Hey I'm Dave, welcome to my shop! Today in Dave's garage it's time to look at lasers and how they
work. And not just any old laser, because we're making the jump from RGB LEDs to directed-beam RGB
lasers, often known as show lasers. These are the ones you see onstage at your favorite concerts or
in larger clubs, and today we'll investigate how they work in detail as we put my new high powered
LaserCube Pro through its paces. The LaserCube is a fascinating and enigmatic device that
promises to revolutionize the way we think about color laser projectors. With its sleek, metallic
exterior, rugged constructions, and advanced capabilities, it's hard not to be drawn in by its
allure. What exactly is it capable of? How does it all work? That's what we'll find out today. The
finer points of this laser are fascinating, but even the basics can impress. As you might guess,
to make an arbitrary color of the rainbow it must combine individual elements of red, green,
and blue. But how do you combine three lasers into a single beam with perfect alignment? How do you
move that beam around to draw images? We'll look such challenges and how they solved them when tale
a look inside the beast. As a little kid I kept coming back to a singular odd thought experiment.
What if you had a sphere of glass made from one-way mirror, such that you could shine light
in, but it couldn't bounce back out. Ignoring inefficiencies and losses, could you leave it out
in the sun for a while to make a light bomb? Would the sphere flash if you broke it in the dark,
and so on? Think about it long enough, that eternal internal reflection almost leads you to
how a laser works, except we want all of our light going in a single direction. Let's imagine it in
2D for a moment, as a tube where, like my sphere, everything is a mirror on the inside. Except we
leave a hole open on the end, normally in the form of a partial mirror. Inside this cavity we
place a ruby rod aligned lengthwise. Then we wrap the ruby rod in the brightest lamp we can muster.
When we light the lamp, it emits white light in all directions. A lot of the light goes directly
into the ruby, and any that misses will bounce off the internally mirrored surface for another chance
at the ruby. Two things happen when the light finally hits the ruby. First, the incoming light
triggers a chain reaction within the ruby, causing many photons of red light to be emitted. Second,
the ruby somehow aligns all of that new light in a single direction. But why does the light come out
of the ruby in a coherent red beam? Well, Ruby is a crystal. And it turns out that Ruby emits light
mostly along its crystal axis when excited because of the way the ruby crystal is structured. Ruby
is made up of aluminum oxide with a small amount of chromium ions in its lattice structure. Those
chromium ions are responsible for the ruby's red color and its ability to act as a laser medium.
When a ruby crystal is excited with an external energy source, such as a flash tube, it causes
the chromium ions in the crystal lattice to become excited and move to a higher energy level. When
these ions relax back to their lower energy level, they emit photons of light. The specific energy
levels and transitions involved in this process dictate the wavelength of the emitted light,
which in the case of ruby, is mostly in the red part of the spectrum. So, the ruby crystal is not
just tinting the white light to another color, but instead, it is absorbing energy and re-emitting
it as a specific new wavelength of light. The crystal structure of ruby is such that the
chromium ions are oriented along a specific axis, known as the crystal axis. This means that when
the chromium ions emit photons of light, they tend to do so in a way that is aligned with this axis.
This leads to a highly directional laser beam that is emitted mostly along that crystal axis.
The key takeaway here is that the ruby isn't taking the white light and somehow aligning
it. It's absorbing the energy from the incoming light and using it to emit completely new photons
of a specific wavelength and a particular direction. It's more like it's eating all the
white light it can get and then pooping out little photons of red light aligned with the cystal.
Any emitted light that does come out in any other direction is reflected back into the ruby by the
mirrors so that it gets endless chances at aligning on the crystal axis. In the end,
it means that any light emitted by the flash tube ultimately comes out of the laser orifice
as a straight beam of red light. The amount that is lost to imperfect reflections or from hitting
opaque parts like the flash tube assembly is converted to heat. At the end of a day, modern
lasers are between 10 percent and 50 percent power efficient, meaning that if you put one watt in as
random white light, you'll get a half watt out in laser light. As a side note, by now you've
heard of the successful nuclear fusion test at the National Ignition Facility, or NIF. They focus the
beams of numerous powerful lasers onto a hydrogen fuel pellet and the energy from those lasers
ignites, or fuses, the hydrogen. They achieved more power output than the laser energy that hit
the pellet, a major milestone. But there's one problem: The lasers at the NIF are much older
tech dating back to the 1980s, and are only about 1% efficient. So, while the test was successful in
that it produced more net output energy than the laser energy that was pumped into the fuel cell,
it actually took up to 100x as much electricity to generate the laser light. In other words, the test
came nowhere near recouping the amount of energy put into the system as a whole; it only succeeded
in generating more power than the actual laser light hitting the fuel cell. It's a subtle but
important difference. The good news is that modern lasers would be up to 20 times more efficient.
