I recently picked up this chinese-made laser tattoo removal device from ebay
now according to the specs this thing should contain a really scary pulsed
laser system inside and if so I'd love to screw around with it when it comes to
wacky eBay gadgets like this you never know what you're gonna get. for one
sellers often blatantly lie about the ratings, and two this entire system cost less
than having a doctor burn off a tattoo, so it's not like you're can expect
some state of the art medical system. now that being said, I'm not super concerned
with how safe or effective this thing is because honestly I just wanna blow some
stuff up with a pulse laser. in fact, if this thing can produce pulses of say , I
don't know like a million watts I'll be pretty impressed, and if not I'll have to give
it some much-needed upgrades. so yeah without further ado let's fire this
thing up. so uh, spoiler alert. this thing packs some serious firepower. see all
those little marks in the screen? this thing is so powerful that blew a bunch
of holes in my camera's sensor without even taking a direct hit.
what I'm getting at is that this thing definitely isn't a toy and as tempting
as it may be I do not recommend buying one of these things. dangerous is an
understatement for this laser and if you don't have some high-end laser goggles
you'll go blind using this thing. so yeah please don't try anything you see in
this video at home alright so here's what all came with his unit. you got the
laser head here and the main power supply I got these treatment specific tips that
actually might be able to change the lasers output color. you got this
really mysterious ointment, this funnel for adding cooling water, a foot switch and
then these these really sketchy laser goggles. this manual here, if you could
even call it that, turned out to be completely useless for assembling this
thing, but luckily putting this thing together was really straightforward, like
honestly a ten-year-old could assemble this thing, and I'm not totally sure that's a
good thing. I went ahead and used deionized water
for the cooling fluid as it turns out that ultra pure water is actually a really
really good electrical insulator. pretty cool right? now before I power up the
laser I need something to protect my eyeballs
because from what I hear, permanent blindness is a bummer.
now the hilarious thing is that the goggles that came with this unit are the
complete opposite color of my own goggles that are rated for a YAG laser
like this. I don't know about you guys but I feel like this could be a huge
issue so I'm gonna play it safe by wearing these things. now unfortunately I
don't have any visible tattoos that I can burn off for this video luckily this
is an all-in-one device. it can also remove eyebrows, remove
birthmarks, freckle, and then uh whatever black doll is. my eyebrows probably could
use a little bit of taming, but you know what before I start pointing this thing
at my face, I better test on something like this piece of metal over here. all
right I got the energy maxed out here we go oh my gosh that is loud
it's literally blowing craters in the metal .that is a lot of damage
check out those insane plasma fireballs
the surface must be getting incredibly hot. I was not expecting this thing to be
so strong especially out of the box
like that's just blowing craters in the metal with nothing but light like that's
insane!
this thing packs some serious power. right here I have a two and a half kilo
chunk of tungsten. let's see what happens when I hit it with the laser.
in case you don't find these little craters impressive
tungsten has a melting point of over three thousand four hundred degrees
Celsius the highest melting point of all pure metals. now I wouldn't 't even be
surprised if the center of the fireball is hotter than the surface of the Sun. I
know what you're thinking, what happens if you get hit by the beam? well one way
to find out I guess oh wow it kind of tickles well I mean
yeah it hurts but not nearly as bad as I was expecting
that's actually pretty neat. now the reason it's not leaving craters in my
skin is the fact that my skin just doesn't absorb this light very well. now
this is especially useful for removing dark tattoos, as the laser selectively
destroys the dark ink while leaving the skin untouched. well sort of. as an
example of this, let's pretend I've made the biggest mistake of my entire life
and the only way for my family to love me again is to get it burned off. well
lucky for me, this is just another day at the office for this laser
well that sucked I mean yeah it erased the ink and actually did a really
good job but maybe maxing out the power wasn't the best idea here
ah whatever my skin will probably heal. now unfortunately burning off a tattoo
isn't always so simple. for one my pale skin and dark ink make selectively
destroying the ink a lot easier. but the thing is lasers are racist! I mean those
with a darker complexion are a lot more likely to receive burns
because their skin absorbs more of the light. and this isn't even the
only complicating factor, I mean tattoos come in a huge variety of different
colors you can't use just one laser for all of them. as an extreme example of
this I've tattooed these two boards here. now when I try to remove the one on the
darker board it's hard to prevent destroying the surface along with the
ink. but even on the lighter board I run into issues. now the dark ink comes off
pretty easily but the red ink is essentially untouched so now what do we
do? that's where this witchcraft comes in. so inside this tip is a crystal of
potassium titanyl phosphate, or KTP for short. it splices two IR photons together
to make one green photon via a process called second harmonic generation. now
the fact that you can just screw this on to the tip to make it green is literally
insane because it's usually a lot harder to pull off nonlinear optical processes like this
the green light does a much better job at removing the red ink, but really
this isn't much of a surprise since red and green are on opposite sides of the
color wheel. okay so it works on wood but how about skin? uh one way to find out oh
oh holy heck that hurt! it turns out a lot of things absorb the green light
better, and then includes my skin! so sorry guys but I'm gonna have to pass
on lasering this one off. I guess it's permanent now. oh yeah rubbing alcohol is
a thing isn't it? so what else can I do with the green
beam? well how about cleaning some dirty coins
oh wow look at that good as new! the polka dots give it an added touch
don't you hate it when you transformers get all rusty?
