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Would A Fixed Focus Laser Burn?

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Kmssd

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After I built my first laser I thought about the old lasers you got for running the pets around. Could a laser have a fixed focus like one of those and still be able to burn if the output was high enough (able to burn through an adjustable focus lens)?
 





I have a 400 mw blu-ray and it burns like mad if you have it focused to infinity.
 
joeyss said:
I have a 400 mw blu-ray and it burns like mad if you have it focused to infinity.
Click to expand...

All I have is a red, roughly 250mw. When you say "focused to infinity" do you mean focus the dot/beam on something really far then whatever is close will burn?
 
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Red can have a hard time burning, but the dot will make heat on some things. Try coloring your hand black and see what I mean. It will sting so bad you will want to take it off. Pretty much the only thing a 250mw red can do while focused to infinity is melt dark plastics. You may be able to light a black match. Blu-ray is much better for burning.

Edit and yes that is what I meant.
 
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joeyss said:
Red can have a hard time burning, but the dot will make heat on some things. Try coloring your hand black and see what I mean. It will sting so bad you will want to take it off. Pretty much the only thing a 250mw red can do while focused to infinity is melt dark plastics. You may be able to light a black match. Blu-ray is much better for burning.

Edit and yes that is what I meant.
Click to expand...

Yea, I know about coloring stuff black. I wasn't too worried about burning with a red, I just picked red for my first build. I was thinking about a fixed focus for my next build idea so it could be a nice even beam as far as the laser could throw it.
 
For burning you need high power density. Focusing helps a lot, but strong lasers burn even without focus, or focused to infinity. Focused to infinity still means the beam will diverge, and for burning purposes it will diverge rather fast, so expect any non-focusable lasers to burn only near the lens of the laser.
Anyway, if the question is 'should I pay more for focusable laser', then answers is yeah, sure, it's the cheapest option to improve burning. It's also kind of safety feature, you can keep your laser focused into wide cone if you are not burning, which makes it much less dangerous.
 
Kmssd said:
After I built my first laser I thought about the old lasers you got for running the pets around. Could a laser have a fixed focus like one of those and still be able to burn if the output was high enough (able to burn through an adjustable focus lens)?
Click to expand...


You can use a glass magnifying lens to focus the "fixed focus"
Laser's beam to the smallest point for burning..
That will give you the highest power density of your Laser.

It is the same as using a magnifying lens with the Sun and
burning things... The sun's power is "fixed"...


Jerry
 
Except watch for reflections when using magnifying glass.
 
DrSid said:
Except watch for reflections when using magnifying glass.
Click to expand...

Agreed....

But if you are using a >5mW Laser you SHOULD be wearing
Laser Safety Goggles/Glasses..
And the Safety Safety Goggles/Glasses aid in focusing the
beam to the smallest size....


Jerry
 
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Glasses are a definite, this is thinking out loud for my next laser which will be a blue.
 
Well with 445nm even collimated beam burns up to several meters. And all models/builds I've seen were focusable.
 
DrSid said:
Well with 445nm even collimated beam burns up to several meters. And all models/builds I've seen were focusable.
Click to expand...

Agreed; my 1.7W 445 can light a red-tipped match from 30 feet away when focused to infinity.

My 275mw 635 can light a black-tipped match from around 10 feet.
 
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