How to Light a Match with a Laser
From UIC
How to light a match with a laser diode
Contents |
| Infos | |
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| Author: | quequero |
| Email: | 
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| Website: | http://quequero.org |
| Date: | 04/10/2007 (dd/mm/yyyy) |
| Level: | Difficulty:  Price: less than 15 euro |
| Language: | English 
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| Comments: | |
Introduction
Update: 10/Dec/2007 - corrected a wrong connection on laser driver circuit schematic, thanx to Zmaster.
If your dream was to cut people in two halves with a laser, or you love Darth Vader's lightsaber more than your girlfriend, or you just love shiny things.... This is the right place for you: what I'm gonna show today is a simple hack to turn a tiny laser diode into a cool blow-torch :). Well ok, it's not gonna be a real blow torch, but trust me you'll have a lot of fun, so let's begin!
What we need
We need just a few components that are very easy to get from various sources:
- One laser diode (I'm using a SLD1236V)
- One 6 ohm resistor
- Two capacitors (10uF polarized and 100pF)
- One diode
- One LM317-T
- Some optics to collimate the laser beam
Where do I get the laser diode?
Now you could be asking: ok it's quite easy to get all these components, but I really don't know where to buy a laser diode. That's right, laser diodes on ebay are not that cheap, and most of them are IR (infrared) lasers, so they're not going to be so useful if you like shiny things :). What can you do? It's simple: just buy a broken DVD burner, most of them have a full working laser diode ready to be extracted, and their price goes from 0 to less than 5 euros... Really cheap :).
I have a broken cd-burner, is it ok to use its laser diode?
I'm so sorry, but you can't use a diode that comes from a cd burner, mostly because you'll find yourself handling an IR laser, that's either dangerous (you can't see IR radiations but your eyes can be seriously injured!!!!) and not funny because it's completely invisible.
Which brand is better if I want to buy a dvd-burner?
The brand doesn't matter, just be sure that the writing speed of your dvd-burner is not lower than 12x. More speed means more laser power, because at higher speeds the laser itself has less time to dig a pitch on the surface of your dvd. The other reason we are using a dvd burner laser is that they use a nice red (and visible) laser.
What about the optics?
Laser diodes don't emit a collimated beam, instead they emit an ellipsed-shape beam that's not so useful to burn things (but of course is really useful if you like olographic photography). So you'll need dedicated optics, but don't worry: you can find some really cheap optics here, just buy the laser module you like. Keep in mind one thing: it's very likely that you'll have to destroy the embedded laser to reuse the optics on your new laser diode. Anyway I bought this one: 650nm 5mW laser module 3VDC adj. lens 650 nm for 4$.
Installing the optics
Take your optics module and remove the embedded laser diode. Mine was very well enclosed and I had to use a screwdriver... So long diode and thanx for all the fish. Now install your new laser into the module using a vise, but be careful it's very small and fragile. This was the easiest part, let's build the circuit now.
The circuit
Now you have all your components right? Cool, but we need to build a very very simple circuit to drive the laser. Here you are some precautions you'll have to take into account if you don't want to fry your beloved diode:
- Laser diodes are static sensitive components, they are really sensitive to electrostatic discarges, so be careful and wire your wrist with an antistatic wrist strap (a simple cable in series with a 1 megaohm resistor connected to the ground) while handling your diode!!!
- They really hate heat, so if you overload them and you're not careful they're gonna fry readily.
- Laser diodes are current-driven circuits, this is important, and that's why you can't wire them directly to a battery :).
Ups, I forgot to mention something: we are going to overdrive our laser A LOT, this is a bad practice because laser's life is gonna be shortened a lot and bla bla... :p. Ok let's talk about the circuit: as you can see it's really simple, we are just using an LM317 as a current source (point 3), so we'll be able to drive our laser just by turning our 100ohm potentiometer.
A laser diode has at least three pins, one is common and is welded to the metal box, one is the anode... And the third? It's the anode of the embedded photodiode that should be used to keep the emitted power under control, to avoid to kill the diode, guess what? We are not going to use it...
The diode I'm using has a threshold current of 50mA (@20°C, lasing current varies quite a lot depending on room temperature), an operating current of 130mA and an operating voltage of 2.5V. As you can see I put a 6 ohm resistor in series with the trimmer, why? This is just a simple protection, when the trimmer is set to 0 ohm the LM317 supplies as much current as he can until the diode burns. The first and second capacitors are used to avoid unwanted spikes that are really dangerous for the laser diode.
Scotty beam me up!
It's time to power up the diode, move your trimmer/potentiometer to the highest resistance and connect your battery/power supplier. Now slooooowly turn the trimmer, you'll see a dim light coming out from the diode (hopefully ;p), when the current will reach the threshold value the laser will quickly start lasing, and you'll surely notice the difference! Be careful, don't look at the beam directly (or reflected) or you'll be blinded in less than a millisecond, always wear protective goggles or use a pair of dark sunglasses, they could help. Now it's time to do a little bit of collimation, choose the distance where you need your laser to focus, put a dark sheet of paper in front of the beam and turn the optics until you see a very very small spot of light. That's all, put your match at the focus and wait some seconds... You should see something like this:
Some Warnings
- Be careful, this kind of lasers is VERY dangerous, the beam is dangerous even if you look at it on a surface painted in white (like a wall), so always wear some kind of protection for your eyes!!!
- My laser diode has been designed to work with 130mA in continuous mode, you can safely overdrive it with a lot more current (I reached 450mA for 10 seconds) but you'll need an heatsink or a peltier cell to keep it cool, otherwise it's gonna fry very very quickly.
- If you have an old heatsink and a drill, just make a hole and push the laser inside with a little bit of thermal compound, you'll be able to keep the laser on at its full power for much more time.
- You should never keep your laser on for more than 30 seconds if you're overdriving it and if you don't have a heatsink, after turning it off wait at least a minute to let it cool down.
Greetings
Greetings goes to senkat for sending me the diodes and to daedal and wildfisting for their advices.
Disclaimer
If you become blind it's not my fault, I told you to use protective goggles, and stay AWAY from reflective surfaces!!!
