Kaidomain 50mW CR2 - inital review

[bob12345]

Don't worry if you lost the output, the laser can be very erratic when messing with the crystals. Just take it apart and put it back together, I had nothing but IR coming once but this was fixed exactly so.

How bad would a reflection be? I turned it in 30* increments and it seemed to do nothing major.

 

[Benm]

I just hope i can revive one from the parts of two. How the hell did you guys manage to turn the diode without losing green? The DX200 was actualy easier than this.

Turning the diode could result in a fatal reflection from the brass. Damn. Trial and error is pretty much out of the question.

I found it surprisingly easy to get the green back from the one where the MCA came loose. Just holding it down in front of the pump diode resulted in some green, even when rotated to its original position quite a bit. I superglued it back into place (as well as i could, which isnt exact) and then rotated the diode for optimum green. Fixed the locking ring and it's been working ever since.

I expected it to be much harder than it was really - something like aligning the mirrors on a gas laser - but i proved to be dead simple with decent results as well.

 

[IgorT]

I really don't know what happened. I'll try to fix them later today. But i went for the entire circle and got no green.
First i need to check the diodes through a magnifying glass, to see if i damaged something, even tho i can see some IR glow.

So you had the diode loosened and powered on? Or even outside of the module and powered on? I'm afraid it would burn up if i did this.

 

[IgorT]

So i now have two dead KD50s. One died from the current being too high (good one), and the other just from being taken appart (used one).

I did manage to find an alignment in the good one, where it produces 10-15mW of green again. But due to the off center position of the crystals turning the diode doesn't really help. I thought it was the diode, but the other one is behaving the same way, except, that i can not find the original alignment anymore. I think there is a reason for the crystals being off center. Maybe the fast axis spreads more in that direction as well.

If i put the diode from the good one into the used one, i can bring those crystals to glow, but not the other way around. I also noticed, the used one has different crystals, which are in one single piece, and are square, while the others are wider in one direction..


It doesn't seem like there's much, that i can do this way. Maybe if i took the crystals off and really reposition them and glue them back in place. At the moment, i don't have much to loose, but this could be very hard to do without special purpose tools.


Ben: How did you manage to keep the crystals in the perfect spot for glueing? Or did you just do it, and it worked? I think i'll need to do the same, if i want them to live again.
I was thinking of using superglue in the DX200, but i was afraid of what those nasty vapours could do to the optics and the crystals. Epoxy doesn't have such corrosive vapours, but is too messy.



BTW: The only remaining KD50 just peaked at 80mW for the second time and then at 82mW after that. And for some strange reason it doesn't happen with a full battery. Putting it into a cooler helps, but is not necessary.. If only it would remain above 50 a bit longer...
EDIT: My only remaining KD50 just peaked at 105mW on a full battery, after being taken from the cooler! WTF?!? This one would be amazing with a peltier! I also figured out, that one of my 1AA flashlights could actually fit my tiny 15mm peltier! This could get interesting. But i would have to design a very weird shaped heatsink. I think this one absorbed the life force from the other two..
EDIT EDIT: 125mW on the bad battery! This one really loves being cold, and would definatelly be worth putting into a different host with a peltier, even if it is a lot of work.

 

[Benm]

Ben: How did you manage to keep the crystals in the perfect spot for glueing? Or did you just do it, and it worked? I think i'll need to do the same, if i want them to live again.
I was thinking of using superglue in the DX200, but i was afraid of what those nasty vapours could do to the optics and the crystals. Epoxy doesn't have such corrosive vapours, but is too messy.

When the crystal set came off, i just turned on the laser and held it in front of the diode by hand - some green came out at a random position. Then i just glued it in place with epoxy on the position where it looked like it was orginially (i could tell roughly from the glue remains).

As for the vapours, you're right, those could easily stain lenses, coatings and what not... must have been lucky.

And for the 125 mW producing unit: That's pretty amazing. Perhaps you could just make a tabletop module out of it with TEC keeping it at the optimum point.

 

[bob12345]

120mW, that is obscene! Nice work but are you overpumping the crystal to get that?

 

[IgorT]

No, i didn't do anything. I just put it in a small peltier powered cooler for drinks. It doesn't really cool that far down.

And yet i got even more than that! I think it was 134mW or so, but i'm not sure cos i was taking pictures and looking through the camera. Unless my meter got unbalanced, it is real.

I'm recharging the meters batteries at the moment, to check again.


EDIT: Ok, i feel stupid now. I actually took pictures of my meter showing 135mW with the KD50 and at that moment it actually stung my skin a lot, so i believed it... But after i recharged the batteries, it again doesn't show more than 76mW peak at best. One of the two batteries in the meter got empty, and the meter started acting up. I should add some Low-Battery warning LEDs.

Still, 76mW isn't bad, but it's not worth building that peltier monster. Instead, i'll use that for an open can.

 

[Benm]

Too bad about the meter over-estimate, but 76 mW is still a very good result!

I took a closer look at the dead new KD50. It seems that the photodiode pin is connected to the board in this one (in the old version its not soldered at all), but i'm not sure it actually does anything.

Also, here is a picture of the guts showing a working pump diode but no green at all. I'm sorry about the bad quality, my camera doesnt pick up the IR much, in reality is deep red but well visible to the eye, the cam makes it blue-purple.

