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405nm Dot, Interference pattern?

Exerd

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Jan 2, 2010
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I was using my glasses to observe the dot output of my 12X 405nm laser I made a few years ago. I noticed an interference pattern of bullseye rings within the dot at about 2 meters. At one point, I may have changed the lens. I can't remember fully if I pulled the G1 lens, but I'm thinking that this might be the module I glued an Aixiz lens into. At the time I focused the beam at distant trees, when I thought I had the best beam collimation I could achieve I glued the lens in place (not directly, but from turning the barrel threads).

I thought I observed this dot before, with glasses, and don't recall this dot-ring pattern being there--it was smooth and intense closer the center as a gradient. This may have been with the other G1 lens, though, and this lens *could* be the Aixiz 445nm version (slightly golden coating).

Is the lens possibly not in the best focus, and causing some sort of interference pattern from refraction of sort? Or could the Aixiz 445 lens simply not work well with this diode and the pattern will be there no matter what?

A picture says a thousand words (well, an interpretation of what I see anyways. Near exactly what I see):

wpIEQYP.png


Thoughts? Seen this pattern before?
 



Exerd

Active member
Joined
Jan 2, 2010
Messages
448
Points
28
You hit that nail on the head! Except, I cannot rep you. I need to "pass more around first". ;)

Wiki images show a duplicate of the beam, the center photo column, top and bottom pictures, look exactly like the dot now that I've looked again, the point at the center is dense, and the outside rings have larger gaps that fade away just like the two images on the grid:
800px-Spherical-aberration-disk.jpg


I bet I am using an Aixiz 445nm lens (they came out early on, with 445nm projector diodes a few years back when the A140s first poured in).

As I recall, the G1 lens has more of a bluish coating, right? This lens I have, definitely has a more golden coating. My guess now, is that the FL/aperture is suited to the 445 wide beam pattern, and the G1 is maybe a slightly shorter BFL.

Does anyone know the specs off the top of their head of the G1 lens FL? Such as its FL, vs a FL that would likely be used with a larger chip diode, like the multi-mode 445nm A140s?

I'm guessing the larger multi-mode die would call for a slightly shorter FL, to aperture the wider beam fully without losing too much light. Or, maybe I have that reversed, and they use a longer FL in the 445nm specific lens to try and keep divergence lower (while giving up some light that won't actually aperture). Then, the 405nm could use a shorter FL in the G1 in that case, which inherently will have better collimation due to the much smaller lasing die area. Just guesses here. :thinking:

I will play with focus, and break the glue seal. I'll see if I can correct the problem first just by FL adjustment. Then I will compare against the G1 to see if this problem occurs in both lenses as easily.
 




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