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Replacing a blown 808nm diode in a green module

skjult

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I have an approx 150mw green module which has a blown diode and / or driver board. Wanting to do 1 of 2 things:

1. Replace 808nm diode and driver with new ones at same level of output. Cheap.

2. Replace both with a higher output combo. Still cheap.

I have heard that the crystal will generally not take too much more than designed... and that this is partially (maybe wholly?) the reason the big mW greens are expensive. Big output 808nm does not seem to be much of an issue.

Thanks in advance.
 



AnthoT

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It's hard to tell actually, if you have an LPM you should meter your existing one to get an idea of what you need to change it :)
 

skjult

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Problem there is it is blown, so no way to measure. Though I believe it was around 150mW. How much was IR, dunno. It did burn pretty easily and was quite a bright green.
 

skjult

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Here is the 808nm diode pulled from the module. It's a nice module, so I'd love to rebuild it! I'll definitely post info about the process here. I will post some pics of the (possibly blown) driver. I will test it later. Need to build a dummy load first. This diode is canless (does it matter?) and was held in place by a screw-in retaining ring. Like I said, nice unit. My guess is the diode is a 300 or 500mw. I'd like to put the most I can in there and use an appropriate driver to ramp it up to what the crystal will sustain.

One concern: the crystal - if too much IR is pumped into it, what is the outcome? Will it just be obvious no more green light is produced or will the crystal be destroyed?

Thanks!
 

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ElektroFreak

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There are two major concerns when changing out diodes:

1) The 808nm diode's wavelength should be as close to 808nm as possible. Many diodes are rated at +-5 to 10nm, which is a lot of variation. Better diodes are rated at +-3nm. I'd recommend using an 808 +-3nm diode. The others often work, but peak efficiency (and thus output) is achieved with as close to 808nm as possible.

2) The orientation of the replacement diode must be the same as the original unless you want to have to do a lot of other aligning. Whenever I swap pump diodes I mark the position of the dead diode so that the replacement goes in as close as possible. You'll still have to adjust a bit, but marking before removing the old diode usually saves a bunch of time and effort.

Regarding the effects of overpumping the crystals, usually they can handle a pretty good amount of pump power, but it is possible to burn the coating of the crystal. These coatings act as mirrors at certain wavelengths and anti-reflection at other wavelengths. If the coatings are damaged, it will severely effect the performance of the laser. You'd need to either reorient the crystals so that the pump beam enters in an undamaged area of the crystal surface, or (and this is by far the preferred method) replace the crystal completely.
 
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RA_pierce

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To add on to what EF said...

More pump power does not always mean more output power even if the crystals are not damaged by heat.

Once the crystals are saturated, the pump to output efficiency will start to drop off. At some point you will get less and less power out as you continue to increase the input power. Eventually the power may start to drop off as the temperature continues to rise with the excess pump power or you will get mode shifting.

BTW, If the module was rated for 150mW the pump diode is probably 500mW.
 

skjult

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Any recommendations on an inexpensive 1W class 808nm diode? I can't find anything in a TO18 package. Looks like the highest is a 500mW...

808nm 500mW Laser Diode / TO18 (5.6mm) 1 PCS | eBay

This one is $19 and looks to have good specs...

500mW 808nm Infrared laser diode/TO-18(

300mW TO18 are far cheaper - this one is $4...

808nm 300mW 10*6mm High Power Burning IR Infrared Laser Diode Module 3 Pins Lab | eBay

The one I removed is canless. Is this important? Is it possible to pop the can off. Well, sure, it's possible - but is it recommended?

Yeah, unfortunately I pulled the diode before marking how it was in. But I'd guess that moving it through 360 degrees and noting the visible output ought be a quick and dirty way to do it. Perhaps at a lower power level.

Thanks!
 

skjult

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Here is the driver I pulled. I haven't tested it to see whether it is it or the diode (or both) which are blown. Initially when it failed, it would get hot with no visible output. Then it just was cold.
 

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billg519

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You would be best to replace both the diode and driver in your dead module. The diode you posted pics of shows three connection pins and a photodiode (for optical feddback to the driver) is visible. Were all three pins connected to the existing driver? If so, then you would be best to change both the diode and driver because its hard to know if a different diodes photodiode would give correct feedback. It is possible to de-can a new diode, but this can be risky. It might be better to find a diode with no can, but these can be rare. I hope that you can get the alignment back once you have a working driver/diode pair to begin testing with. This can be a fun project and a good learning experience. At worst, the green won't work, but you will have the driver and diode to make an IR burner. If your green module was 150mW, very likely it uses a 500mW 808nm diode. 300mW would be too little input to the crystals.
 

skjult

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Here's the module. Compared to some of the cheapies I've seen, it strikes me as rather nice.

About the 500mW diode - is it possible to drive these beyond their max ratings and achieve any benefit?
 

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billg519

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That is a very nicely made green module. Quite a shame that it croaked. If you want to get into creatively overdriving laser diodes, you really need an LPM (laser power meter). You need to increase the current to the diode while monitoring laser output. There is no point increasing current if laser power is not going up as well. You will just heat and burn the diode. Around the forums here, we tend to drive diodes well beyond what the manufacturer often intended and there can be benefits for doing this. You need to be able to do the measurements though, or you will risk blowing diodes.
 

skjult

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OK - thanks. Until I get an LPM, I'll set it per manufacturer ratings.

I was looking at the $69 J.Bauer meter, but it runs to 200mW. Led me to wonder if one could use filters to attenuate the beam to some predictable (and linear) rate. My guess is such optics would end up costing as much or more than a meter that can handle 1W +.
 

billg519

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You can get a very good LPM here on the forum. We have members that make them. The "Laserbee" meter is a well known and reliable meter. I've had one for a couple of years. The Kenometers are good too. That J Bauer just doesn't go high enough and as you said, barring a super deal on (proper) optics, it could be costly. The Laserbee and Kenometer are thermal LPMs, so you don't have to worry about the laser frequency. My Coherent Lasercheck is a photodiode based meter and I need to know the exact nm's of the laser to be measured if I want an accurate reading from it. The J Bauer might be a photodiode unit too.
 




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