These shots had to be taking with short exposure times since i was holding things by hand, and the diode has no proper heatsinking in this setup. Rotating the diode with its ring unlocked didnt do anything either - and KD seems not to be responding to support mail.

Knimrod offered me to send the MCA from his dead KD50, i'll try mounting that in this laser to see if it has any result.

 

[IgorT]

Well, at least you have a good pump.

I just broke the crystals off on one of the lasers, so i could measure both diodes.
The one i overpowered measures 125mW, and the one i just misaligned measures 1mW and only takes 60mA for some reason i don't understand. Might have broken it while tightening it or something. The ideal reason would be a bad solder joint or something else on the circuit, but i doubt it. And i don't think 125mW of IR is enough for 50mW of green.

Neither of these two measurements make much sense to me. Usually, when i kill diodes, they lose all power, and not just a part, but the current doesn't change even without current regulation.


It would seem i need new diodes, if i ever want to fix the lasers. Unfortunatelly, i'm afraid they would cost more than a KD50. And a can wouldn't fit in there... Damn. Looks like the crystals are good tho.

I doubt, that the diode in this type of lasers is bad somehow, so current regulation could actually prevent them from dying, by maintaining a reasonable power, but preventing current spikes with full batteries. Need to draw some boards.



EDIT: I just found some 200mW 808nm diodes on e-bay, and the spec sheet says operating current is </=290mA. Could be the diodes in the KD50 are 200mW units, being slightly overdriven, depending on the batteries. But how can a diode lose just one third of it's power?!?
Treshold current is listed as 60mA, which is what i measured on the other one, that only puts out a mW or two. Gives me hope it could be something else.

 

[laserfunny]

Is the KD50 adjustable?

 

[Benm]

But how can a diode lose just one third of it's power?!?
Treshold current is listed as 60mA, which is what i measured on the other one, that only puts out a mW or two. Gives me hope it could be something else.

A diode could use part of its power by (thermal) degradation, similar to what happens to (high power) LED's after many operating hours at elevated temperature. But it should still draw the same amount of current, just produce less light for it.

If it draws only 60 mA, there is a problem with its power supply, or its totally shot - not died of COD, but the actual lasing medium burned out.

If you want to replace the pump, i'd make very sure you get something that actually fits. The diode in de KD50 seems somewhat odd - it has a 5.6mm base but looks a bit 'shorter' than most others (?).

 

[IgorT]

If you want to replace the pump, i'd make very sure you get something that actually fits. The diode in de KD50 seems somewhat odd - it has a 5.6mm base but looks a bit 'shorter' than most others (?).

Cans don't fit in there, which is a shame, on the other hand a 200mW "canned" diode costs $12 + shipping, which would end up costing as much as a new laser, so it's not really worth it.
My only hope at the moment is, that the other one is alive.

Otherwise i've heard, that the typical conversion efficiency for the crystals is only 10%. More efficient crystals should be very expensive, so i really don't understand, how these NewWish lasers can produce 50mW from 200 or ~200mW from 0.5W.

I'm gonna do a test with an IR filter, to see how much of the power comes from that. Unlike the DX200, there is no spreading IR noticable on the camera with the KD50. And the distance of the laser does not affect the power reading. I don't think, that there would be a lot of IR in the same narrow beam, but i guess i'll see. On the other hand i just remembered, that LEDMuseum said on CPF, there was hardly and IR measurable on the spectrometer.

 

[Benm]

There isn't much IR when operating normally i think, but when the crystals fail and no green comes out any more, it is visible. It's not very focussed however (comes out in a several degree wide pattern), so if you take the measurement pointing at the sensor from a foot away, the IR contribution to power should be negible.

As for conversion efficiency, i guess it can be rather good at the correct temperature - one of the things that give all these lasers big output variations with a bit of warming or cooling.

 

[IgorT]

Yep, i'm just surprised how this temperature varies from one to another.

Yesterday i managed to mount the remaining KD50 into the head in a way, that provides just a bit more heatsinking, and now it is capable of remaining above 50mW for much longer. Before it would drop to 35 within a minute. Now it stays above 65mW for almost two minutes, and it takes another two to drop to 60. After that it takes another minute to drop to 50, but once there, it starts dropping fast.

I left it on for 10 minutes and it dropped to 38, but as soon as i put in a fresh battery, it would jump right back to above 50 so it'll even get a little better with a driver.. But it's surprisingly stable as it is already.

I was worried, because i killed the one that was climbing with heat, but this one looks like it can do even better.
I rarely leave a laser on for more than a minute, so as long as it remains at optimum power during this time, i'm happy with it, which means, that i'm more than happy with this one now..

 

[freshert]

i think i bought one of these lasers off of ebay (hasnt arrived yet)... looks exactly the same and same box... do u guys think it will be okay or do u think it will be a piece of rubbish? i bought it before i knew about this forum. :'(

 

[IgorT]

Was it a french seller? If it's the same laser, it should be ok. How much did you pay?

It's possible it is a drop shipment and will come directly from KaiDomain or DealExtreme, if it's the DX laser that looks the same from, but is listed as 30mW. What did the description say? Post the link.


I also noticed another laser on e-bay, that looks identical, but is being sold as 80mW, together with a weird "Laser Power Meter" of sorts, for almost $300. I wonder what that's about.