About focusable red lasers: How much can I defocus?

Hi everyone,

This is my first post. I am planning to buy a 250mw 660nm focusable laser torch from o-like. While everyone loves to burn stuffs with these, and wants to have divergence as low as possible,I have a newbie question about defocusing them.

How high the divergence can be made by defocusing? Can I defocus it so that throwing it at a wall (say 10ft away) will produce a large (circular? maybe not) spot? If yes, the spot would be safe to look at even w/o goggles, because of less intensity.

Will my beam shape be sacrificed in doing so?

Yes. If focused near the aperture (for burning), the laser will create a huge (perfectly circular) spot on the wall, that is safe to look at without glasses. :yh:

This image should help illustrate a little:


From trying to figure out the rest of your questions:

-How high the divergence can be made by defocusing?..
Well, that really depends on your laser and the focusing lens assembly. The further you can screw it out, the larger the spot will get. Most lasers have a "stop" point that you can't go past, and other lasers, the lens just falls off if you unscrew it all the way. So your divergence can be over 200mRad if you de-focus the laser enough.

-Will my beam shape be sacrificed in doing so? ..
Well, your beam will change from a straight skinny line (collimated) to a cone-shaped beam. So, not really "sacrificed", just "changed" from a beam to a cone. You can always re-focus the laser to a collimated beam anytime you want. :angel:

Ash, thanks a lot for the helpful reply, it answered all of my concerns, time to get a 200+mw focusable red laser now!

edit: Just saw the link to your reviews of two red lasers in your signature, reading them now!

I hope you are gonna ' get some safety glasses. No doubt you are going to want to do some burning with you laser, and looking at the focused dot can leave permanent spots in your vision unless you use glasses.
Here are some for protection against red: link