It used to be that lasers were big bulky expensive things that
required a laboratory to run and an entire factory to build. I remember the
first He-Ne laser I saw two decades ago, the size of a small telescope and
probably not more powerful than the laser pointer I carry on the keychain
nowadays. Well, not anymore. It's pretty easy to build a laser today, on the
kitchen table or in the garage, for a surprisingly small investment. The goal
is to make a laser capable of burning small objects, such as a piece of paper,
a balloon, etc, while keeping the whole project cheap - even as cheap as $35 if
you don't make any mistakes. Here's how.
What to expect
Here's a video I made of the two lasers I built recently. They can
make holes in a piece of paper, can pop a balloon, ignite matchsticks, melt
duct tape, etc.
That is what you should expect to be able to build after reading
this guide. Looks fun? Okay, keep reading.
The extremely easy but pretty expensive way
This is cheating - you're not building a laser, you're just buying
one made by someone else. It's also probably one of the most expensive ways,
but the effort is minimal.
A few details to keep in mind:
Things get really interesting if the laser power is 100 mW or
more. Less than that, and it's pretty hard to burn or ignite objects.
At the same power, green lasers appear much brighter to the human
eye than red or blue. So, if you want a laser that looks very powerful in
addition to being very powerful, get a green one. But be prepared to pay a
significantly higher price - green is expensive.
Prices will vary widely, but be ready to pay $200 for a red 100 mW
laser, $300 for a blue one, probably more than that for a green laser. More
powerful lasers cost more, less powerful cost less. A 500 mW green laser can be
as expensive as $3000.
The easy and cheap way
Go on eBay and search for "laser module", "laser
kit" or "laser diode". There are plenty of sellers who will
provide you a full laser kit that you can assemble at home. This is the diagram
of a basic diode-based laser:
Typically, they will sell you the driver circuit, along with the
diode encased in a small tube that contains the lens. Sometimes you can buy
just the tube with the diode and the lens, and the driver circuit can be
purchased separately.
In any case, make sure the lens can be adjusted. You may want to
tweak the beam, focus it at different lengths, or make it parallel, which is
not doable if the lens is fixed. Also, glass lenses are better, but more
expensive than plastic; either one should work just fine for a small home-built
laser like this.
The driver circuit needs to provide a fixed current (not fixed
voltage, but fixed current) to the diode. The range for most diodes is between
30 mA and 250 mA. The bigger the current, the more powerful the beam, but the
diode's life will be shorter. Most diodes, when fed 100 ... 150 mA, will
produce a 100 ... 150 mW beam, which is plenty fun - also, that current level
is acceptable for most diodes and won't make them die prematurely.
Most drivers are adjustable, and that's the kind you want, in
order to tweak the current that goes to the diode. A digital multimeter, if you
have one, would be very helpful here, as it will tell you exactly what's the
current through the diode.
Of course, you can design and build the driver circuit yourself
from scratch, if you have the knowledge. Something based on the LM317 circuit
should be okay. Make it adjustable, and be sure to measure the current you're
sending to the diode. Protect the output against spikes with an R-C circuit (10
microF and 1 k-ohm, or something like that) in parallel with the laser diode.
Currently (May 2010) you can buy a 80 ... 150 mW blue laser (405
nm) kit, including the diode+lens assembly tube and the driver circuit kit
(parts and circuit board, including schematics, that you need to solder) for
approximately $30 ... 35 on eBay from some sellers in Asia. You can probably
find red laser (650 nm) kits even cheaper. Or you can buy just the tube with
the diode and lens, and you can find the driver circuit on eBay or somewhere
else already assembled, if soldering is not your thing, and it won't be much
more expensive.
So, you don't have to be an electronics wizard to do this. If you
buy a pre-assembled driver (something like $15 ... $20 online) you therefore
skip the soldering part, and all you need to do is hook it up to the diode.
