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Finding max mw for an Open Can LD

Zarniwoop

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I've got an "Open Can" LD that came from an 18x drive.  Been using it recklessly in a MagLite with no protection whatsoever.  I'm planning to pull it out of there and use Daedal's regulator circuit, but I'm wondering...  How does anybody find the max current for their diode without having two and blowing one first?
Does anybody have a spec-sheet for an open-can diode?  (That's hard to search for on Google.)  I suspect they'll tolerate more than 3V, and I don't know how much current.
I don't really want to turn up the current till the brightness seems to plateau, because that's almost certainly going to damage it. On the other hand, if I go really conservative, maybe I'm only getting half power.
Thoughts anybody?
:-/
 



Gazoo

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The open cans are awesome. I have run mine as high as 500ma's by accident...lol. Normally I run it around 250ma's but on "special" occasions, like when I want to burn a hole through a floppy, I will run it at 350ma's.

I have had it for two months and it is a killer. Now keep in mind I am cooling it with a peltier, .......you should be able to do the same, but keep the duty cycles really short when running above 250 ma's. It does heat up quickly.
 

o_DEATH_ANG3L_o

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Yeah I am really thinking of pulling the one out my Liteon. I hear they burn really awesome. Well I'll let you guys know the results when I work the courage up to harvest it. ;)
 

justin07

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they may be tough for current but flying across the room and smacking the wall seems to kill them instantly ;D
 

Hemlock_Mike

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Uh - Justin ----

I only do that AFTER I hit 'em with over an amp of current ;D :D :'(

I've posted here many times on how to approach the limit on an LD.

Mike
 

Ashton

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This is a really dumb question... but is ther really a limit? if you could cool it adequatly, couldn't you runa diode @ > 500ma? or at >3v? now, I'm talking about something like submerging it in liquid nitrogen cooling, couldn't you run it as high as you wanted to as long as it stayed cool?
 

pullbangdead

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Ashton said:
This is a really dumb question... but is ther really a limit? if you could cool it adequatly, couldn't you runa diode @ > 500ma? or at >3v? now, I'm talking about something like submerging it in liquid nitrogen cooling, couldn't you run it as high as you wanted to as long as it stayed cool?
Well, think about it this way...how does a laser diode really work? What is the mechanism that allows/makes electrons fall back through a potential and emit a photon of very specific energy? What is the mechanism of how the electron was excited up to its high potential in the first place? Laser is "light amplification by stimulated emission of radiation", what is stimulated emission, and why does that amplify light? Once you know these mechanisms, what limits these mechanisms, or inhibits them from being infinite? Is it purely temperature? These are all things you can find out, and with some thought and research of course. But for your effort, you'll have a very deep understanding of what is simultaneously one of the most advanced and one of the most fun pieces of technology to come out in recent years (talking about laser diodes in general).

Sorry, I know that's probably not what you're looking for, but I've learned from people and have become a person who really values the discovery part of all this. Sure, someone can tell you "yes, that's true", or "no, it won't work", but then what have you gained, and should you really believe them if you don't know yourself? And besides, all these semiconductor systems are amazing things that are worth learning about all by themselves. Lasers are making all this communication and really most of the communication going on today actually happen, it's good to know why they work.

</preaching on the academic merits of learning>

BUT, if you really don't care, I or someone else can just tell you.
 

Ashton

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BUT, if you really don't care, I or someone else can just tell you.
LOL!!! Love the ending!

I'm alredy crammign my furry little skull full of mostly-useless computer and IT information, since that's my major, I'm not very advanced in physics yet, I tried to read the post somewhere about about how lasers work and I got a hedache... I'm fairly sure my hypothesis is incorrect about lasers basec on teh fact that if you do the same trick with a comptuer CPU, it still shortens it's lifespan, even if it IS super-cooled because the cercuitry jsut wears out faster being used more. Nothing non-biological lasts longer hte more you use it. I assume you could run it at any power nearly but you would end up with a single pulse before it died.
 

pullbangdead

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Ashton said:
BUT, if you really don't care, I or someone else can just tell you.
LOL!!! Love the ending!

I'm already cramming my furry little skull full of mostly-useless computer and IT information, since that's my major, I'm not very advanced in physics yet, I tried to read the post somewhere about about how lasers work and I got a headache... I'm fairly sure my hypothesis is incorrect about lasers based on the fact that if you do the same trick with a computer CPU, it still shortens it's lifespan, even if it IS super-cooled because the circuitry just wears out faster being used more. Nothing non-biological lasts longer the more you use it. I assume you could run it at any power nearly but you would end up with a single pulse before it died.
Well, at the semiconductor/material level, to fully understand the inner workings, it's more complicated than what can be described here. The applied voltage, to put it simply, provides a bias/energy to raise the electrons to a higher energy level in the system. In a laser, this actually changes the energy bands of the materials (there are multiple layers with different materials in the diode, it's usually a double heterostructure, so there are 3 layers), allowing the electrons to move from one material to another. This voltage just supplies the energy needed to make this happen by lowering potential barriers, so extra voltage is of no good typically, so all extra voltage will do is break things. (Although, a lower temperature will also change these potential barriers in the material, so more or less voltage may be needed, but I'd have to actually stop and think about that for a minute). Once the electrons are in the active layer, there exists a "population inversion" in the active layer. This basically means that under these conditions, there is always a hole in the valence band for an electron in the conduction band to fall back into. The electrons will spontaneously fall, and emit a photon of light corresponding to the band gap (kind of like an LED). However, there will be a time before the electrons fall. This is where lasing comes in: photons previously emitted with the same energy/wavelength pass by, and Stimulate an electron to fall and emit a photon. This new photon will be coherent with the photon that stimulated its emission. Thus, the optics that make the photons bounce back and fourth before being emitted, resulting in amplification of the light (a laser without the optics is simply a light amplifier). A new electron will replace the fallen electron in the conduction band of the active layer, and the process repeats.

