Old 10-25-2009, 05:31 PM #1
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Default Back Reflection question

So, I found a few posts regarding back reflection and possible internal damage.

My question is about the aperture being closed. Many portables (such as my RPL-400) have a small slider switch to block the aperture. I guess this is primarily to keep out dust when it's not in use. Is there any concern about power up and forgetting to open it? Someone is bound to have done that, but I couldn't find a reference.

Thanks!


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Old 10-25-2009, 05:46 PM #2
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Default Re: Back Reflection question

Quote:
Originally Posted by roosl View Post
So, I found a few posts regarding back reflection and possible internal damage.

My question is about the aperture being closed. Many portables (such as my RPL-400) have a small slider switch to block the aperture. I guess this is primarily to keep out dust when it's not in use. Is there any concern about power up and forgetting to open it? Someone is bound to have done that, but I couldn't find a reference.

Thanks!
Yes, of course. You could:

Get some reflections inside the diode even if the lid is black.
Burn the lid.
Overheat the module if you leave it on for too long.


Please take care of your RPL, they're damn fine lasers
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Old 10-25-2009, 06:25 PM #3
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Default Re: Back Reflection question

Those are the ugly scenarios I imagined Felt I should ask, so it'll be here!

Thanks again!
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Old 10-25-2009, 06:43 PM #4
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Default Re: Back Reflection question

I believe when it comes to DPSS lasers, the light converting crystals should protect against back reflections, while diode and lens setups(aixiz modules and the like)are really the ones that are most susceptible to this problem.
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Old 10-25-2009, 09:22 PM #5
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Default Re: Back Reflection question

You don't need to worry about reflections from the aperture shutter.
1. It is a matte black metal surface... the beam will be scattered and absorbed.
2. The length of the cavity and the narrow path the beam must travel through will not allow much reflected light to get through.
3. Also, the crystal coatings will block any reflected green light from reaching the diode.

The shutter was designed to block the output. There is nothing wrong with powering it on with the shutter closed.

You only need to worry about reflections when you are dealing with diode lasers. Using AR coated lenses will minimize reflections. If the wrong wavelength coating is used, or no coating, a percentage of the beam will be reflected back to the die. This puts the diode under more stress and can cause the delicate emitter to deteriorate.

I've never lost a diode to reflections, though... so I'm not even sure the reflected light is enough to really cause much damage in most cases.
I would imagine laser diodes outputting >600mW would be more susceptible to this since even a small percentage of reflected light is quite a bit.

Last edited by RA_pierce; 10-25-2009 at 09:25 PM.
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Old 10-25-2009, 09:31 PM #6
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Default Re: Back Reflection question

Quote:
Originally Posted by RA_pierce View Post
I've never lost a diode to reflections, though... so I'm not even sure the reflected light is enough to really cause much damage in most cases.
I've lost a LOC and a 1W 9mm this way
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Old 10-25-2009, 09:40 PM #7
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Default Re: Back Reflection question

Excellent info, all. Hopefully other noobs will find this helpful, and now I can stop doing that double-take-OMG*sigh* when I power on, in case I do forget to open it.
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Old 10-27-2009, 02:26 AM #8
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Default Re: Back Reflection question

I was doing this (using a ND filter) and didn't even think about this effect.
Thanks for the heads up.
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