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I killed 2 Maxys at the same time by rotating a test mirror mounted on a screw..
D'oh -- aint gonna do that again.. now I got a firmly planted output mirror that doesnt rotate.. until I get my galvos..
Then gonna be real careful still.. DI arent forgiving like dpss..
Damn... :eek: I didn't know there were that many dead Maxyz around. Is there anyway to protect them from this? :confused:
Yeah - don't reflect the beam back into the diode! :D Seriously though, while you're setting up the table and aligning everything it's smart to run all the lasers at low power. When I did my alignment I was running less than 1.5 volts to the analog rails of the lasers. This also makes alignment easier because the specular reflections from the optical components are quite dim at that low power so you can easily see where the beams are landing on the optics. With the power cranked up I find that the specular reflections are so bright I have trouble even looking at the dichros, much less trying to verify that the beams are overlapping.
Adam
You got my full sympathy there. I remember when I first discovered retroreflection death. I'd just paid £530 for TEN diodes, they cost so much then that's all I got for my money, and they were only 80 mW too. It's why I never really followed through on my designs. I'd destroyed nearly HALF of those diodes before I'd established that retroreflection death was a real phenomenon, there was nothing in the LaserFAQ about this, and the makers and sellers of the diodes certainly weren't telling anyone. I had to push for weeks to even get them to admit it. (The seller was much more helpful than the maker though).Quote:
Originally Posted by steve-o
I won't be building anything grand, I decided. Not worth it. No-one will pay for the engineering required to make a red laser be able to change diodes easily like projector lamps, it would cost far too much money to do it, and it's why no-one with any commercial sense does it. The nearest to that is to charge money to refit a laser already sold. I've considered that too, as Marconi does, but ruled out building entirely, as I discovered I can get more money far more easily just selling diodes! As I have more diodes than I can use, and far less money than I need to finance laser building properly, I'm doing that. What that leads to I don't know. Maybe an FB3. If people DO decide it's worth paying serious money for designs that allow easy refit of diodes, I might build some, but I doubt it, to make it truly EASY to get the same kind of alignment and thermal coupling and avoid easy contamination of clean parts would be so difficult it will never be something for the casual end user, and it could drive the price up tenfold unless you had a serious commercial machine shop already owned and in your own pocket. It would be like the difference between a bit of DIY metalwork and a set of finest Newport optics mounts.
How does he know this? Can it be proven??Quote:
Originally Posted by Laser Ben
Yes...
ALL Red diodes can be destroyed from back-reflection
I have not found one that couldnt..
You must be very careful during alignment or just playing around as it
is very easy to reflect some light back in an destroy the diode.
It is very unlikely that the diode will just die.. but that does happen too.
But we cant rule out static discharges and improper focusing techniques.
In returns that we get, It is very hard to tell if back-reflection actually was the cause of the damage.. thats why we use a very expensive microscope.
That way we can see if the facet was damaged.
Since we do not have a warranty on them because of the low price and because of the nature of laser devices and their use-
We must charge for a diode refit after a unit has been out in the field for some time..its just cheaper that way.
Otherwise the prices would be double to justify a warranty.
Thanks for reply. I have various diodes here that have been killed and a microscope. What do I look for to see if back reflection has seen them off or if something else has done it?
Well, There are several indicators of damage.
Either the facet face or a fracture in the die.
The face is easy to see in a microscope.. but the die takes a bit more to see.
Since the diode is basically dead. and we dont want to fire it up directly,
Sometimes we have to excite the die by an external light source (another laser) to see the damage.
Since this would take up a lot of time trying to explain.. I'll make this short.
I think a read in Sams laserfaq and maybe some googling may be in order since this has been done already.
For those who might be interested http://www.laser-diodes.net/techinfo...mg_prevent.pdf
has some typical senarios of how some diodes were damaged and what they think damaged them.
The example in section 5.2 is prettymuch how we look at diodes.
But the short of it is, this mostly shows up as measles on the output face of the facet or abnormalties in the active layer.
But it still is very hard to know whether the damage was optical overload or electrical without evaluation. This is a study in itself.
There is tons of info on the internet about this.
Of course you could purposely damage some diodes in different ways by expermentation an see the results.
But that could get expensive...
Thanks for that. The other problem I'd have dissecting them is that I've had to remove them from the lens and the only way I could do this is by tapping the diode back out from inside the lens so probably did it more damage anyway.
Actually, there is a section of Sam's Laser FAQ that addresses this problem, though it's not labeled as "back reflection" per se. Still, if you read through the FAQ from start to finish, you'll find the above passage that talks about power changes in a pointer diode when the beam is reflected back onto the face of the diode. They also mention catastrophic failure due to over-power at the face in that section, and they warn you about back-reflection.Quote:
Originally Posted by The_Doctor
I often pick random sections of the FAQ and just start reading when I'm bored at work. (I've kept an up-to-date copy of the FAQ on my hard drive for the last 5-6 years or so, both at work and at home, and I'm *still* finding cool things in there.) It's amazing how many useful nuggets of information are buried inside some of the more mundane topic headings.
I agree that most diode manufacturers won't warn you in advance of the danger inherent in back-reflection, however.
Adam