point.

Pontiacg5 · Jul 14, 2010

I think they were supposed to be stronger

Benm · Jul 14, 2010

I suppose so - there was talk of '50% more than LOC' or something similar, which they clearly don't live up to. At least not for peak performance - perhaps if you look at a 10.000 hour survival times, these could be run 50% higher than an LOC and make it to the end safely, altough we only have a few days worth of test fires so far.

As far as i'm concerned these diodes are a good product and should hit the market. I'm sure kipkay will love them too as these are more likely than not to survive the mini-maglite abuse, albeit at limited power

SenKat_Stonetek · Jul 17, 2010

Benm said:
I suppose so - there was talk of '50% more than LOC' or something similar, which they clearly don't live up to. At least not for peak performance - perhaps if you look at a 10.000 hour survival times, these could be run 50% higher than an LOC and make it to the end safely, altough we only have a few days worth of test fires so far.

As far as i'm concerned these diodes are a good product and should hit the market. I'm sure kipkay will love them too as these are more likely than not to survive the mini-maglite abuse, albeit at limited power

Thanks, Benm and Mike for your hard work in testing these diodes ! The MAIN problem I have with them, is the distributor

They want TWICE as much for these than they do for the LPC-815's ! NUTS ! They were also advertised as capable of 500mw + Well..... That is two for two against these diodes. If folks are interested in purchasing these diodes, email me and I will get some sent out, but unless the distributor lowers the price on them, I will not offer them as a standard item in my shop.

///Greg

Benm · Jul 17, 2010

Twice the price wouldn't be justified indeed! Practially speaking you could then just get 2 LPC815 diodes, potentially blow one up and adjust your driver back down for the same money.

If they would be about the same price as the 815 diodes they'd make a fine addition to your store though - a very reliable 200 mW+ diode for applications where low failure rates are more important than raw power.

Honestly i think we will not see much more powerful diodes from/for dvd burners at all. Dvd is being replaced by bluray, and faster dvd writers are probably not worth the development and research costs involved. Also, at some point you just can't spin a disc any faster reliably - in fact, i think laser power isn't the limiting factor anymore.

SenKat_Stonetek · Jul 17, 2010

I'm pretty sure you have a valid point about the lasers not being the limiting factor any longer....perhaps we would suffer bit and byte impalement if they spun too much faster !

Benm · Jul 18, 2010

Well, the thing is that they make the rated max speed only on the outer tracks for the disc, since linear speed is greater there for a given rpm. CD drives used to have the same problem.

The next more powerful red diodes will probably come from projectors, just like the crazy powerful 445 nm ones do. The roadmap to better red diodes will be shorter wavelenghts and increased power, but very possible at the expense of going towards multimode units.

Surely th beamspecs of these new diodes you acquired are good - comparable to what we are used to from 815 diodes. Its just too bad that there is some power limiting system incorporated that limits exploring full potential. It also eats away at effiency - at 400 mA you get way more poewr from an LOC than from these ones, although the LOC will not survive that for very long.

SenKat_Stonetek · Jul 18, 2010

Well, as stated before, the quest shall continue

I WILL get some inexpensive 500mw+ diodes in - and I'll send them out for testing to as many folks as possible so we get a great cross section of data - you and Mike did a most thorough job testing these, and again - many thanks to both of you !///Greg

LASER66 · Jul 22, 2010

what is the price on these new 822's? Did not see it on stonetec.
Will

SenKat_Stonetek · Jul 23, 2010

LASER66 said:
what is the price on these new 822's? Did not see it on stonetec.
Will

You didn't see it, because I decided against carrying them - their cost price is twice as much as the LPC-815's are, and that decided me.///Greg

NEW LOC Laser diode review.

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