Ebay Lasers?

[Kelth]

Hello all! New to the fourms, heres the thing, for one of my final projects in a freshman engineering course we need to build a little robot and have it do something, (BOEBOT from Parallax), and well i was kinda tired with everyone's ideas doing stuff really simple, so i thought that id build a sort of tank, with treads, and a color sensor on a turret, the tank would roam around looking for its target, a blue dot would signify the target and then once if found the target it would "fire", so i thought it would Dazzle the class ( :-p ) if i put on a laser capable of lighting a match on fire, or a baloon or something.

i stumbled upon this tutorial ( http://www.felesmagus.com/pages/lasers-howto.html ), i so happened to have had a dead dvd burner laying around (oooh sony) so i tore it apart and extracted the laser, tested it, hoho! it worked but then something horrible happened, i got clumsly and the hit the + and - together and fired the diode.

so now im thinking how i can get another diode. and so i looked on ebay, no dead dvd burners. but there are a few diodes, for sale, some claim to be 100mW and even a 500mW diode, 500 seems kinda suspicious. Would any of you trust buying a diode from ebay or is it just a waste of money?

[BoomDog]

Well, as you know, there is always a risk when ordering on Ebay. My experience, however, is that most of the laser "fraud" occurs with laser "pointer" modules being resold from Wicked Laser, Dragon Laser, Laserglow, or even Leadlights. The diodes themselves are usually for real. 500mw red is not unheard of, so unless they are asking for a really low price with no reserve, I wouldn't be TOO concerned about it. Just ask the person in charge of the auction some related question that only someone who knows a bit of lasers would know (something about beam diameter, convergence, etc.). If they can answer that, there's a pretty good deal it's the real thing.

BTW, cool idea with the robotics project!

[buffo]

There are some serious safety issues involved in placing a laser diode powerful enough to pop a ballon on an autonomous device... If the thing does something unexpected, you need to be sure that the beam from the laser won't be reflected into the eyes of your classmates as they watch the robot motor around the room.

At a minimum, you'll need goggles for everyone in the room. That is going to be expensive. (Unless you've only got 5 people in the class...)

Also, 100 mw of red from a DVD burner is just BARELY enough to pop a ballon under ideal circumstances. Make sure you use a black ballon. The diode will need to be quite close to the ballon, and you'll probably need to play with the focus a bit.

An IR diode would probably work better simply because you can get a lot more power for the same money if you go with IR. However, you won't be able to see the beam, which sort of defeats the purpose of your demonstration.

What is your budget, and how long do you have to complete the project? Finally, what do you intend to do with the laser when you are finished with the class? The answers to these questions will make it easier to offer suggestions.

Adam

[Kelth]

the autonomous device is reletivly small, maybe 6 inches long, 3 inches wide, and 2.5 high. I have no concern for any reflection of light becuase there is nothing that will reflect it so close to the ground, floor is carpet, there is a 5 inch tall black rubber liner agaist the wall, and all of the chairs/desk legs are also non reflective.

As far as distance, I can always set up distance finding so i can move closer to the "target" close enough so the desired effects will take place. Iv only got a meager budget of about 50-70$.

As far as with the beams, if i can still light a match from a distance, then thats probally an effect enough. i can always put a sort of dummy laser, or cheap laser point to make an "effect" while useing a non visible beam to do the really fancy part.

id like to get into lasers afterwards, not so much lightshows but i have a few interesting ideas. However, anything dealing with lasers seems to be an expensive hobby to get into.

[BoomDog]

However, anything dealing with lasers seems to be an expensive hobby to get into.

It is! I'm just now dropping $3000 on laser and scanner parts, and to some people here, even THAT is pocket change compared to what they've spent on their lasers. :P Don't let that bother ya though; you can still get some really cool lasers (particularly to new hobbyists) for $200-$500; ya just got to save your money.

$50-$70? That's a pretty small budget; you'll have a hard time getting a laser that can do that for that price. IR is always the cheapest and best for burning, but as mentioned you can't see it and because of that, can be relatively dangerous. Not to mention, it's a big pain to focus (even with a focusing lens) just because you need to look at it through "nightvision mode" of a video camera, or other methods that are way out of this price range.

You may be able to gut a DVD burner or something, but those usually have 40-80mw reds, which only about half the diodes in that range will be able to pop anything. There are alot of guides out there on how to do this, but it's no walk in the park.

Best of luck!

[Kelth]

thanks alot for all the great information, agreed my budget for this project is small but im hopefull i can get something work. Later when i get more, a gas laser sounds like alot of fun... but that comes later on :-p for now im just trying to get a diode that would work for some fancy trickery! could i make use of some sort of frequency doubling lense perhaps to get more out of a dvd burner diode? Ill post on how sucessfull the project became :-p

[BoomDog]

Crystals like those (for instance, those found in DPSS lasers) only work for a thin specific range of wavelengths. That's why you can't just gut a 1064nm-to-532nm crystal and send an 808nm diode through it for violet; you have to purchase a different and much more expensive crystal for that. Not to mention, it really wouldn't do anything beneficial for you anyway, except make an IR laser visible. When that occurs, you are changing the way that energy would be absorbed by the material you are trying to burn. Most materials absorb IR, which is why it works so well, but only certain ones (red and black colored items) absorb green (for example). Not to mention, not all of the IR will get doubled in the crystal, so you will have a lower-powered colored laser with some IR leakage. Plus, crystals are pretty low efficiency, so you lose a ton of power inside them anyway.

Keep us posted! :P

[Astroguy]

thanks alot for all the great information, agreed my budget for this project is small but im hopefull i can get something work. Later when i get more, a gas laser sounds like alot of fun... but that comes later on :-p for now im just trying to get a diode that would work for some fancy trickery! could i make use of some sort of frequency doubling lense perhaps to get more out of a dvd burner diode? Ill post on how sucessfull the project became :-p

PLEASE remember red or IR if it is enough to pop a balloon it is enough to fry your eyes.

[liteglow]

PLEASE remember red or IR if it is enough to pop a balloon it is enough to fry your eyes.

Yea I know... I got some hot spots on my eyes from my RED laser !!
I did get hit by a 50mW green laser, but that dot did go away after some weeks..
But I did get hit by my 400mW red laser directly into the eye, and I now have a tiny spot that I always se when I blink my eyes :|
It`s a nice reminder of using safety googles...