Fiber Laser Learning Lab 21 Bubble Marking Clear acrylic

[@rajivlaroia1441]

Since the refractive index of acrylic is around 1.5, when you put the focus inside the acrylic by what you think is 5 mm, it is actually more like 7.5 mm. This is because of the bending of the rays at the surface that causes the focus point to move deeper inside. It is a somewhat similar to the water in a pond appearing shallower than it is. So when you think you put the focus at the bottom surface (where the steel sheet is) it was actually much deeper so the steel was considerably above the focal point and did not get marked well.

[@Irosado65]

I enjoy (dare I say love) your methodical explanation and thought possess. Its refreshing to hear you put your thoughts into word that I can understand. It feeds my inquisitive mind!😄👍

[@SarbarMultimedia]

In th 2 years since I did this video , I have come to understnd a lot more about jow lenses work with laser beams. It is far removed from the basic lens theory that everyone from the Ancient Greeks to modern day lense manufactureres trust in. Whether it be F theta lenses that are used for galo heads or simple plano convex lensed used in CO2 machines they are all designed as thigh our machines were telescopes or cameras etc, they are designed to focus NORMAL light images. Anyone born before 1965 will never have imagined the weird concept of a coerent (laser) beam of light. We are not trying to transmit images with our laser beam we are exploiting one of its properties , the Gausisian INTENSITY profile, and require a lens to focus coherent INTENSITY not the usual non-coherent light all around us. My CO2 laser as well as this fiber laser were continually exhibiting demonstratable anomalous properties I could not understtand. When I decode hoow lenses work withh my CO2 machie it was onntt a siideways step to explain fully what these "bubbles " were and how /why they are created. The nominal manufactureres focus for the F-theta lens is set to the mataerial surface , that is the OPTICAL focus and not the INTENSITY focus. The INTENSITY focus where maximmm material damage occurs could 4 or 5mm below the surface. At 1 micron wavelength acrylic is about 10% absorbant (90 transparent ). This means that very few light rays will hit an solid materia (atoms) they will pass through unobstructes. However ther will be (on average) about 10% of rays that will hitsomething solid. Thus if that INTENSITY focus hits somethiing solid (an atom or two) it will transfer its energy as heat and there will be an instantaneous change of material to a vaporised state That gaseous state is contained in a solis block of acrylic but is sufficientlt explosice that it can cause a small fracure witin the material that under a microscope looks a bit likea spiral galaxy. So they are not reallt bubble but lots o frandon micro shear planes as an intensty focos meets a molecule. Best wishes Russ

[@ahmedvawda1282]

You’ve answered a burning question of mine, namely to mark polycarbonate. The material used in 3M safety goggles.

[@SarbarMultimedia]

Hi Damaging ANY material depends on two key factors. 1) The resonant frequency of the material's molecular structure and 2) The stimulating frequency (wavelength) you fire at it.. 1)The stucture of a molecule is best imagined as a metallic scaffold stucture. Just a few 6m long scaffold poles built into a cube will be a very "wobbly" structue. If you stand by the cube and push/pull it to create an oscilation you will note the very low frequency required to do so. IF you now try to shake it at ten times the frequency , the structure will ignore your attemps to add kinetic energy. Add diagonal cross bracing tubes and the stiffened structure again resists your low frequency attempts to add kinetic energy.Take this simple cube stucture and make the tubes just 1m long. I am sure you can visualize how such a "stiff" stucture will again ignore low frequency stimulation. 2) The very wide terahertz frequency range of the mangetic spectrum is responsible for stimulating virtually all materials . (see en.wikipedia.org/wiki/Molecular_vibration ) and you can see what the wavelengths this equates to from this diagram www.geeksforgeeks.org/applications-of-electromagnetic-spectrum/ This diagram for polycarbonate shows the efficiency with which various wavelenghs shake the molecules and add kintic energy. 100% transmission means that zero energy has been absorbed. Because about 10% energy is absorbed at around 1micron wavelength you can MARK but not CUT . At CO2 wavelenths (10,640nm) the absoption is 100% (transmission 0%) and why polycarb safety glasses are safe. www.researchgate.net/figure/The-transmission-spectra-of-the-05-mm-thick-polycarbonate-plate-reproduced-from-Ref_fig2_345435824 The same diagram can be applied for acrylic (PMMA) . However acrylic is damaged by a completely different mechanism to polycarbonate.Acrylic liquifies at 160C and boils at 200C there is no chemical reaction required to cut acrylic, it is just a change of state that requires a lot of energy. At 1micron wavelength because the absorption eficiency is so low (5 to 10%) the photons in the laser beam have a low chance of hitting a molecule and it has to be a focus of photons occuring that can createb enough energy to vapourise an acryic molecule. It is this random( but focal zne effect) that causes internal vapourization (explosions) with in the acrylic material. Polycarbonate is different in that marking occurs at 1 micron wavelength as a result two effects First, the low energy absorption into the surface of the polycarbonate causes local surface melting an micro boiling. This in turn changes the light transmission properties at visible wavelengths and effectively creates billions of micro cats eyes that reflect normal white light, This is how you percieve "maring" of the material.the material. Playing with the power and exposure time (speed) creates a range of surface textures and hence different colours. For example it is possible to creat a gold colour from white polycarbonate.

