I bought a green laser diode and i thought it would be a little dot like a pointer, instead it unfocused. HELP

Question

So the other day when i bought a green laser on ebay...i thought it would be focused and i could see the beam. Its 5mw and when i shine it anywhere it is a giant green blob with several dots within it...and the farther away i shine it, the bigger and more unvisible and unfocused the laser becomes. And theres no beam for starpointing like it said. WHAT IN THE WORLD IS GOING ON???? IS IT BROKEN OR WHAT?? IS A DIODE LASER NO THE RIGHT KIND OR SOMETHIN????? HEELLLLLP!!!!!!!!!!!!!!!!!

Answer 1

Well, a laser diode generally produces a wide beam. You need a special aspherical lens to shape that into a beam with minimal divergence. I bet you can also find that on eBay.

This is a typical case of "buyer beware". Don't buy if you don't know what you are buying.

At the very least you got a working laser diode. I would kind of doubt that it produces the advertised 5mW, but in your case 3mW and 5mW will be virtually indistinguishable, anyway. Except maybe that you can hurt your eyes with a 5mW laser much faster than with a 3mW laser, especially if you shine it in the pitch black where your pupils are wide open.

No person in a laser lab would ever work like that... without wearing the right filter glasses, that is. Which, again, is not particularly useful for "star pointing". Which again, is not useful, unless you have a telescope with adaptive optics. Which you don't have because you didn't know the first thing about your laser.

Hope this helps. Go get that aspherical lens and turn your laser into an eye-killer, tiger!

Answer 2

Laser diodes are very poor collimated devices. They are not capable of forming a dot. You have to play optical games with them to make them useful.

All laser diodes have a very short focal length lens in front of them. And it is adjustable. You can buy the lens assembly very inexpensively from many sources.

Don't be discouraged. This is part of the learning process. Instead, become an expert on laser optics!

Be sure and heat sink the laser diode so it doesn't overheat, and remember the case is usually positive, not ground!

Answer 3

A lens would work, but most commercial laser pens use a simple collimator (which is generally cheaper than a lens). You can buy collimators from places that sell lasers and laser pens.

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