Everybody can do that, right? :)
WARNING: Always first connect the laser diode to the driver, then
connect the driver to the battery! Never connect the driver first to the
battery - this will kill the diode! Laser diodes are not LEDs, they are very
sensitive. Connect the diode to the driver and leave it connected forever, this
is the only way to avoid mistakes. I burned a lot of diodes before I figured
this out.
The somewhat harder but very cheap way
Some of the things I said above still apply - you still have to
buy or build a driver circuit. But, instead of buying the laser diode, you can
extract it from an old DVD or Blu-Ray writer.
"What? Does that mean I already have the diode somewhere in
my house and I'm not even aware of it?"
That's right. DVD writers that can write disks at 16x speed or
faster (that's writing speed, not reading speed) contain diodes usually at
least 150 mW if not more powerful. A DVD writer will provide a red (650 nm)
diode, a Blu-Ray writer will provide a blue-violet (405 nm) diode. All that's
required is that the writer can still write disks. It doesn't matter if it
makes a lot of coasters so it's time to retire it, all that counts is the raw
burning power.
Most (but not all) diodes look like this:
Some will lack the transparent window at the top (open-case
diodes); some will lack the case altogether - those are more fragile and you
can easily break them. The best ones are fully encased in metal, with a transparent
window at the top, as shown above. They are very tiny anyway, smaller than a
penny - be careful how you handle them.
So, just break the DVD writer open and rummage inside for the
diode. I won't provide too many details, there are plenty of instructions
online if you can't figure out yourself which one is the laser diode. Google it
if you're lost. Also keep in mind: there are usually at least two diodes
inside, and only one of them is the powerful laser diode used for writing. The
other one might be a much weaker infrared diode used for reading - that's not
the one you want.
Again, it has to be a DVD writer (not a DVD reader, not a CD
writer, not a CD reader) at least 16x writing speed, or a Blu-Ray writer (not a
Blu-Ray reader).
This is how to connect a red (DVD) diode to the driver:
This is how to connect a blue (Blu-Ray) diode to the driver:
Once you have the diode, connect it to the driver (pre-configured
at 85 mA or something like that) and after that (not before!) connect the
driver to the battery. The diode should be INCREDIBLY BRIGHT. If it's not very
bright, if it's just like an ordinary LED, you broke it - you can toss it in
the garbage can at this point.
To focus the beam, you can use an ordinary magnifying glass, and
that should suffice for a few experiments. But there's a better way: purchase a
laser lens tube assembly online, containing a much weaker diode, and swap the
diodes.
There's a small company called AixiZ (I'm not affiliated with them
in any way) who sells very small (5 mW) laser diodes (these are just like a
laser pointer, very safe, but they can't burn anything) in a tube with
adjustable lens, for a very small price - they are around $5 online or on eBay.
Buy one of these, very gently extract the small laser pointer
diode, and instead install the more powerful burner diode. After that, just see
above - connect it to the driver, set the current, enjoy.
Make sure to adjust the lens: focus the beam as small as possible
at the distance you want to burn objects. The smaller the dot, the easier it is
to burn. I managed to pop balloons, poke holes into paper, etc. with a 95 mW
laser, but the beam was focused to the size of a pinpoint. Also keep in mind,
if you focus it that small at, let's say, 50 cm from the lens, then it's only
truly effective at 50 cm, no more, no less.
The very hard way
One could argue that even the previous method is
"cheating", since you're not really building the laser diode
yourself, you're just buying it or extracting it from another device. If you
agree with that, a diode laser is off-limits - you can't make a laser diode
from scratch in your garage. A gas laser is the only way.
This is a huge project. Essentially, you have to make a big glass
tube like the ones used in neon signs, put it between two very special and very
carefully calibrated mirrors, feed the whole thing with very high voltage (20
kV is common), and pray it works.