With our basic ruby laser roughly understood, what about other colors? If a Ruby is red, how
do you make a green laser? Well, it turns out they generally use a "doubly-ionized neodymium-doped
yttrium aluminum garnet". Or as I like to call it, garnet. And for a blue laser, they typically use
gallium nitride. There are also tunable lasers that can shift their color output, but they're not
well suited to doing what we want to do, which is to make nright color visuals. The LaserCube,
then, doesn't contain a single full color laser - it contains multiple red, green, and blue lasers
that are aligned to produce a single beam of the desired color combination. But how do they combine
three separate lasers into a single beam without all kinds of convergence and alignment issues?
It turns out the answer to this problem is called a dichromic mirror. A dichromic mirror reflects
light of certain wavelengths, or colors, yet it allows others to pass directly through unchanged.
Also known as a dichromatic mirror or beam-splitter, it is essentially a type of
optical filter that reflects certain wavelengths of light while allowing others to pass through.
It is made by depositing thin layers of dielectric materials onto a glass or plastic substrate.
The unique feature of a dichroic mirror is that it has different optical properties for
different wavelengths of light. This is achieved by adjusting the thickness and composition of the
layers of dielectric materials deposited on the substrate, which creates a thin-film interference
effect. This happens when light bounces off both the top and bottom layers of the thin film. If the
thickness of the film matches the wavelength of the light, it will reinforce the light,
but if it's offset by half of the thickness, it undergoes destructive interference which cancels
out the light. For our purposes, a typical dichroic mirror used in a laser may reflect light
in the blue and green part of the spectrum, while allowing light in the red part of the spectrum to
pass through. This makes it useful for combining or separating different colors of light, allowing
them to be directed to different detectors or used for different purposes. Long story short,
you can control what gets reflected versus pass on through by controlling the thickness of the film
relative to the wavelength of the light color in question. Perhaps a diagram will help. Let's say
we have a green laser beam and we want to add, or combine, our blue and red lasers with it. We place
a first dichroic mirror at a 45 degree angle. The green laser passes through without change,
but the blue laser that we feed in at a 90 degree angle is reflected and directly aligned with the
green. We then use a second dichroic mirror, which this time allows green and blue to pass
while reflecting the red. The red is brought in at a 90 degree angle as well and it reflected along
the common path. Now we have all three lasers combined into a single path. From here on in,
it's point and shoot. And speaking of shooting, we need to address some basic laser safety. In the
United States, the Food and Drug Administration (FDA) regulates the use of lasers for medical,
cosmetic, and research purposes. The FDA classifies lasers into four different
categories based on their potential hazards to human health: Class 1: These are low-power
lasers that do not pose a risk of eye or skin injury and are exempt from regulatory controls.
This would be your typical laser pointer. Class 2 lasers are low-power visible lasers that can cause
temporary visual impairment but are unlikely to cause permanent eye damage. They are also exempt
from regulatory controls, because they figure your blink reflex will save you in time. Class 3R and
3B are medium-power lasers and can cause eye and skin injury. They require FDA certification and
are subject to certain regulatory controls. Class 4: These are high-power lasers that can
cause severe and permanent eye and skin injuries. They require FDA certification and are subject
to strict regulatory controls. Lasers that fall under Class 3R, 3B, and 4 categories require FDA
exemption or approval, depending on their intended use. The exemption is typically granted if the
laser is used in a controlled environment and with appropriate safety measures to prevent accidental
exposure or injury. The maximum safe power output of a Class 1 laser is 4 milliwatts. By comparison,
my LaserCube emits 2500 milliwatt, or 625 times as much as the legal limit for a class 1. That makes
it a dangerous class IV laser, capable of both blinding your vision and burning your skin.
You might think, "Oh, I'll just throw on a pair of laser protection glasses". But for which
color? After all, those glasses are designed to protect against a specific wavelength like red,
green, or blue. We have to be concerned with the entire visible spectrum,
but if you want a pair of sunglasses that safely blocks the whole spectrum,
you might as well make them out of wood because you won't be able to see anything anyway. You
might then get clever and throw on your welding helmet, but if it's auto-darkening, it will do
nothing to protect you when the laser hits your eye but misses the light sensor on the helmet.
Put more simply, there are no cheap and easy shortcuts to protecting yourself from a color
laser. Like a firearm, never point it at humans, animals, or anything you don't intend to shoot.
You must be careful about what's behind the target area and you must also avoid
any specular reflections that would hurl your beam right back at you. So before using a laser,
make sure that you read, understand, and follow all of the manufacturer's safety information.
This is particularly true if you need to take a laser apart and operate it with the case open.