luckily with this laser you can burn the rust right off. oh wow that's amazing I
didn't even need to use corrosive chemicals just an unimaginably dangerous
laser. aluminum foil reflects all but just a few percent of the light that
hits it, so is it possible that we can shoot through it anyway? I guess so! well
that's actually pretty crazy because remember that's just light that's
shooting through the foil. if we look at it in slow motion, you can see little
pieces of burning aluminum flying off of the metal so that's actually pretty
neat. oh yeah see all those little spots in the picture? this is when I noticed
them too. ah heck. turns out that even without a direct hit, the laser still managed to
blast a bunch of holes in the camera sensor and since there's no fixing that, I
might as well keep lasering stuff until the entire sensor goes blind. this one
was suggested to me by youtube user Vidduley and it's just a block of clear
acrylic. now even though it's nearly transparent it can still burn
its entire beam path into the plastic. now it's funny because I tried using
this effect to engrave stuff in the acrylic but I just ended up vaporizing the
surface of my table behind the block. a balloon seems like a silly test compared
to everything else but check this out
well that was surprisingly difficult what gives? it turns out that the hot
plasma formed on the surface ends up absorbing most of the laser pulse energy
this actually protects the material behind it somewhat. this is why military
laser weapons are almost never pulsed. when it comes to burning stuff with a
powerful laser it's hard to find something easier to set fire to than a
match. but this is a pulse laser so it doesn't behave like you'd expect
in fact the laser obliterates match heads without even igniting them. I think
the explosions at the surface must be too violent to allow a stable flame to form
hmmm I wonder if this laser can burn a CD? oh yeah punches straight through it
even if I flip it to the shiny side it still vaporizes the metal coating. that's
pretty crazy oh yeah I can't forget about these
goggles that were sent with the kit. surely the sellers care about our
safety right? huh look at that. yeah that's right, your retinas would look like
a slice of Swiss cheese if you trusted these things. big oof for those who
bought one of these kits and used the included goggles. look what happens if I
don't point it at anything. oh yeah the air ignites! think about just
how crazy that is. air, which is basically transparent, is
exploding in the laser beam. if you want to light the air on fire with nothing but
light, you need some gigantic power densities. in fact the threshold is
something like 300 billion watts per square centimeter. now that gives us a
lower bound on power density but what's that say about actual output power? the seller
claims that this laser outputs a max of 2 joules in each 10 nanosecond pulse. now
2 joules may not seem like a lot of energy, but when it's dumped in just 10
nanoseconds, you're talking peak powers of 200 million watts! but let's just
pretend like the seller is a total liar. how do we measure the output power
ourselves? well it's not as easy as just pointing it at a meter, as it turns out
that most sensors just don't like eating mega watt class laser pulses very well
that being said we can get a pretty good estimation using just a tiny bit of math
calculating actual power from the power density means that we need to find the
minimum size that the laser can focus down to. now this is difficult for me to
measure directly, but we can use the fact that lasers tend to take on a Gaussian
beam profile in order to make some estimations. in the simplest case you
have a wave traveling along Z and polarized along X that takes on the
fundamental transverse mode of the laser resonator. now when this happens the
time-independent electromagnetic field looks approximately like this. now if
you're thinking oh wow I'd rather stab my eyeballs out than try working with
that, well you're not alone, but actually it turns out that the special mathematical
properties of the Gaussian function mean that these beams can be described
with just a few simple parameters and then manipulated with simple algebra
I started by measuring the beam divergence and then calculated the waist radius
using the laser's wavelength' and this gives a diameter of approximately 10
microns. now equating a beam of this size to the