The gas inside the tube can be:
- a mixture of helium and neon (the He-Ne laser); this one
generates an orange beam, is one of the easier gas lasers, was widely used
before diodes took over
- mercury vapors (the Hg laser); makes a bright green beam, it's
somewhat harder to trigger but the materials are easier to come by (a drop of
mercury)
- nitrogen gas (the N2 laser); this is an invisible laser,
ultraviolet, one of the easiest to trigger, but... well... it's invisible, so
it's less fun
- carbon dioxide (the CO2 laser); also invisible (infrared), also
easy to trigger, used by the military to make laser weapons
This is not for the faint of heart. It requires careful
preparation, a pretty long execution time and, last but not least, the
investment may not be trivial - you need a vacuum pump, you need to purchase
the special mirrors, you need to make or order the special tube, you need a
high-voltage power supply, etc. You can probably stay below $1000 if you know
what you're doing, you're lucky, and you're good at dumpster diving, but expect
to invest a few months of work anyway. If you're extremely lucky and extremely
persistent, you can probably beg or dig up all the parts you need for next to
nothing - so it's a balance between price and effort/patience.
I have not done anything like this. Back in high-school, I
attempted to build a Hg laser, and failed when I couldn't procure the "magic
mirrors". I would very much like to make this old dream come true. But
it's a lot of work, so... we'll see. The little diode lasers I made so far are
so much fun, so for now I'm satisfied.
Laser safety
A LASER THAT CAN BURN THINGS IS DANGEROUS!!!
Remember, you're not building a toy. This is a device that can do
permanent damage to your eyesight and all it takes is a fraction of a second -
faster than you can blink. Also, obviously, you can start a fire by mistake -
the risk is small but not zero. The Wikipedia page on laser safety is very
good, make sure you read it before you start working on this project:
This is the bottom line:
Lasers below 5 mW are "class IIIa" lasers (or class II,
or I). These are the laser pointers you can buy for $5 at the corner shop. They
are not dangerous, you can play with them any way you like.
Lasers between 5 mW and 500 mW (the kind this document teaches you
to build) are "class IIIb" lasers. Damage to the eye can occur pretty
fast. It is recommended to wear laser goggles while working with such lasers.
The goggles are fine-tuned to the specific wavelength of the
laser. So, if you build a 650 nm red laser, you need to buy 650 nm goggles; for
a 405 nm laser, buy 405 nm goggles, etc. The color of the right type of goggles
will always be the complementary color of the laser, so for a blue laser the
correct goggles will be orange-red, etc.
In any case, you can't replace the laser safety goggles with
sunglasses or a welding mask or anything else. These goggles are fine-tuned
devices, specifically made for one purpose only. Nothing else is effective, not
even close.
The same sites that sell ready-to-use lasers usually will also
sell goggles. See the links above. Or google "laser safety goggles"
and choose your own vendor.
Don't shine the laser towards reflective objects - glass, metal,
etc. In general, don't wave it around like a light saber, no matter how
tempting that might be. Buy a green laser pointer (5 mW, class IIIa laser), and
wave that one if you want, but a class IIIb device is not for foolish pranks
like that.
When you're not using it to burn things, adjust the lens to
de-focus the beam. If you shine it across the room on the opposite wall and the
beam section is the size of a ping-pong ball at that distance, that means it's
de-focused and mostly harmless. Remember, the more focused the beam, the
greater the damage, so if it's de-focused like that the risk is greatly reduced
(but not completely eliminated).
NEVER LOOK INTO THE BEAM!!! Never, ever. Goggles or not,
de-focused or not, doesn't matter. If it's more powerful than a mere laser
pointer, do not look directly into it, ever. If it's a "naked" diode
without a lens that you extracted from a DVD writer, it's OK to watch it
directly for a short while, just don't bring it too close to the eye. But, the
moment you put a lens in front of it, it is forbidden to point the laser at the
eye.
NEVER POINT THE BEAM AT PEOPLE!!! It's rude, dangerous, and it can
get you in trouble with the law. Never point it at moving vehicles, airplanes,
or even houses, etc. - if there are people inside, don't point it that way,
it's that simple.
Don't let children play with a class IIIb laser. This is for
adults only. Heck, even some adults should not be trusted with something like
this. :)
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