As far as current itself, more electrons in the active layer means more electrons to fall through the potential barrier, means more electrons stimulated by photons, which means more photons, so power increases VERY rapidly with current. But, from what I've read, the main mode of failure for an LD is the "COD" that others have mentioned elsewhere. This is a function of too much power damaging the optics and mirrors that are required for lasing to occur. So, unless cooling makes the optics less susceptible to damage, I don't think it will help at all. The light amplification and emission might become more efficient, but without the optics you can't get the stimulated emission that makes it all work.

I could go into greater detail, but that would require more semiconductor and device theory than you probably know.
 

Ashton

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That is a WONDERFUL explanation! Thanks for hte insight! Now I do fully understand the basic principals of how a laser works!

AFAIK the only way the cooling helps is that the process generates heat which CAN damage the reaction chamber and optics, so once you overcome the heat any additional coolish would be worthless and could even be detrimental depending on the materials and how they react to low temparatures (I know some materials will warp and crack once the temparature is low enough, though I'm not familiar with the ones in a laser diode)

Thank you again! you gave me an answer that left me >100% satisfied!
 

Things

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ya they can get so hot they melt their own internal mirrors! ;D ;D ;D ;D
 

Daedal

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pullbangdead said:
[quote author=Ashton link=1190257153/0#7 date=1190476430]
BUT, if you really don't care, I or someone else can just tell you.
LOL!!! Love the ending!

I'm already cramming my furry little skull full of mostly-useless computer and IT information, since that's my major, I'm not very advanced in physics yet, I tried to read the post somewhere about about how lasers work and I got a headache... I'm fairly sure my hypothesis is incorrect about lasers based on the fact that if you do the same trick with a computer CPU, it still shortens it's lifespan, even if it IS super-cooled because the circuitry just wears out faster being used more. Nothing non-biological lasts longer the more you use it. I assume you could run it at any power nearly but you would end up with a single pulse before it died.
Well, at the semiconductor/material level, to fully understand the inner workings, it's more complicated than what can be described here. The applied voltage, to put it simply, provides a bias/energy to raise the electrons to a higher energy level in the system. In a laser, this actually changes the energy bands of the materials (there are multiple layers with different materials in the diode, it's usually a double heterostructure, so there are 3 layers), allowing the electrons to move from one material to another. This voltage just supplies the energy needed to make this happen by lowering potential barriers, so extra voltage is of no good typically, so all extra voltage will do is break things. (Although, a lower temperature will also change these potential barriers in the material, so more or less voltage may be needed, but I'd have to actually stop and think about that for a minute). Once the electrons are in the active layer, there exists a "population inversion" in the active layer. This basically means that under these conditions, there is always a hole in the valence band for an electron in the conduction band to fall back into. The electrons will spontaneously fall, and emit a photon of light corresponding to the band gap (kind of like an LED). However, there will be a time before the electrons fall. This is where lasing comes in: photons previously emitted with the same energy/wavelength pass by, and Stimulate an electron to fall and emit a photon. This new photon will be coherent with the photon that stimulated its emission. Thus, the optics that make the photons bounce back and fourth before being emitted, resulting in amplification of the light (a laser without the optics is simply a light amplifier). A new electron will replace the fallen electron in the conduction band of the active layer, and the process repeats.

As far as current itself, more electrons in the active layer means more electrons to fall through the potential barrier, means more electrons stimulated by photons, which means more photons, so power increases VERY rapidly with current. But, from what I've read, the main mode of failure for an LD is the "COD" that others have mentioned elsewhere. This is a function of too much power damaging the optics and mirrors that are required for lasing to occur. So, unless cooling makes the optics less susceptible to damage, I don't think it will help at all. The light amplification and emission might become more efficient, but without the optics you can't get the stimulated emission that makes it all work.

I could go into greater detail, but that would require more semiconductor and device theory than you probably know. [/quote]

You hit it right on the nose! :) Nice to see a fellow engineer on board... :D Good to see you paid attention in your Semiconductors class ;) :p (I had to as well... my professor was, let just say, difficult ::))

--DDL
 

Daedal

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things said:
ya they can get so hot they melt their own internal mirrors! ;D ;D ;D ;D
COD... Catastrophic Optical Damage... funny how it also works with Cause Of Death... ;D

--DDL
 




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