minimum irradiance required to ionize air gives a minimum laser output power of a
hundred and fifty thousand watts. but the thing is, there's no way that this thing
is operating even close to the perfect Gaussian beam, so if it's say ten times
worse with a hundred micron beam diameter, well that gives an output power
of fifteen million watts. and now this seems crazy, and it's actually several
times higher than the instantaneous electrical power draw of the entire town
that I live in, but it is actually reasonable. all right so I have a pulse
laser with output the megawatts. now blowing stuff up is always gonna be fun
but what else can I do with it? well how about using it to build a laser
pumped laser? there's a lot of ways to pull off laser inception by using one
laser to drive another, but today I'm feeling old school and I also want to
play with some chemicals. Here I have an assortment of organic dyes, some that i
synthesized years ago and others that i bought online. now under the right
conditions, these dyes can be used as a laser medium that can output a huge
variety of colors. oh wow this brings me back to my time in academia! well this
does at least. I'm not exactly throwing a party though, I just need to make some
solutions of these dyes in ethanol. these dyes are extremely photoactive so
a little goes a long way here. in fact I only need something like 50 milligrams
per 100 milliliters of solvent and even this may be too much so I'll probably end up
diluting them. now a precise concentration isn't super important but
too much dye in the solution will kill the output. I started by filling a
cuvette with rhodamine B dye solution diluted to about 10 percent of the
original now placing the cuvette directly in the beam path does give some
colorful light but I can't be sure that this is actual laser emission. by kicking the
cuvette off at an angle the green laser beam is refracted through the cuvette so
that it doesn't line up directly with the potential dye laser beam. now sure enough
this reveals that the liquid is actually operating as its own laser as there is now
an orange beam exiting at an angle to the original pump green beam. now that is
pretty cool. since there's still so much green light left exiting the cuvette i
upped the concentration to utilize more of the pump light and this actually
dramatically increases the output. I found the best results using about a
half a millimolar of rhodamine B. now notice that I'm not using any sort of
external mirrors to act as an optical resonator. in fact the roughly 10%
reflectivity of the cuvette walls provides enough feedback to achieve a
massive amount of optical amplification. now that's a material that likes to lase!
since the reflectivity is the same on all sides of the cuvette you get laser
emission from each side of the cell, with one face typically favored stronger
than the others. now of interesting notice is the presence of the side beams
running 45 degrees to the main beams. now it turns out that the corners of this
square cell act as strong enough retroreflectors to form laser cavities
here too, thus forming this beautiful but terrifying laser star of insta blindness
sticking a mirror on one end causes the majority of the dye laser output to exit
in the opposite direction, giving some sort of controllability. still though I
wasn't comfortable viewing the output in person as the peak power is still very
high and my goggles don't even block this color. this is a real bummer too
because orange lasers are very hard to come by. in terms of peak output power
this laser tattoo removal system is actually the most powerful laser that
I've shown on this channel, so what exactly is inside this beast? I tore down
the main unit to see what's inside and it's actually pretty simple. so you have some
control circuitry over there you got a water pump and water cooling reservoir
a switching high voltage power supply then an energy storage capacitor
right here which supplies energy to the pulse laser. now notice there aren't any
optics in here. in fact the entire laser cavity is contained within the handle
tearing this down reveals that the laser inside is old-school
it's actually quite similar to the first laser ever built. there's a flash lamp
here that pumps light into a crystal of neodymium doped yttrium aluminum garnet
or Nd:YAG for short. this energizes the neodymium ions in the crystal and
sitting between these two mirrors here allows it to operate as a laser.
