Weird laser spot change

[murrat]

Did anyone noticed that when you shoot the laser to a wall (5m away) the dot of this 445nm LD is a small rectangle which has the long sides looking up and down and short sides looking sides
___________
I__________I

however if you check that rectangle at a closer distance (about 1m) it makes a quarter turn(90degrees) and long sides looking at sides.
__
I...I
I...I
I...I
I...I
I...I

weird?
:thinking:

I'll try to take a photo of these.

 

[Jufran88]

That's normal. I guess that is how the diode was constructed to be. Just focus to correct it. These diodes weren't mean to be used as laser pointers, but we did!

 

[Flaminpyro]

This is what you get with a multi mode diode

 

[LaZeRz]

yeh, i just wish they had a proper dot! much better for burning and pointing but they r pretty awesome already

 

[Cyparagon]

Yes. The fast axis is very small at the aperture, but since divergence is inversely proportional to diameter, this axis diverges very quickly. The way to correct this is to expand this fast axis.

Many people make the mistake of measuring the slow axis at aperture, and the fast axis at a distance when calculating divergence, which gives a false reading.

 

[murrat]

I solved why it seems weird.:beer:
It's just because of being so bright.
When you look at the photos carefully;
2 photos at near and 1 photo at far distance.
At far it can be easily seen that it is a rectangle but at near distance as it is not that big and so bright it looks like a standing rectangle.
However when you look at it carefully with laser googles you can see the small rectangle and brightness that makes it look different.