[@razvandumitrugrecea9388]

Hello Russ I finished your series on fiber and I'm impressed how you correlate things, on the other side this software that you use its minimalist and its offerings control on basic marking. I worked on Rofin Sinar CombiLine RT,marking Day and Night on polymer vlm software that they give to you it's really impressive and helpful with some functionality like displaying overlapping percentage,the spot diameter,galvo head speed,first pulse suspension in real time,another thing I want to add on the color marking and you could take it like a tip is to use repetition on hatching (1 to 2),use offset on line width,on power add one amp and scale 100 mm/second,use lower galvo speeds for contrast (radian/second) Hope to see more labs one this fiber guide 🙂

[@ishaqmuhammad7848]

Hello sir I need your phone number I like to discuss very Important thing please if you don’t mind Thanks Ishaq

[@owjawelhoor]

Hello. Im using the fiber laser on glass. First i add white marker on the glas. Than i run 4 passes over it, take off the marker. And than you have a light mark in the glass. Its nice for names and logo’s.

[@closetpicker]

My guess is that the acrylic itself isn't pure enough, and has tiny impurities within it that the beam acts upon

[@newmonengineering]

Interesting, i wonder what would happen if you sand one side so its not clear any longer and then test the sanded surface on the bottom and top and see if the refleaction from the bottom comes into play or of it can even mark below the sanded surface. Its pretty interesting that it makes bubbles at random, and not very uniform in depth.

[@SarbarMultimedia]

hi In the past three yearsI have learnt a lot more about the interaction of light waves with various materials and I now understand how this effect happens. In fact I recently reproduced the same bubble effect during experiments with a diode laser see kzbin.info/www/bejne/pqexfJloiZKippY from about 20 minutes The bubbles are random (ish) because there is a zone of light intensity either side of the focal point which is sufficient to ineract withthe few acrylic molecules that happen to be in the path of the photons

[@precisionlasersolutions7996]

I can see you quite liked that, but what was noticeable on yours was that the bubbles were quite spread out, 5 or 6mm for the densest area, I think with a little more playing you could squash the dense area to 2mm ish, it makes the lettering stand out a bit more.

[@SarbarMultimedia]

