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Fun With Lasers


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Howto: Make a DVD Burner into a High-Powered Laser

red homemade laser

The laser pictured above has a peak output measured at 225 mW (average output 200 mW). It's a visible red at about 650nm. It can light matches, pop balloons, cut electrical tape, and so forth. It can do pretty much anything a Pulsar 150 from Wicked Lasers can do, because it's basically the same thing. The only differences? This laser was home-made, and cost about 1/3 the price.

So, how did I do it? Some luck, some deductive reasoning, and some electronics experience all come into play. This page is a brief guide.

Warning: This information is provided for entertainment purposes only. Lasers can be dangerous and proper safety precautions should be taken, including appropriate laser safety goggles. Working with electronics can also be dangerous. Lasers: dangerous. Electronics: dangerous. Danger: dangerous.




Step By Step

Step 1: Get a Laser Diode

DVD-RW drives are quite common today. The faster ones require a high-powered laser in order to generate enough power, fast enough, to do the job. I suppose it's the luck of the draw what exact diode they use, how it's powered, etc etc. This is where I got lucky.

This is the DVD drive I bought for $39.99 (Canadian), for the express purpose of tearing it apart for a laser diode:
BTC/EMPREX 16X DVD+-RW DL BURNER
BTC/EMPREX 16X DVD+-RW DL BURNER

Once I had the DVD drive, it took me less than 15 minutes to completely strip it and extract the optical works. There were two diodes, lots of little mirrors and things, and some circuitry. It took another few minutes to extract the two diodes with their heat sinks. The rest of the optical bits and pieces were saved, as was the motor that opened and closed the drawer - it can be used, with a mirror, to do effects. Everything else was junked.


Step 2: Test the Laser Diode

Once you have the diode out, you need to figure out how to make it go, if it's visible or not, and if it's got enough power to make it worth your while.

The laser diodes I'm familiar with look like this:
5.6mm laser diodes

They may not look exactly like that, though. Here's the actual diode and heat sink I took from the DVD drive:
DVD diode

Since everything connected to the computer chassis was at ground, and the diode was soldered to its heat sink and the sink was bolted to the optical assembly which was attached to the DVD mechanism which eventually was tied to the computer chassis, I reckoned that the DVD diode's case was ground. That meant one of the other two pins was the +vdc.
Knowing that most laser pointers ran on 3v (two AAA batteries) I got a 3vdc supply and - aiming the diode emitter window away from me - I hooked (-) to the heat sink and touched (+) to one of the leads.

Presto! A huge flood of monochromatic red light all over my desk. So, I had a visible red laser diode!

How powerful was it? The best I could do was hold it a mm or two from some thin black plastic and fire it up. It melted through the plastic in a few seconds. Yep, it was strong!
Movie of DVD diode going through plastic. (download and view offline)

In order to use the diode though, I had to get the laser diode out of its wierdly shaped heatsink. It was soldered in, and I know heat can be lethal to laser diodes, so it was a trick getting it out. I used solderwick to extract the solder, set my iron on fairly hot (short uses at high temp is better than long uses at medium temp), and managed to get it out without hurting it. Needle files were then used to clean off the rest of the solder, rather than risk more heat with the iron.

If you're lucky, you might even get a laser diode that is conveniently identified like this:
easy to use diode
GND is ground of course, LD is the Laser Diode, hook Positive here, and the third pin might be a photodiode or might be unused.


Step 3: Lenses and Mounting

This turned out to take me a long time. I bought a cheap red pointer with plans to tear it apart and use its lens etc but it was junk. After lots of internet searching and reading, I found what I wanted. A metal 'heat sink' tube that held the 5.6.mm diode, and was threaded to accept a collimating lens. The only problem was it was a bit expensive - about $20, plus shipping.

Then, I received a laser module I'd ordered from AixiZ Lasers. It looked like what I was looking for... I took it apart and confirmed it! Not only was it the heat sink mount, but included the lens and an extra tube at the back to house a driver and facilitate mounting in an enclosure!
laser module

I immediately ordered another module from them: 10mW, 650nm. This module was only $12, plus $5 shipping. So for $17.00 (US) I had a complete mount and matching collimating lens!

The 10mW 650nm laser diode unfortunately did not survive the procedure of extracting it from the heatsink. The diode was press-fitted into the heatsink using friction to hold it still. Extraction involved use of a hammer directed towards the front-end of the diode to force it out the back of the heatsink. Nuff said.


Step 4: Power and Control

With the laser diode, mounting hardware, and collimating lens, all that remained was to do the electronics. I already knew, from looking at the guts of a Pulsar, that you could run a red diode without any driver at all - just wire it straight to the batteries. That made it a lot easier.
I still had some requirements though. I wanted the option of constant-on so I wouldn't have to mess around with rubber bands, twist ties, or clips. But I still wanted momentary use too. And I wanted an indicator LED. Also, I wanted to use rechargable batteries, so I wouldn't have to keep filling the landfills with dead alkalines. Finally, I wanted to use AAs, for longer life between recharges.

So I opted for two AA NiMH batteries, a three position slide switch, a pushbutton, and a LED:
A simple schematic

Pretty simple, the slide switch is 'off', 'momentary', and 'on'. When it's 'on' the laser is on full time, and the pushbutton does nothing. When the slide switch is 'momentary' the laser is off, until the pushbutton is depressed. The LED is wired with a 1k-ohm resistor, in parallel with the laser diode. The LED comes on whenever there is power going to the diode.


Step 4a: More Power!

For diodes rated at 3 volts, running them off two NiMH batteries is really under-powering them. It's not bad for the diode, in fact it probably will contribute to a longer life, running them under spec, keeping the temperature down. On the downside, it means that you won't get the full potential out of the diode.

