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FrozenGate by Avery

My 8X at 440mA

climbak said:
Yeah, I have seen a lot of people decanning their diodes so I felt the need to let everyone know the risks to the diode. If you see a continued drop in power from the windowless diode, could you give me a rough estimate of time on and the power drop? I only did a test with a diode in open air with no lens to block it to degrade it purposefully. It'd be interesting to see how well these modules seal the diode from the outside world.
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One problem though, the paper you sent (thank you for sending, BTW) is only talking about UNCOATED facets degrading from oxidation in air. I haven't inspected an 8x or 12x in a microscope, but at least to my eyes under a 'scope, the PHR violet diode looks like it has facet coatings, and I pretty much guarantee the 8x diodes have facet coatings as well. Those facet coatings prevent any oxidation of the facet surface, so I don't think oxidizing atmosphere is going to be degrading the semiconductor surface. Have you looked at the PHR that degraded to see if it has facet coatings? If it does, then facet oxidation is not what degraded it.

Does anyone have a microscope under which they can inspect to see if the other diodes indeed have facet coatings? Especially with the ones at high power, I'd almost guarantee they do, but it's worth looking.

(BTW, for those who might not know such things, how to tell if it has a facet coating: Looking at the facet in a microscope and moving it around, you should see an even color at certain angles of light. If you see a color, there's a coating there. If there's no color, there's no coating.

When I look at the front facet of a PHR diode, I see an even blue color over the whole facet. Blue makes sense, as an HR coating for a violet or blue laser should reflect violet or blue light. Since HR coatings like DBRs have a very wide HR area, it makes sense that a violet HR coating could be a little off-center and look blue, and vice-versa, as coatings on surfaces that small are not trivial to reproduce consistently.)
 





Even with a coating there will still be degredation. I should rephrase a little bit. The actual facet itself is most likely not degrading at all, but the coating will still degrade. The PHRs are coated for sure and I would be really surprised if the other diodes weren't as well. As you saw in the paper it only took a short time before the diode dropped significantly in power. My test showed the same loss in power after several hours and the 30 something percent loss I mentioned earlier after roughly a day of on time. My guess is that the same breakdown of the water vapor is happening and the coating is having the contaminants deposited onto it. This will make to coating lose or gain some reflectivity, depending on the coating, and the laser will no longer be getting the optimum feedback it needed to output the initial power. I will try and pull my test diode out and look at the facet under the microscope and see if there is a noticeable difference to a fresh one.

EDIT: I checked the test diode under the microscope and I did see some structure to the coating. This could have nothing to do with the degredation, but it was different from the normal fairly uniform sky blue color that you normally see.
 
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You can buy mine at 440mA if you want. $300? (no warranty as it is most likely being over-driven but still only has 30 minutes on time so far.)
 
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Uhm, wait ..... uncoated facets ?

As far as i know, any resonant cavity have coated facets ..... how can you create a resonant cavity for light inside a crystal, without coating the facets with a specific wavelenght and reflection/pass coating ?

:thinking: :confused:
 
HIMNL9 said:
Uhm, wait ..... uncoated facets ?

As far as i know, any resonant cavity have coated facets ..... how can you create a resonant cavity for light inside a crystal, without coating the facets with a specific wavelenght and reflection/pass coating ?

:thinking: :confused:
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A semiconductor-air interface is still a mirror. It may not reflect much light, (10-20% or so maybe, I don't remember the numbers for GaN off the top of my head), but it's still a mirror. For many lasers, uncoated facets provide plenty of feedback for lasing.

When we make lasers, we test them all uncoated, and then only facet coat the best ones, because the facet coating isn't worth it if it's already a crappy laser.

Many lasers are even made with an HR coating on one facet, and an AR coating on the other facet, showing further you don't need HR on every facet. You can engineer and design your facet reflectivities to match your lasers and your application. A low power laser will have a very different facet reflectivity than a high power laser on the front facet for this reason.
 
Update on this laser guys. It has been used here and there since it's creation. I thought that the diode was degrading because the power would be lower every time I measured it. Today I measured it and it was at 110mW with the aixiz glass lens (I swapped out the jayrob lens in a better build) I decided that I would attempt to clean the die of the laser diode. To my surprise the laser reacted very well to it's little massage and started to put out 430mW! If you calculate the output with a Jayrob lens this means that the laser is just as powerful as it was the day I built it. I am pretty amazed that I was able to clean the die so easily and effectively. I have ordered some teflon tape to try and seal the diode in the module.
 
jayrob said:
Wow that's nice!

What did you do to clean the diode window?
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It actually was the die inside the can not the window. The window is gone. I used small strands from a microfiber lens cleaning cloth I have and pushed it into the can of the diode. I moved it around in there slowly and repeatedly. When I took it out and turned the laser back on I really had little expectation that it would work again but it did.
 
yobresal said:
It actually was the die inside the can not the window. The window is gone. I used small strands from a microfiber lens cleaning cloth I have and pushed it into the can of the diode. I moved it around in there slowly and repeatedly. When I took it out and turned the laser back on I really had little expectation that it would work again but it did.
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Wow I'm really surprised that bond wires didn't get broken. GJ!
 
cleaning the end of the dye? What did that do? How did that work? What is there to clean? I don't even understand! Nice job though!
 
LarryDFW made a point that at those power levels the laser ion's the air and deposites "gunk" on the die. Thats why we will never see an open can blu-ray like we do with reds.

This also indicates you will continue to have to clean the die, which I'm suprised you were able to do. I can break the laser chips just by looking at them.
 
yobresal;

The output mirror is very delicate.

I would clean the entire chip in an agitated solvent bath.

Acetone works best for diode windows (very flammable).

It has to dry completely before applying power again.

LarryDFW
 
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LarryDFW said:
yobresal;

The output mirror is very delicate.

I would clean the entire chip in an agitated solvent bath.

Acetone works best for diode windows (very flammable).

It has to dry completely before applying power again.

LarryDFW
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I found using Acetone leaves a white residue on a black surface, and I did a lot of research and spoke to a few guys over at PL... This was mainly for lens cleaning so I'm not sure if it applies here.

But basically I got told to use acetone, and from there use a pure isopropanol after to remove the acetone residue and if cleaning a lens, use a wooden sticked q tip, since the plastic ones can melt and dissolve in the acetone along with the glue sometimes used.

I personally got hold of some acetone at the Chemists, but isopropanol I was refused, which was frustrating and was told they can't sell it.
 
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