As with all the things I play with and explore, I am less interested developing a final professional application but rather more interested in understanding the physics and chemistry basics behind the observations I make.,Yes there seem to be dense areas both above and below the focal point where some sort of light interference pattern id taking place. With the 10.6 micron CO2 wavelength. the light energy never has a chance to enter acrylic. Instead there is an energy transfer at THE SURFACE as those exposed molecules become excited, heat up and disappear as vapour. That is why acrylic is a fantastic tell-tale material for "seeing" energy intensity patterns and velocity variations. Because 1 micron light has no such stimulating effects on the SURFACE molecules, it appears that this shorter wave length light psses through the acrylic molecular struture without exciting any of the molecules. I say "appears" because my observations tell me that acrylic molecules ARE being excited by the 1 micron wavelength light but not sufficient to achieve melting or evaporation.. This was proved when 90% or more of the light intensity never made it through 25mm of acrylic to damage a stainless steel surface That energy MUST have been absorbed and generally heated the acrylic to some low level. The second critical observation arising from this asks what is happening to the light energy at minute and random points within the BEAM (not the material) that is causing local spikes of molecular excitement within the material. Again the material is only showing us that something weird is happening to the light. This is like nature's slight of hand . Ignore what you see (those fascinating "bubbles") and look at a more fundamental phenomenon taking place in the background.. Note that there is a pattern of bubble density above and below the focal point but not AT the focal point. Doesn't that seem strange?. You would naturally assume (based on all normal lens and wave theory) that maximum material damage would occur at the focal point. The fact that it doesn't. is the REAL puzzling outcome of this exploration, What on earth is happening to the light intensity at these "nearly focused " zones . As I have declared many times, I am neither a physicist or chemist so my superposition theory of intersecting lightwaves is the best I can offer by way of an explanation. I am sure there is a doctorate waiting for someone who investigates this phenomenon. So even at 1 micron wavelength, acrylic is demonstrating its "tell tale" ability........if only we could read the message in those bubbles Best wishes Russ

[@leovuyk]

very interesting ! by the soot effect.

[@sherlockhomeboy4031]

Ph u look cool today my boy

[@DoRC]

Is this how they burn pictures into the center of acrylic cubes?

[@SarbarMultimedia]

No That is a complete;y different process where they use TWO laser beams that use light at about 500nm wavelength and the position in space where they intersect is where a micro bubble is formed. I is often done with special crystal glass but latterly they use a special clear plastic doped resin. If you look at my answer to Precision Laser Solutions comment you will find that the fractures (bubbles?) within the acrylic are symptomatic of a much deeper mystery . Best wishes Russ

[@lindaxtlaser6104]

Yeah, very beutiful! We also produce this fiber laser marking machine and other laser machines.

[@scabskunk]

Acrylic can absorb water over time. Maybe it has absorbed some and the water is vaporizing inside it? Would be interesting if you could maybe put a bit of acrylic in a dehydrator or a brand new batch to see if it still happens.

[@SarbarMultimedia]

Hi If you watched earlier videos you will have seen that I can mark metal through 30mm of water plus 3mm of glass in the bottom of the container. I therefore think water is even less receptive to being excited by 1 micron wavelength light than acrylic was supposed to be. Water absorption is possible but only to about 0.5%. The material I used was from a large sheet and was covered in plastic film until just before this test. One observation that you may have missed is that most of the internal fracture planes are BLACK. Steam is not that colour. It requires incredible forces to break hydrogen and oxygen apart (electrolysis) and there is no carbon involved. whereas when you OVERHEAT PMMA (C5O2H8) you get mono methyl methacrylate vapour which on further heating breaks down to combustible molecules and if you notice the close up shots of the reactions inside the acrylic you see flashes of light (combustion). The real problem with what you are observing is NOT the effect but WHY the effect? Thanks for the comment because anything that can stimulate a discussion on this subject may help confirm what is actually happening. Best wishes Russ

[@WilliamShakour]

Are you tempted to try the substances you tried on the wood? Sure they will not soak into the acrylic, but when the water dries the salt might have some effect.

[@SarbarMultimedia]

It is a definite possibility that I will quickly try. I say quickly because there is a backlog of orders at Lotus Laser and they have a customer that wants to buy the machine they have lent me. So it looks like the end for the current fiber laser adventure. I'm sure it will not be long before they replace it with something else that they do not fully understand. Thanks for the suggestion Best wishes Russ

[@WilliamShakour]

@@SarbarMultimedia I am so sorry to hear that... I was looking forward to more great videos on the subject. Still... onward! Will keep watching... thanks for all the great, informative and entertaining content.