After running my DVD laser for a few days or so at 2.4v and with an average output in the 115mW range, I decided I wanted more power. My design still constrained me to using rechargable batteries that were fixed in place, so I couldn't just switch to alkalines and call it a day. Instead, I added a third NiMH cell - for a total of 3.6v instead of 2.4.

Now, 3.6v is the nominal rating, when fully charged it could be pushing 4 volts, and I didn't want to fry my laser, just pump it up a bit. Still not worrying about a proper driver, doing things on the cheap and simple, the easy answer was... Add a silicone diode in series! Silicone diodes like a 1N4001 have a forward voltage drop of 0.6 volts. 3.6v - 0.6v = 3.0v! So nominally that will give me a full 3 volts to the diode. And when the NiMHs are fully charged, I might see 3.4v to the diode but that's about what it'd get with brand-new alkalines.

Certainly, a proper driver board with current limiting and voltage control would be ideal, and there are definately lots of options out there if you want something like that. Check Sam's Laser FAQ for diode controllers if you want to go that route. For me, I guess I'm just a risk-taker ;-)

Here's an updated schematic, showing the three cell battery, the 1N4001, and the DC power jack used to charge the laser:
schematic


Step 5: Putting it All Together

The last step is to pick a case and put it all together. Or maybe that's the 4th step? The case will dictate what size / kind of batteries you can use, or the batteries will dictate what size of case you require.

The cases I went with are plastic, just over 4 inches long, about 1.5 inches wide, and 1 inch high. My design was to use AA sized batteries but my case is too small for conventional battery holders. So I went with solder-tabbed batteries, and permanently mounted them in the case. So they can't come out to charge. So I added a DC power jack, to allow me to charge the batteries in place.

I used a little bit of bread-board to solder my switches, LED and resistor to, and then just soldered everything up into the case.

Here's an annotated picture of the laser's insides. Click the thumbnail for the full-size view (of the 2-cell version):
Annotated laser insides

I like the layout so much that I have built four lasers into this format now: the DVD diode one, plus two from modules bought from AixiZ Lasers, and one from a green laser pointer I got from ebay and then destructively dissassebled. I will continue to use this format for any other handheld lasers I build, that can be fitted into this size.

Here's a closeup that shows the little circuit board:
635nm 10mW laser
This photo is actually of the 10mW, 635nm laser I built with an AixiZ module. As you can see it's almost identical to the 200mW DVD laser. How do I tell them apart? #1 I have put labels on the bottoms identifying them. #2 I have put labels on the back end by the DC jack identifying the charge voltage (the DVD laser uses higher charging voltage). #3 The indicator LEDs are a different style for each laser. #4 the Danger label identifies the wavelength and power.

Here's a group photo. - four homemade portable lasers, plus a fifth empty enclosure waiting to go:
four homemade lasers
The IR laser is in the white enclosure to ensure there is no chance of mistake. The invisible beam is too dangerous to risk anyone thinking it's just a 'dead red' and looking into it.


Alternate Case Style
Here's something I just stumbled across as a potential alternative case: Over at Lasermate, they have a Do-It-Yourself Pointer kit. I haven't bought it so I don't know for sure, but it might be possible to adapt the kit, to fit the high-powered diode into it somehow. The driver board in the kit would probably not work or would need adapting, in order to supply enough current. Actually I might try this later, just for the heck of it.
DIY laser kit




Summary

All-in-all I'm very happy with the results. I have and probably will continue tinkering with it, there's still a wee bit of space left inside the enclosure so I might still be able to pack a bit more functionality in there somehow. From a pure output standpoint, plain and simple, it rocks. It was also a great learning experience and something I can be proud of: I made it myself.

There are some concerns of course about the longevity of the diode; I know I'm pushing it a little hard and I know that sooner or later it's going to cook off and die. Running on the three cells (3.6v) it gets hot after about 60 seconds so I have to impose a duty-cycle on it. Running at 2.4v I ran it for several minutes and it stayed cold. Still, it's a risk I'll take, considering what little it cost me.

And now, here are the specifications as of 12 September 2006:

Laser Diode Characteristics
  •  Wavelength: 650 nm (estimated)
  •  Output Power: 225 mW peak, 200mW average (measured with Coherent LaserCheck)
  •  Operating Voltage: 3.0 volts DC nominal
  •  Operating Current: 350 mA (approx)
  •  Duty Cycle: 60 seconds on, 60 seconds off

Power Supply Characteristics
  •  Battery: Three "AA" size NiMH Rechargables, permanently installed
  •  Operating Voltage: 3.6 volts DC, nominal. 4.0 volts DC, maximum
  •  Battery Capacity: 2000 mAh
  •  Charging Voltage: 4.5 volts DC maximum
  •  Charging Current: 200 mA for 12 to 14 hours

Here's a picture of the inside of the laser:
Inside DVD Laser
Three AA cells give me 3.6 volts at 2000 mAh. At about 350mA operating current, that gives me just under 6 hours of use between recharges. Trickle charging takes 12 to 14 hours at 4.5 volts and 200 mA. Rapid charging is possible but not recommended as I have not included a thermister or fuse in the battery pack so there is no way for the rapid charger to accurately measure battery heat.

The information presented above represents my own results obtained with one single diode taken from one DVD player. I am not an expert just a dedicated hobbyist. These results are not guaranteed and you may find your own experiences to be different. In other words, As always, Your Mileage May Vary.

Note that at these power levels, protective eyeware should not be considered optional - it's a must!
Protect your eyes! These are serious power levels. At 200mW, I can feel this laser stinging my arm (and I'm somewhat fair-skinned) in about two seconds. And that's an unfocused, 1/8" diameter beam!
Play Safe!


Images and text copyright © 2006 Stephanie Maksylewich