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Messy Laser Spot on Sanwu Pocket

greggers

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Hello, this is my first post on LPF!

I recently received my first Sanwu laser: a 100mW 492nm Pocket series. It took a month to arrive after I placed the order. I have heard and seen many amazing things about all of Sanwu's lasers, however unfortunately I feel a little disappointed. I was expecting the very best, but perhaps I'm being unreasonable for what can actually be created with $120. After all, this is Sanwu's cheapest laser (excluding the 304 hosts).

My main gripe is how messy the spot is when projecting the laser onto a wall. Previously, I thought my $10 Laser 303 collection was poor, but these laser dots are much better next to the Pocket laser.

Additionally, something you can see on the paper becomes rather distracting outside. The two "cheeks" that spill out from the lens. I have a feeling this could be caused by reflections on the shiny metal inside edge of the aperture. Does anyone have a fix for this issue? It's driving me crazy. It is very visible outside. My first thought is to try and coat the inside edge of the aperture with matte black paint, I might try experimenting with this later on. (Just to be clear with the photos, the cyan laser is spilling light onto the grass, it is not an artefact created by the camera lens. The lasers in comparison are ~50mW red and green 303s)

Finally, the laser dot has a little box on one side. This appears on the opposite side of the dot to where the flat part is in the laser diode, if you know what I mean. Therefore I expect this is due to some kind of inherent diffraction from the laser diode itself, and is difficult to eliminate with the optic. Can anybody comment on that?

Thanks in advance for any replies to this thread!
 
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Ears and Eggs

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I have the Sanwu Pocket 60mW 488 and it does the same thing. I believe that it is caused by the beam hitting the shiny interior of the focusable end piece. Possible painting that a matte black might work.

Mine has a very similar pattern: See the 488 scatter above the second from left dot.

DSC-0734.jpg


sanwu488.jpg



It does seem to be a lot better, although not 100% gone, if you complete unscrew and remove the front collimating lens.

First picture here it is completely uncollimated, and second picture is collimated using a mirror lens from a camera.

sanwu4883.jpg


sanwu4882.jpg
 

julianthedragon

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Hi, I'm having trouble finding it but there was an answer on LPF to why the box effect happens sometimes with the cyan sharp diodes; if you want to dig, you might be able to find more through search. I own a 485-488nm small portable build by someone on LPF that does the same thing (I don't know who built it since it's passed through multiple hands). On top of that, I own a 520nm pocket from Sanwu with the "cheek" problem as well, so you could be dealing with multiple issues here. Contact Sanwu if you are very unsatisfied. The issue is something internal with the laser diode and optics. FWIW I also own a Sanwu 492nm Challenger II that does not have either issue, which might just be luck or a testament to getting what you pay for 🤷‍♂️
 

greggers

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Hi julianthedragon thanks for replying. I might contact Sanwu just to ask, but I feel it's going to be a few inherent faults with the design which are contributing to those issues - rather than a damaged optic or whatever else. After all, it is such a small host - that's probably where some of the corner-cutting (if it is) came from. As Ears and Eggs said, I believe the two spills are as a result of the machined surface of the inside edge of the aperture. Looking at the Challenger II you mentioned, I see the aperture edge could be a bit futher away from the lens, and also has a threaded section, so the same kind of reflection is unlikely. Since you also report this problem I wonder do all Sanwu Pockets do this?
 
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Ears and Eggs

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I just remembered that someone posted something similar about a year ago. This definitely looks like a design issue and not something wrong with your unit as there are now at least 3 examples of basically the same thing.


 

greggers

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Hi Ears and Eggs! I might try blackening several parts of the laser. Maybe I will even paint the inside around the diode. I will just have to be very careful not to get anything on the diode or lens, obviously.

Edit: just saw your most recent reply. I tried searching to see if anyone else had the issue but couldn't find any results! Thanks for letting me know.
 

julianthedragon

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Since you also report this problem I wonder do all Sanwu Pockets do this?

Greg
I’ll test my 200mw 405nm pocket, which is my only other sanwu laser. As far as memory goes it has a clean dot however it is 405nm and I wear goggles for any close range use so it’s possible I’ve never noticed

Might be something that “chunkier” multimode profile beams like that of 520 and 488 are more prone to
 

Ears and Eggs

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I’ll test my 200mw 405nm pocket, which is my only other sanwu laser. As far as memory goes it has a clean dot however it is 405nm and I wear goggles for any close range use so it’s possible I’ve never noticed

Might be something that “chunkier” multimode profile beams like that of 520 and 488 are more prone to


That would be my guess too. It's probably a combination of a specific host aperture design, plus a specific diode beam profile that causes it. So it might not even effect all the Sanwu pocket models. I unfortunately do not have any other Sanwu pockets to test, but none of the other lasers I own, including the two other non-Sanwu 488 pens, do not the same thing.
 
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Bingo. The issue is that the lens and diode combination causes this, though in this case, the sharp 488 will do this with just about any lens. The raw diode output diverges at a rate that causes it to clip at the focal length of the lens.

You can try swapping lenses, however the cap on the pocket is what holds it in place and really limits you to pretty much only the same FL. If I recall, they are using a 3E lens in the pocket. The G3 will be the easiest but still will leave small traces of what youre seeing, but if you want to completely remove the artifacts you can get a G8 and shorten the barrel (I've done this with a dremel).

Ignore the artifacts closest to the spot, those are from a spring holding the lens in place. From left to right, 2E green lens, 3E lens, g8, g3, acrylic.

Ideally, you'd have a longer distance from the lens and the aperture to mask the clipped reflections, but the host just has the lens sit too close to the aperture for that.

As for the box reflection, the g3 or g8 will tame that a bit, but it's a lot harder to get rid of. That is an issue with Sharp's diode manufacturing process, you're gonna have it in some capacity as long as you're using their diode. Osram makes 488s as well, but be prepared to shell out $1000 or so for one
 
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greggers

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You can try swapping lenses, however the cap on the pocket is what holds it in place and really limits you to pretty much only the same FL. If I recall, they are using a 3E lens in the pocket. The G3 will be the easiest but still will leave small traces of what youre seeing, but if you want to completely remove the artifacts you can get a G8 and shorten the barrel (I've done this with a dremel).
Thanks for the insight ZRaffleticket! As this is my first "serious" laser I think I'll leave it as-is for now. I would like to experiment with different lenses in future, though; I'll bear what you say in mind!
 

Ears and Eggs

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Took a couple pictures to compare it with my other ~60mW 488 that comes in this blue colored pen host. It doesn't seem to have this issue at all with a much cleaner dot:


First is the Sanwu Pocket 60mW

4881.jpg


Second is the other 60mW 488. Not sure what company makes these as I got this unit as part of a group buy on a discord channel:

4882.jpg


The business ends of the two units for comparison:

4883.jpg
 
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Yep because the lens sits further back inside the host - it is still happening but the host itself is blocking that stray light from coming out the aperture. That's probably the best way to handle it, but isn't really an option on the pocket.
 
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I suppose you could try masking the aperture with black electrical tape. Haven't tried that but it might work.
 

greggers

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I suppose you could try masking the aperture with black electrical tape. Haven't tried that but it might work.
True! I may try, but also I don't really want to contaminate the lens (anywhere on the laser really) with the sticky adhesive. You know how electrical tape goes after a while...
 
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True! I may try, but also I don't really want to contaminate the lens (anywhere on the laser really) with the sticky adhesive. You know how electrical tape goes after a while...

Sure, there are other things you could use to mask this out though. The electrical tape I would use would go on the focus ring, so not likely to contaminate the lens. Yours doesn't seem to have a focus ring.
 




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