[@russellspear4911]

Refractive index is coming into play

[@SarbarMultimedia]

Refractive index is in reality a way of defining how much light slows down in a material. Please explain in detail how you think that a property that is UNIFORM within the material can produce VERY local and random hot spots of light energy to locally chemically change the material. best wishes Russ

[@maksimsoft]

Perhaps the laser beam, reflected from the metal, changes (increase) the wavelength. Or the engraving process generates infrared waves that act on acrylic.

[@SarbarMultimedia]

You have not watched far enough to see that even when I remove the reflective surface the effect still happens. My first thoughts were reflective interference effects but I soon disproved that. Best wishes Russ

[@maksimsoft]

en.wikipedia.org/wiki/Bubblegram

[@SarbarMultimedia]

@@maksimsoft Yes. I am very aware of that expensive technology that requires the intersection of two separate laser beams plus some special optical glass or special optical plastics. They also run at about 500nm , half the frequency of the fiber laser I am using. The effect I see may be similar but it is is totally random and I believe it arises from the wave interference within a single focused laser beam (not even at the focal point) and not the controlled interference of two intersecting laser beams. Best wishes Russ

[@shadowmite]

Interference between the original refracted beam and it's reflection from the bottom surface (exit aperture)? Try angling the bottom surface to bounce away from the medium?

[@SarbarMultimedia]

Hi Can I point out that this testing was not carried out under the central axis of the machine (rewatch from 2min 15sec) and therefore the beam is already angled to both the top and bottom surfaces of the material and as the scanning of the text takes place that angle is continuously varying. For internal reflection to take place you will need ray angles much greater than I was using. Thus I think my method has already provided the answer to your question.. Thanks for the comment because this is a fascinating puzzle that I can demonstrate but have not established any factual explanation for. Best wishes Russ

[@matthewfogle2280]

@@SarbarMultimedia I forgot about that, ok so you already have interfering beams in the acrylic bouncing around. Can you safely test on axis right down the center where the known reflection point would be halfway? (This is still shadowmite, somehow I have two accounts here).

[@SarbarMultimedia]

@@matthewfogle2280 Hi Matthew. One thing you mentioned , refraction. is having a significant effect on one feature.....the focal point. I nominally set the focal point at the BOTTOM surface of the material but refraction will have shortened this by some unknown amount. Worse than that. the aberration inherent with this lense means there are multiple focal points for the beam depending on the diameter of the beam Furthermore, the light intensity at each of those focal points will be in accordance with a Gaussian distribution. This is no simple problem to decode. Observe the scatter pattern of damage carefully and understand I am working away from centre so my beam entry angle will be 3 to 5 degrees, Why is my scatter pattern not canted at 3 to 5 degrees? Lots more questions than explanations with this problem. Best wishes Russ

[@WaffleStaffel]

At 40:38 it's most noticeable, but I keep seeing it in other runs... Is it just me, or is the word "BUBBLES" actually legible from the side, even though there's no apparent reason it should be?

[@SarbarMultimedia]

Hi If I screw up my eyes and stand on my head I can sort of see what you mean but there is no logic for it to be seen from the front. Best wishes Russ

[@jtcustomknives]

I’m at 14min in and before I see your solution I’m going to toss out possible impurities in the plastic. Something kinda like how you marked the wood.

[@mikaelludwigsson]

Nice video. But you have to replace the battery in your watch :D

[@SarbarMultimedia]

The clock on the wall helps me to stay young!!! Best wishes Russ

[@curtisoliver1006]

Nothing is a perfect material. Acrylic has a high transmittance, but if you put a high enough power density laser through it. Even with low absorption it will eventually reach the threshold. In this case however it could be natural defects in the acrylic responsible for breaching the threshold, by lowering the transmittance.

