Laser quality

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Longtom
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Laser quality

I have a cheap ass laser I use to play with my cat and point at things. I noticed that the dot gets pretty fuzzy and large at about 10ft or so. That got me to thinking: If I’m looking at a laser online, how can I know the quality of the beam? Sure, I can read numbers like how many watts it consumes or what color it is on the electromagnetic spectrum, but how do I know how tight and accurate the beam is?

Now, a light beam will cross itself at a certain distance and then spread back out, right? I’m sure that lasers are rated for a certain distance where the beam is the tightest, right? How do I know?

Enderman
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The fuzzyness is called speckle, all lasers have it, there are things called speckle reducers: https://www.edmundoptics.com/optics/laser-optics/laser-windows/Optotune-...
The tightness is measured in milliradians, which is the divergence.
It will only “cross itself” aka focus at a point if it is overfocused.
If it has an adjustable beam then this is possible, if it doesn’t have an adjustable beam it will either have a set focal point or it will not have a focal point, so it just goes straight and diverges from the aperture.

Longtom
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thanks!

So, I just read that most lasers have a 1 milliradian divergence. Does that mean that I can’t really use that to judge the quality of the product I’m viewing?

Furthermore, if I’m buying a laser that’s of unknown quality, as long as it has a focusable beam, I should be okay?

Bear with me. I’m learning, here.

The_Driver
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How do you define the quality of a laser? There are like a hundred aspects one could take into consideration.

If you don’t want to spend a fortune you will have to live with the speckle.

Many Chinese pointers have a focussing lens. This makes the much more dangerous though.

Longtom
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Thanks.. I guess…

Angler
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Longtom wrote:
I have a cheap ass laser I use to play with my cat and point at things. I noticed that the dot gets pretty fuzzy and large at about 10ft or so.

What’s an ass laser? LOL

With the ultra cheap lasers you find at walmart and such I have noticed this,
but not really an issue once you get above the $10 price range or so.

These are great if you want something cheap. I have the 405nm violet one and it is still a small dot pointing it 1/4 mile down my street. My cat loves it.

DoubleA
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Angler wrote:
What’s an ass laser? LOL

You would’ve understood if you were Japanese. LOL

and on the first day he said "Let there be light"...

wle
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usually the $7 and up lasers, that use 18650 cells, have some kind of focus mechanism, though you may have to take the thing apart and screw the laser in or out to do it

some have it on the outside

wle

Longtom
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Thank you for the suggestions, guys.

I’ll take a look at those, Angler and wle. I appreciate it a lot.