Potentials - January/February 2016 - 31

easy source of adjustable current or
voltage regulation. They can be used
to dump 1.5 A of current and can be
paralleled together for more current
output. I always keep a pile of these
on hand because they are cheap and
easy to use and can effectively power
laser diodes. Unfortunately, they are
not very efficient, and heat up a lot
when run at high currents, but it was
a reasonable option nonetheless.

fig5 The finished laser shotgun.

the power going to the laser diodes
would change with both the dropping voltage of the draining battery
and the rising forward voltage of the
heating laser diodes. Buck converters are commonly used in hobbyistbuilt handheld lasers, as they allow
efficient power transfer from the battery to the laser diode, while keeping
power losses by the driver to a minimum. This was the idea I wanted to
use, so I contacted the seller of my
favorite adjustable buck drivers for
an order. There were none in stock
at the time, but the seller told me he
would have more before long.
A couple weeks passed and still
no buck drivers were available. Unfortunately, I was in a time crunch,
as I was starting a research internship in just a few days and there was
no way I could operate a 40-W laser
in the apartment in which I would
be living. It just killed me knowing
that I had nearly all of the parts I
needed on hand, yet I was going to
have to wait until my next break at
the end of the summer before tackling this project. Then I realized I
had another option: the good oldfashioned LM317 regulator.
LM317 regulators are known and
loved by hobbyists all around the
world for being able to provide an

fig6 The laser's incredible beam in a
dark room.

some assembly required
Then the construction began. Each of
the laser diodes in the bank was powered individually by its own driver.
Each driver consisted of three LM317
chips strapped to a heatsink, where a
large 1-X power resistor was used as
the reference resistor for the chips.
This configuration provided 3.75 A of
current to each laser diode. I ripped
apart an electronic airsoft gun,
stripped it of most of its parts, and
placed a high-current-rated momentary switch behind the trigger mechanism to allow for the laser to be operated by pulling the trigger.
I hooked up all the circuitry and
then started crudely securing the
parts. I attached the drivers to the
casing of the gun by driving screws
into the gun's plastic casing, and
the diode bank and heatsink assembly were held down with a bunch of
windings of wire. I cut grooves in the
gun with a hacksaw to fit large focusing lenses, and those optics were
then secured with some tape. The
gun could have been built a lot prettier, but this way worked and that's
all that mattered (Fig. 5).

Packing heat
Now I had an incredibly scary device
in front of me, and all that was left
was the testing phase. I grabbed my
laser goggles and headed to the
garage, where I nervously attached my
LiPo battery and pulled the trigger.
Even through my goggles I could witness this device's sheer power. I pointed it at a cardboard box a few feet
away, and it started smoldering
immediately and even caught fire after
a few seconds. I began laughing as
any mad scientist should when witnessing their crazy invention unleash

fig7 A still image from my YouTube video,
"My Homemade 40-W Laser Shotgun!"

its destructive force. I had built a
impractical and highly dangerous toy
solely for the sake of lighting things on
fire in an unorthodox fashion.
These initial tests were with the
unfocused raw beam of the laser. I
then experimented with different
lenses, allowing me to converge the
eight beams much like a choke does
to a shotgun blast. At the focal point,
the power density is ridiculous, and
the converging beams can even ignite wood and plastic.
As attempting to view the output would severely damage my eyes,
even without a direct hit, I grabbed
my camera to witness the beams.
The amount of light that comes out
of this gun is beyond belief, lighting
up my entire garage like daylight-
except with blue light. On camera, it
looks as if a lightning bolt is coming
from my hands (Figs. 6 and 7).
I was pleased to push the limits
of insanity with a project like this,
as not only does it help me appreciate what scientists and engineers
have worked so hard to develop, but
it also serves as a reminder as to
why science is awesome! This project surely is not the last insane and
impractical laser device I will build,
and I'd like to see if crossing the 100W mark will be possible before long.
Until then, I'll continue entertaining
myself with crazy science projects.

about the author
Drake Anthony (drake@styropyro.
com) is a senior at Southern Illinois
University, where he is double
majoring in chemistry and math. He
plans on pursuing his Ph.D. degree
in physics after finishing his bachelor's degree. He is known for his
YouTube channel "styropyro," where
he posts videos of his laser and science projects.

IEEE PotEntIals

Januar y/Februar y 20 1 6

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