Laser light leakage could damage your vision, and for that reason, rather than do it myself I'm
going to rely on some internal footage used with the kind permission of the Brainiac75 channel,
which I encourage you to check out for a lot more laser fun. With that, let's have a look inside of
a LaserCube. Here you can see the lid removed and a piece of paper set on top; as soon as the
laser is energized, we can see where dangerous light leakage would occur, and why we need to be
careful. As if protecting your vision isn't enough incentive, remember it can equally destroy your
camera's CCDs as well. The LaserCube model shown here has a single powerful blue laser, two greens,
and three reds. When it is energized, we can see the array of mirrors and lenses that are used to
focus and direct the beams. There is a lot of beam spread straight out of the laser diode,
and it's much more pronounced in one axis, known as the fast axis, and a bit less on the slow acis.
To correct this, each beam is first sent through a lens to gather that spreading light back into
a focused beam on the fast axis, and then a second lens to do the same for the slow axis.
A third lens collimates the beams into a straight coherent beam. The three red lasers are then sent
into a knife-edge array that reflects the three independent beams into what appears as a single
united beam. Similarly, the green lasers are sent through separate set of mirrors that bring
the green beam into alignment with the red. Finally, the blue laser emits directly into a
mirror that reflects it on though the output path. And since the green and red were reflected to be
in alignment with the blue, you now have a single beam of mixed colors. This complicated beam path
and combination array is possible only through the magic of the dichromic mirrors which I introduced
earlier. As you can see in this summary diagram, the three reds pass unimpeded through the first
dichromic mirror, while the green is reflected. The second dichromic mirror reflects the blue
while allowing the red and green to pass through unmolested, and the resultant beam is a fully
converged RGB laser. By adjusting the power of the various primary laser colors, the laser is able
to mix and match any color of visible light. This setup also avoids the need for manual convergence,
an annoying process that you might remember from trying to align the electron beams in an old CRT
or movie projector. I imagine getting this right takes some very careful alignment and tuning at
the factory, and it's not a product you'd want to drop very often... that much I'm certain of!
Knowing just what we've learned so far today would only get us a colored beam - a powerful
custom-color laser pointer, in essence. We want to move that beam around incredibly
quickly and to draw pictures with it. Your first thought might be to do what the yoke on an old
CRT does - bend the beam through electromagnets to place it where you want. Unfortunately, CRT yokes
are designed to bend an electron beam in a vacuum, not photons. Since photons do not have an electric
charge, they do not interact with magnetic fields in the same way that electrons do. Therefore,
a yoke from a television would not be effective at bending a laser beam of photons. Back to the
drawing board. The way the LaserCube actually aims the light is through the use of what are
known as Galvanometer Scanners. These scanners, also known as "galvos", are a common method used
to steer laser beams in laser beam projectors. They consist of two small mirrors mounted on
rotating shafts that are controlled by small electric motors or other actuators. To direct
a laser beam, the first mirror (referred to as the X mirror) rotates along the horizontal axis, while
the second mirror (referred to as the Y mirror) rotates along the vertical axis. By precisely
controlling the rotation of these mirrors, the laser beam can be deflected in any direction,
allowing it to be directed to different points on a screen or other surface. To approximate what's
going on, imagine you had two ping pong paddles with mirrored surfaces. You'd place one this way
and one 90 degrees to the first, and with a little practice, by rotating your wrists you could send
the beam in pretty much any direction you wished. Ping pong paddles are quite big and wrists are
slow, however, so the mirrors in a galvo system are typically very small and lightweight, allowing
them to move very quickly and with high precision. The stepper motors or other actuators used to
rotate the mirrors are also highly precise and can be controlled with great accuracy in software.
The beam emitted by the LaserCube Pro is 4mm in diameter. It has a divergence of 1 milli-rad,
or thousandth of a radian. The galvos in the LaserCube can draw at a rate of 35,000 unique
points per second. The higher the number, the sharper corners appear in the final drawing. A
slower or lazier galvo would need more time to draw the same result, so you would wind up with
either less resolution in the image or a longer time taken to draw it. The faster that the galvos
can draw the image, the higher the framerate and the less flicker you will perceive as well.
The LaserCube is controlled by a software package known as LaserOS. The software package includes
literally hundreds of different animations and effects, and you can combine them in creative
ways to create completely new shows. You can import images and songs and lay them out on an
editing timeline. You can download and experiment with LaserOS on any desktop or Android device,
and you get a color preview of what your results would look like even without a laser. If you have
an interest in tinkering with it, simply stop by LaserOS.com and download a copy.
Remember I'm mostly in this for the subs and likes, so please be sure to leave me
one of each before you go today! If you have any interest in matters related to autism, asperger's,
or ASD, check out the free sample of my book on Amazon, Secrets of the Autistic Millioniare.
It's got nothing to do with money and everything to do with how to live a successful life on the
spectrum. It's everything I know now about autism and ASD that I wish I'd known back then. In the
meantime and in between time, I hope to see you next time, right here in Dave's Garage.