Laser pointer patterns?

[nikosb]

I have a cheap 5MW green laser that. When I adjust the lens at the front by screwing it in or out the laser beam diameter becomes smaller or larger. When the beam is spread out I notice that the beam is not uniform, it contains round patches and there are radial patterns as well as show in this image:

Why does this happen? Is this an issue with the the lens or is it an issue with the quality of the laser?

 

[Pi R Squared]

I have a cheap 5MW green laser that. When I adjust the lens at the front by screwing it in or out the laser beam diameter becomes smaller or larger. When the beam is spread out I notice that the beam is not uniform, it contains round patches and there are radial patterns as well as show in this image:

Why does this happen? Is this an issue with the the lens or is it an issue with the quality of the laser?

This is very common. I have lasers that have this when unfocused, it can be the lens or the diode window or a defect in the diode itself. The round patches are likely the diode window or a defect, however you can easily tell if it's just the lens. When the laser is unfocused like in the photo, slowly adjust the focus and see if the round spots and patterns rotate as you focus the lens, if they rotate with the lens then it's the lens, if not then it's the diode or it's window.

You say a 5mW green, that means it's a 532nm DPSS, they have a more complex design with additional optics, so this can happen more easily.

Alan

 

[nikosb]

This is very common. I have lasers that have this when unfocused, it can be the lens or the diode window or a defect in the diode itself. The round patches are likely the diode window or a defect, however you can easily tell if it's just the lens. When the laser is unfocused like in the photo, slowly adjust the focus and see if the round spots and patterns rotate as you focus the lens, if they rotate with the lens then it's the lens, if not then it's the diode or it's window.

You say a 5mW green, that means it's a 532nm DPSS, they have a more complex design with additional optics, so this can happen more easily.

Alan

You are right, the circle patterns appear to rotate as the lens rotates so those are due to the quality of the lens. Any idea where I can find better quality lenses that don't have this pattern and give a more uniform beam projection? Also does it matter if the lens is made of acrylic or glass, does glass have better surface finish?

 

[Pi R Squared]

It won't matter but glass is usually better but at only 5mW acrylic is better or a more expensive single element glass lens because with a 3 element glass lens you will have some power loss. You said this was a cheap laser, it's probably not worth it, it may cost more than the laser did. Also it might not use a standard M9x0.5 threaded lens, if that were the case then don't bother.

Alan

 

[nikosb]

It won't matter but glass is usually better but at only 5mW acrylic is better or a more expensive single element glass lens because with a 3 element glass lens you will have some power loss. You said this was a cheap laser, it's probably not worth it, it may cost more than the laser did. Also it might not use a standard M9x0.5 threaded lens, if that were the case then don't bother.

Alan

Wehre do you recommend getting a "better" laser?

 

[The Lightning Stalker]

You can try cleaning the lens, but it's a
real pain. Anything that touches acrylic
can scratch it, so it has to be done with a
lens puffer and distilled water. If
puffing it doesn't work, then it almost
isn't worth it because the lens has to be
removed. That means breaking the glue and
if the cleaning is successful, it then has
to be refocused. Any little mistake and
the lens is toast and you have no laser.