as a sidenote Nd:YAG was one of the first laser media ever discovered and
it's still widely used today so it's actually pretty cool that it survived the
test of time like this. there's a special optic that's inside of the cavity here
which allows it to produce such absurd pulse powers. now initially it absorbs the
light coming from the crystal which actually kills the laser output, but what
this does is it allows the crystal to build up a bunch of energy while the
flash lamp fires. but after the optic absorbs enough light it suddenly becomes
transparent, effectively exposing the highly energized crystal to the cavity
mirrors. now this causes all that energy to get dumped in an incredibly short
amount of time, limited by the time it takes for the light to make a few
bounces through the cavity. now this process is called q-switching and
doing it passively with this little optic is probably the simplest method in
use. when this q-switched laser fires, pulses have a duration of about 10
billionths of a second which means that light only
travels about three meters during this time. to put that in perspective, pointing
a laser pointer in the sky for one second will produce a pulse that is
300,000 kilometers long. it's really hard to fathom timescales this tiny but
amazingly there are already lasers that run over 10 million times faster than this
so now that I've gone through the trouble of tearing it apart is there
anything I can do to make it stronger? well removing the q-switch would
actually increase the energy a bit but that's at the cost of a dramatically
decreased peak power. in fact if I want to increase the output my best bet is to
feed more energy to the lamp. looking at the energy storage capacitor I see that
it's rated for 1,400 volts at 100 microfarads. when I actually measure the
live voltage through a voltage divider I see that it only gets charged to a max
of about 800 volts, or only about 1/3 of the energy that it's rated for. as a side
note using this measurement as a way to estimate peak power actually gives a
similar result to the one I got earlier but this time I get about 30 million
watts. for funsies I used this number to calculate the
strength of the electromagnetic field at the beam waist and as expected it's
insane. look at that, an electric field of over billion volts per meter, that's
hundreds of times stronger than what the accelerators produce in the Large
Hadron Collider. now granted that's over a tiny distance but it still shows the
potential of lasers in desktop particle accelerators. all right so back to
modding this thing. so I guess I have two main options here to increase the
output. I could crank up the voltage feeding the capacitor, but since the
impedance of the flash lamp is nonlinear, a higher voltage would mean a shorter
pulse length and that would disproportionately overpower the flash
lamp. my guess is that charging the cap up to its full rating would annihilate
the lamp in one shot. so I guess my other option is to add more capacitors this
will definitely increase the energy but will be done more gently over a longer pulse
I went ahead and added enough capacitors to triple the energy in the circuit so
without further ado let's test this thing out. all right here we go
that was bad. did it just break? it broke! it turns out that some
underpaid grad students in the 60s came up with these empirical equations that
describe the lifetime of a flash lamp with its drive energy. in fact there's a
dramatic relationship here, to the power of eight and a half actually! that means
that tripling the drive energy for given pulse length will actually destroy the lamp
about 11,000 times faster than running it at its original energy, so it's no wonder
that the lamp exploded. as a sidenote pretty much all the laser science in
this video can be found in this book from 1976
I learned a bunch from it when I first read it four years ago and the info is
still just as relevant today. now for those out there who are interested in
experimenting with old-school flashlamp pumped lasers you'd be
hard-pressed to find a better resource than this. well I hate to have such an
anti climactic ending but I think I've destroyed enough of my equipment for one
video. but seriously I obliterated the Sony camera that I just bought last year
and I even put a few more holes in this camera that I'm shooting with right now
now including the tattoo laser that I destroyed this was by far my most
expensive video yet. now luckily I have some dedicated patreon supporters that
kept supporting me even when I can't upload very frequently so as a thank you
to you guys, imma let you guys see this video first before I make it public
anywhere else. so yeah a big thank you to you guys. one last thing. so even when I'm
not uploading to my channel I'm usually posting content to my other social media
so be sure to check those pages out via the links in the description
I especially recommend watching the most recent video my backup channel of an
amazing lightning storm I experienced while tornado chasing
plus to all the makers and home experimenters out there I highly
recommend checking out my discord server as there's a ton of knowledgeable
members there and they're always working on awesome projects. so yeah until the
next time stay safe and happy lasing!!!