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spot beside the dot

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originalbigT

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Oct 1, 2008
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Hey guys, I've been searching the forum for awhile and couldn't find anything like this. I have an open can red laser build that I just finished. It was working fine with a really clean visible beam. For some reason there is a sperate beam coming out. It makes a big blob beside the dot and can itself be focused to a line. I checked for debris around the diode and the lense. Nothing. I tried to blow it out but i don't want to damage the crystal. Is this a mode shift or a warping crystal? Thanks guys.
 

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joshshermannn1

joshshermannn1

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Green lasers usually mode shift, i've never seen a red one do it though. IIRC, Red lasers don't have crystals unless they're DPSS lasers; Green lasers typically use crystals to get their wavelength through a process called frequency doubling. Could you post pictures of the lens and diode?
 
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originalbigT

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Thanks for the info, I assumed the diode itself had a crystal in it. I'm actually on another tab researching how these diodes work. Unfortunately I can't get a pic of the diode in the housing. It's an open can out of a lg dvd burner. It's pressed into an axis module. If it dies I won't be too concerned, as a machinist i just used it to help make a host for my pending 445 build, still, it's always nice to have a strong red in the family. Thanks again, I appreciate it!! +1 for taking time to help
 
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originalbigT

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It is a 638nm. I never noticed this before, it doesn't seem as bright to me anymore either. But that could just be me being paranoid. That makes me feel better knowing yours is ok like this. How long have you had yours?
 
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Lethere Belight

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May 20, 2012
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Had it for about 6 months. Wanted a strong red one at hte time. Don't think I would have gotten it if I would have known.
(It actually said something in the description about it but I didn't notice)
The beam is not bad but I don't like the "dot".
 
RA_pierce

RA_pierce

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A DVD burner diode you say?

Those diodes are usually 655-660nm, not 638.
Either one should not produce 2 beams.

Take off the lens and shine the beam on the wall.
Here is an example of what a clean laser diode looks like...

The laser shown here is a 20mW 635nm diode and has an elongated profile. The laser you have should produce a similar profile only more circular than elliptical. Unfortunately, I don't have a pic of the profile of a diode more like the one you have.

If the "raw" output looks normal, then it is probably something wrong with the lens.
 
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originalbigT

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She died today. I'm going to use the host and heatsink for my 445 when it arrives. Thanks RA_pierce for the help man. I appreciate it.
 
Cyparagon

Cyparagon

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The diode IS a crystal. But crystal is a pretty broad term. Table salt is a crystal, too.

The second beam is likely an internal reflection in the lens. DVD diodes don't mode hop.
 
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