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Green laser dot issue

WeiHan

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Hey guys, I recently bought a green laser, a 150mw 520nm version. The beam is strong and powerful. However, whenever i shine the dot at a white wall, i will get something like this. The rectangle is not as bright as the dot, but it is noticable and really makes me annoyed. Its not the problem with the focusing ring, as the rectangle stays in the same position even when i turn the ring. However, it does change position when i rotate the whole laser, which makes me suspect its a diode issue. Anyone has any idea? Appreciate all help! Btw, greetings from Singapore!
 

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GSS

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It's pretty much normal to have a rectangular artifact as it comes from the diode die itself as annoying as it might be.
As you gave a drawing instead of a pic i'm assuming it's the artifact because every diode gives a rectangular spot profile when unfocused and we use different lenses to tame the spot to circular spot.
 

absolute

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It is not a defect, the rectangular artifact you see around the dot is a projection of reflections from within the diode package, which some diodes have.
 

WeiHan

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It's pretty much normal to have a rectangular artifact as it comes from the diode die itself as annoying as it might be.
As you gave a drawing instead of a pic i'm assuming it's the artifact because every diode gives a rectangular spot profile when unfocused and we use different lenses to tame the spot to circular spot.
Mine has this rectangular shape even when the laser is at its most focused spot, and it only occurs with my 520nm laser, but my 532nm or 445nm laser has no such issue. Is it normal? Btw, thanks for ur reply!
 

WeiHan

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It is not a defect, the rectangular artifact you see around the dot is a projection of reflections from within the diode package, which some diodes have.
This is the what i see when i unscrew the cap, does this particular diode have issue?
 

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GSS

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Pretty much. It's caused by that die behind the glass. 445's don't seem to show the artifact as much but i'm sure you see the rectangle spot when focusing it.
532's are DPSS laser's and use different setup and get the color through a set off crystals and a couple lenses. The initial diode is a 808nm and not visible.
 

DTR

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Here is a little dye reflection montage. The green is the most noticeable due to the higher relative brightness compared to blue and red colors that are available as direct diode lasers..

6551665515
6551465517
6550765511
6551265513
6551065509
 

WeiHan

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Here is a little dye reflection montage. The green is the most noticeable due to the higher relative brightness compared to blue and red colors that are available as direct diode lasers..

View attachment 65516View attachment 65515
View attachment 65514View attachment 65517
View attachment 65507View attachment 65511
View attachment 65512View attachment 65513
View attachment 65510View attachment 65509
Thanks so much for ur help! Is there any way to overcome this? Or is every 520 laser like this? All my previous lasers i haven't had any of such issues, or maybe they just aren't serious. What factors affects how visible/serious the rectangular spot is?
 

WeiHan

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Pretty much. It's caused by that die behind the glass. 445's don't seem to show the artifact as much but i'm sure you see the rectangle spot when focusing it.
532's are DPSS laser's and use different setup and get the color through a set off crystals and a couple lenses. The initial diode is a 808nm and not visible.
Oh okay thanks! Do all lasers have this issue? As in the 520s and 445s ? I feel like the one i'm experiencing is quite serious, the rectangle is very obvious
 

Immo1282

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You can't really do anything to the diode to stop it unfortunately. There may be an optics solution to minimise the appearance of it, but as others have said it's inherent to the diode. Be careful when you have the laser open as you did to take a picture of the diode itself. If dust settles on the diode window it may cause permanent damage to the glass when heated by the laser. Keep the lens on at all times if you can, and even better - keep a dust cap on the lens when it's not in use.

You probably did not notice this in a previous green laser - as it uses a different technology. 532nm lasers are DPSS or solid state - where an infra-red diode pumps a pair of crystals which absorb and re-emit the IR as green light. These won't display the rectangular artifacts, and generally produce far better dot roundness and narrower divergence. The lower-power 520nm diodes (PL520/B etc.) are not too bad compared to some of the more powerful ones avaliable.
 

WeiHan

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You can't really do anything to the diode to stop it unfortunately. You probably did not notice this in a previous green laser - as it uses a different technology. 532nm lasers are DPSS or solid state - where an infra-red diode pumps a pair of crystals which absorb and re-emit the IR as green light. These won't display the rectangular artifacts, and generally produce far better dot roundness and narrower divergence. The lower-power 520nm diodes (PL520/B etc.) are not too bad compared to some of the more powerful ones avaliable.
Ok thanks so much for replying! So, does it mean that the more powerful 520nm laser i have, the more obvious the rectangular artifact would be? It's not a quality issue right?
 

GSS

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Where did you get this laser and what kind is it by the way?
 

paul1598419

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This is the what i see when i unscrew the cap, does this particular diode have issue?
This is a Sharp diode and is listed as a 505nm, not 520nm. You can eliminate the artifact using the 520nm AR coated 2 element lens from DTR. Other lenses may also remove it. You might try the acrylic lens that comes with many modules as that has worked at times for me. Also, this diode tends to measure on the high side of the wavelength. A bit closer to 510nm.
 




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