What causes light leakage?

[lasergal]

Forgive me for creating a new thread on a subject that I'm sure I've read about here before, but I did a search and came up empty on the subject.

What causes some cheap pointers to leak light? I mean visible laser light that appears in places other than just the beam and/or dot. I've seen a few of these- especially in dollar store type pointers.

Is it due to inferior lenses, or improper placement of lenses, defective or inferior diodes, or something else?

And finally, is there any easy, inexpensive way to correct this? Obviously if the pointer was inexpensive, I don't want to spend a lot of money to try and fix it.

Not really an important issue, but I would like to know what's going on.

 

[ARG]

Can be caused by poor optics, bad diodes and dirty lens' but it is most likely a speckle pattern.
Speckle pattern - Wikipedia, the free encyclopedia

 

[lasergal]

Can be caused by poor optics, bad diodes and dirty lens' but it is most likely a speckle pattern.
Speckle pattern - Wikipedia, the free encyclopedia

Thanks for your answer. I already knew about speckle, and this is something else entirely. For example, one keychain laser I have throws light on the floor, well below the beam. I have another one that shows a faint ring of light around the dot. The better quality ones do not do this.

 

[Marco Polo]

All of my lasers have a 'halo' pattern surrounding the beam. If you rotate the focusing lens, the lens scatter will rotate with it. Even lenses in good condition throw some amount of halo.

Anything that doesn't rotate with the lens is either a reflection inside the module or diode, something on the diode window, or else stray emissions from the diode facet. Maybe diffraction/interference artifacts too. The Osram PL520 and PL450 have a pronounced squarish facet artifact.

 

[DrSid]

You have to keep all lens surface clean. That also applies for crystal and output coupler surfaces, and for filters. And by clean I mean totally clean. With lasers, single grain of dust can ruin the beam. Lasers are actually pretty good for measuring how clean your optics are.

 

[jander6442]

I know a good joke or even a heavy sneeze causes me to have a light leakage.:yabbem::na:

edit: or lite leakage.

 

[Blackwolf]

Also if you have a three element lens you will get some internal reflections. My 445 dot looks like this, ( - ) but the outside splashes are very weak and can only be seen in heavy fog.

 

[lasergal]

Yeah, one in particular throws A LOT of light at the floor, or other places it's not supposed to. I'm thinking "stray emissions" best describes it, but am clueless on how to correct the problem.

The lenses shouldn't be dirty since it's brand new.

 

[DrSid]

Brand new has nothing to do with. Transportation is perfect time for dust to get there. It might have been there since manufacture. Maybe post a picture .. we can usually tell if it's dust or reflection, also lens dust looks different then diode window dust (not applicable with green lasers), and so on.

 

[BShanahan14rulz]

Poorly designed lasers may have an aperture that is smaller than the beam. Light hits the sides of the exit hole and bounces off in a crazy direction. Maybe you can somehow widen the hole or remove the aperture entirely to see if that is the problem.