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Strange behavior of the red laser

Petersoft

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Hi. I have a question. I recently built a laser from a DVD burner. During the experiments I decided to light this laser in the mirror so that the laser beam reflected back to the laser and at that moment the laser diode got damaged (typical damage of this type of diodes consisting in that they begin to glow very weakly and warm up much more). Do any of you know why this happened? if so, I would be grateful for your answer. greetings
 



gazer101

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The laser light likely caused the die to heat up and stop working (possibly due to heat-induced oxidation?)
 

Ramsey_innovations

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Yep, sounds like COD (catastrophic optical damage). I bet if you look at the tiny facet on the front of the semiconductor you'll see that it's burnt. Of course disconnect the power/batteries before you look at it just to be safe.
 

gazer101

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Doubtful, considering the active emitter area is about 1x2 micron, which is ~20 times smaller than a human hair.
Maybe the laser light blackened the window somehow then? Why else would the laser become so dim after getting lasered?
 

Ramsey_innovations

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Doubtful, considering the active emitter area is about 1x2 micron, which is ~20 times smaller than a human hair.
Yes it's very small, you'll need to use an eye loop or microscope to see it well but it's bet it's there. I've seen it before....i learned about back reflections the hard way about 12yrs ago. My very first diode build actually. I picked up several 9mm 660nm ~100mw diodes from a NASA contractor surplus store. From what i remember i think i was messing with a first surface mirror and passed the beam reflection back across the diode...instant death. I clearly remember inspecting it under magnification and seeing a burnt facet. You know, you CAN see damage on a facet that small with just a moderate power magnifying glass too, just look for the reflection of your rooms light across the surface, anything substantial will be noticeable.
 

Cyparagon

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Why else would the laser become so dim after getting lasered?
To be clear, I DO agree this is COD. I do NOT agree that it is an easily visible fault.

Yes, technically, all electrical faults are just mechanical faults. Yes, ESD damage is visible with an electron microscope following a week bath in an epoxy solvent. However, It doesn't mean you can "see that it's burnt" when you zap a chip though. That's misleading.
 

Ramsey_innovations

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To be clear, I DO agree this is COD. I do NOT agree that it is an easily visible fault.

Yes, technically, all electrical faults are just mechanical faults. Yes, ESD damage is visible with an electron microscope following a week bath in an epoxy solvent. However, It doesn't mean you can "see that it's burnt" when you zap a chip though. That's misleading.
An electron microscope is not necessary...unless you have boomer vision or something... Yeah I'm calling bs... This morning i was able to replicate exactly what i was talking about using a magnifying glass and a collimating lens. No editing or cropping on the photos....My phone camera makes it look smaller, it's quite easy to see it in person.

This is the setup...


This is what a good facet looks like...notice the clean reflection of light across the facet.


This facet has a chipped corner in the upper right portion.


This facet has a burnt spot in the center...
 
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Ramsey_innovations

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Cyparagon....where did you go? So quick to doubt and post a rude comment & gif....anything else to say now?
 

Cyparagon

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HA, your skin is thin enough to consider "doubtful" to be rude? Fucking welcome to the internet, buddy. You'll do very poorly here.

Was your diode damaged by COD - specifically back-reflection type? If so, I may stand corrected, although this isn't a very impressive sample size.
 

Ramsey_innovations

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HA, your skin is thin enough to consider "doubtful" to be rude? Fucking welcome to the internet, buddy. You'll do very poorly here.

Was your diode damaged by COD - specifically back-reflection type? If so, I may stand corrected, although this isn't a very impressive sample size.
Oh man i feel bad for you....honestly. You think this forum is just a place for pissing matches, that's really sad 😢. You all but called me a liar over something you obviously haven't tried and had no justification for your comments. The point is that yes you can see damage to an LD facet with basic things that all of us here likely have. I'm trying to be helpful here and add some value. Don't worry, i don't take it personally. I've been a member here for 11yrs, i know your type....troll. Now try to just have some fun, and happy lasing to you! 😁
 

Cyparagon

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You all but called me a liar
I said I doubted it. Don't over-react.

had no justification for your comments.
The fact that the emitting area is microns was justification for me to doubt. Unlike many others here, I'm happy to admit I'm wrong - that the damage area can be larger than I expected it would be. Thank you for proving otherwise, and thank you for showing a picture. Honestly!

You haven't answered my question. Was the damage on your diode because of back reflection or from something else like regular overdriving?
 
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Richie89

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back reflection for me unfortunately, I remember posting it here years ago but i had build an M462 back in 17 I believe. I was in an argument at the time with someone that I could crack a piece of clear glass with the laser focused to a hair. it in fact actually cracked the glass and you could slightly hear the high pitch "tink" noise as it broke. I tried to repeat the test and crack the glass again, this was before I knew how back reflection worked, I fired the 2W M462 back at the glass with my glasses on of course, and all the sudden my laser went super dim, I felt so stupid because I had no idea what I had done. I finally figured it out and hesitated to post if here, but I believe I did, I just don't know where I posted it at. ill see if I can dig it up. anyways, I felt stupid because I was 95% sure that's what had happened, instead of being wiser and shine it at an angle from the glass I fired head on. Laser went right back into the optics and through the diode window, especially with that kind of power their is no doubt it severely burned the diode.
 

Ramsey_innovations

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I said I doubted it. Don't over-react.



The fact that the emitting area is microns was justification for me to doubt. Unlike many others here, I'm happy to admit I'm wrong - that the damage area can be larger than I expected it would be. Thank you for proving otherwise, and thank you for showing a picture. Honestly!

You haven't answered my question. Was the damage on your diode because of back reflection or from something else like regular overdriving?
Thanks for your honesty. No hard feelings...

I don't know if that particular diode with the burnt spot was from back reflection but i strongly suspect it was. I do specifically remember decanning a 9mm 660nm that had back reflection cod and seeing the same type of damage/burn though. In my experience with the 650nm-660nm diodes if you over drive it to the point of failure it will either blow/lift the top gold layer on the semiconductor or vaporize a section of the bonding wire/s, thus causing an open circuit. I have also seen facets burnt do to overdriving but just not as often. Unfortunately I've killed more diodes than I'd like to mention... Usually if your overdriving a diode and it just stops working (doesn't go led), you have a chance (my record is about 50/50) at saving it if just a bonding wire blew. It's a pita of a soldering job to bridge the connection but if you have a REALLY steady hand it can be done. Just keep in mind that a soldering iron tip is gonna look like the size of a baseball bat next to that bonding wire under magnification and a slight flinch and it's all gone.
 




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