Old 08-31-2010, 08:58 AM #1
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Default Backreflection protection

Yeah, 'tis me again. I don't get paid enough to be the random link bandit so I just post threads instead.

I was screwing around with a 1mW pointer, and I've found something that may be of some use for anyone who's had a build killed by a reflection into the diode.

Needless to say it involved a 1mW red pointer, the tip of a green module, and a dichroic mirror/splitter from a DVD player (for red builds) or from a blu-ray drive (for violet builds).

These dichros are odd things- unlike normal dichros or beamsplitters, the amount of light they pass or reflect is entirely dependant on their polarisation and their orientation to the beam.

The end result is that if positioned correctly, you can have the dichro pass all light while preventing reflections from entering.

Here's the modified pointer in question (1mW red, 650nm), and two pictures how it all works.



See how the reflection forms a square on the card? The reflections are no longer coherent, but it shows it works.





I've tried shining a 5mW module into the pointer through the dichro, nothing.

The splash behind the dichro is not a result of the dichro- it was there before the dichro was installed. The original purpose of it was to cut down on beam splash. That didn't work, the beam profile still looks terribad (the spot at 5m is disgusting), but it's now safe from reflections, but I'm not too sure how that helps.

Be VERY careful when testing out the dichro- you wouldn't want to kill it with a backbounce, now would you? The irony alone would probably be enough to kill the diode.


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Old 08-31-2010, 12:24 PM #2
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Default Re: Backreflection protection

So what extactly is this optic you mounted to it?

One thing that comes in mind as a reflection protective system would be a 45 degree polarization modifier, making more or less and optical diode.
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Old 08-31-2010, 12:31 PM #3
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Default Re: Backreflection protection

It's an optic from a DVD burner, and it;'s the one that's 1.5mm thick, with the blue-red(depending on angle) coating.

Harvest the diode, and harvest that little overlooked scrap of glass. It just could save your diode.
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