[@SarbarMultimedia]

Hi Curtis I have since done more research to see if I could account for this phenomenon. Several people have suggested micro dust particles inclusions or as you suggest defects in the material. As you say, although the vast majority of the material is transmitting the light it only needs a slight local change in homogeneity to change its light absorption properties. This results in very local heating which in turn changes the material refractive index (thermal lensing) and produces a further local energy concentration/ micro point heating effect. May be worth doing some reading on this interesting subject Thanks for the comment Best wishes Russ

[@curtisoliver1006]

@@SarbarMultimedia Thermal lensing is an interesting subject. No problem. Glad you got to the bottom of it.

[@fluiditynz]

I'm wondering if there's a catalyst in the acrylic that's not as transparent to the fibre laser light. My resin printer uses a UV curable catalyst, my polyester resins use an MEKP catalyst. Here's an old video showing marking extremely similar to yours,, done deliberately and discussing acrylic plastic manufacture: kzbin.info/www/bejne/g5LLc6CQa5t4pNE 2-part silicons use a zinc? or a platinum catalyst and likely there's one in epoxy and in polyurethane resins too.

[@SarbarMultimedia]

Hi Graham Subsequent research and knowledge gained elsewhere about materials and the way that they react to different light wavelenghts, revealed that at 1064nm acrylic is about 90% transparent. Thus, most of the light photons are passing through without colliding with anything solid.. Put it another way, just 10% are likely to hit a molecule where there will be an energy transfer. As I have seen with my many tests with CO2 and acrylic, hit the molecules with enough energy and they evaporate rather than experience a chemical change. However reheat the vapourised acrylic and it does chemically breakdown to flammable products. Microscopic inspection of the "bubbles" shows they are not bubbles but minute fracture planes with a distinct spot that indicated a mini internal explosion where expanding gas has internally fractured a little circular plane that looks very much like our galaxy..The fracture planes are totally random in size, disrtibution and orientation but all within a narrow zone that can be raised or lowered by moving the laserhead. My experience with this machine, even though it has a more complex multi element F thete lens is that it still has some of the weird "intensity" focus issues I was observing with the single ZnSe CO2 lens. Thus when the beam is focused (in the conventional way) onto the surface using a different material that absorbs the energy. Although many of those 10% collisions will be by insufficient photon energy. there are light rays close to the lens axis that are focusing at a different further point that are providing sufficient intensity to eveporate acrylic IF they collide with a molecule. So no complex physics after all, just building on the strange relationship that happens when you send a variable intensity laser beam through a lens. Whether there is aberration or not in the system, those rays right adjacent to the lens axis will never experience the same refraction s the general population and will always be forced to focus at a point beteween the nominal focus and infinity (at the lens axis) Best wishes Russ

[@williesims8655]

Hey Russ do you realize what your doing? you are colliding the beam this is how a 3d laser works, it puts two beams inside of the work at the same spot this creates a "dot" inside of the material a 3d printer uses two galvo heads that aims the beams in an x and y orientation to create the effect

[@SarbarMultimedia]

Hi Willy I am aware of the intersecting beam principle but it also requires a special type of glass (or plastic ) I believe to achieve the micro bubbles. As you will observe in my tests , there is no real controllability of pattern to my internal vaporisation, it happened at random depths for each pulse. Concentrated light energy at a specific point seems to be the cause of this effect but this indicates a varying focus of energy (from a single beam) for each pulse rather than a controlled intersection of two distinct beams. My original first thought was the sort of idea you propose. I thought it was a reflected beam intersecting with the original incoming beam. . However, removing any chance of reflection soon killed this idea. Hence my one beam variable focus point per pulse seems to be the only theory that fits the observations. Best wishes Russ

[@TMS5100]

glass is normally used for this type of engraving. plastic is far too inconsistent for clean engraves. maker's muse on subsurface engraving: kzbin.info/www/bejne/qYDVk6xsbpeIl8k here is a good video of one in action. the optics are really quite different from normal fiber engraving machines and they have a Z axis platform. kzbin.info/www/bejne/gnupYoaQndN9p80

[@gzhighpoint]

Acrylic burs are annoying. My company has a good way to deal with it conveniently to keep it clean and translucent.

[@gavins7542]

cool. but looking at it it looks nasty af