RDWorks Learning Lab 231 Search for a Beam Conditioner part 4

[@arminth]

I'd suggest a cold beer to cool down the two grey cells! 😁 I was thinking about if it would be possible to calculate the diameter of the'deadzone' of the lens by dividing the intensity of the beam by the first derivative of the function of the lens curve for a defined interval (not at 0 for sure but around 0). This will get a very big number which is getting smaller, the more off center you get. You get the point I am trying to aim at?

[@dannymiller2123]

Don't fret, Russ- you have yet to unlock the truly awesome power of the RF tube! It's not in spot size, which the diffraction rules and the Airy disk show you can't improve on once you have a good M2 factor. The true power is right in front of you, you just have to think about a completely different property and task!

[@SarbarMultimedia]

Hi Danny Your encouragement is more than helpful because it makes me research the subjects you speak of, I do not have the awesome knowledge of optics that allows you to visualize the effects I see in formulaic terms. From your previous guidance I have done much research into diffraction, airy discs, apertures, focus and spot size I cannot logically associate the subject with the effects I observe and demonstrate.. My simple two grey cells are however able to make sense of refraction laws. and how a spherical geometry lens surface can bend light into a theoretical point of singularity (almost). . However , at its limit that law will produce zero refraction if the beam is perpendicular to the surface ie a parallel sheet of any light transmitting medium will not cause a focus effect from a beam that is normal to its surface. Thus it follows that the axis of any lens, regardless of it defined focal point, cannot focus a beam that is coincident with its axis because there is no angular surface to refract the beam. This logical non-focusing property will gradually decrease and a focus will begin to form (rapidly decreasing from infinity) as the angle of incidence of the spherical surface increases with distance from the axis. I have no idea what the optical term for this lens blind spot is and in reality I imagine it to be unimportant when you are trying to focus an image. However I am not trying to focus an image. In simple mechanical terms I wish to use a lens as an intensity amplifier. BUT what I want to amplify is a pinprick of incredibly intense light that happens to coincide with the axis of the lens where little or no amplification is available. Hmmm that tells me I should give up!!! THAT is the real reason why I can demonstrate a parallel beam of light passing through the lenses, The longer the focal point, the flatter the spherical geometry at the axis and the bigger will be the non-focusing "blind spot" There is no hint of focus in any these beams , regardless of the focal distance. They are not performing in accordance with IMAGE driven concepts of lens theory. We are using lenses to amplify light INTENSITY because it is light intensity that causes material damage. The greater the intensity the faster you can do damage. I have already created a super intense beam band now I want to use a lens to amplify it even more ......but it wont. . Going to this small intense beam extreme is in itself educational because it clearly explains why you have to expand the beam. It is a mechanism for reducing the central intensity and negating the effect of the lens bind spot and using that part of the lens surface that DOES act as an intensity amplifier. However, what is being amplified is a castrated intensity profile that is much closer to the uniform light required by l lens imaging theory. I have already unlocked one awesome power aspect of this extreme intensity and that is by using a triple compound lens to do engraving way beyond the previous capabilities machine with its 30 watts and X2 beam expander. When I have finished exploring, I will go back and thoroughly experiment with the new engraving potential of this machine.. Thanks again for your contribution. I will continue hunting for ways to make 30 watts into a cutting monster. Best wishes Russ

[@dannymiller2123]

@@SarbarMultimedia The thing is, when lens aren''t in these novel configurations (backwards, etc) they are already in the best possible case, the "diffraction limited system", easily achievable with the off-the-shelf optics and an RF tube. The quality of the lens and the spherical aberration error are insignificant when you are a DLS thus nothing to improve upon. When you are a DLS of a particular wavelength, there is a fundamental tradeoff after the final lens- you can have a long, narrow cone with a high Depth of Focus (DoF), or a small minimum focal spot size. When you change from a 2" Focal Length lens to a longer 4" FL lens, you double the DoF which reduces the loss of energy intensity as you go +/- the focal point. But also fundamentally double the focal spot size, and thus reduce the best energy intensity there by a factor of 4. Conversely, for engraving we often want a tiny focal spot size to represent detail, and/or because we need the highest possible intensity to burn anodization off aluminum. Thus the 1.5" FL or 1" FL, which you have already experienced- along with the inherently short DoF, making it very sensitive any deviation from the focal point. Thus, while a good choice for fine engraving, it is rubbish for general cutting as its DoF is short. The thing is, the *exact same effect* occurs when you halve the beam size coming into the lens. This is counterintuitive, and where physics may appear to have gone mad- but this is due to the fundamental wave properties of light. Not the lens design nor quality of the lens as long as you are a DLS. Bottom line, the DLS rules mean that for a given wavelength there is a inherent best case of ratio of DoF to minimum focal spot size, and it is not possible to make it better. This is always true regardless of whether you vary the focal length of the lens, or beam diameter. They create the same effect and end up with the same limit. A 5mm 1/e^2 dia beam going into a 2" FL ZnSe meniscus lens will produce a 0.198mm dia focal spot. If you change to a 2.5mm beam diameter, the intuitive expectation would be a 0.1mm spot size- but that is not the nature of a DLS. Instead you get a 0.4mm dia focal spot! That is the best possible result. All cases where you deviate from a DLS mean a larger focal spot size for a given DoF, or a shorter DoF for the same focal spot size. Next up- not only are photons both a particle and a WAVE, they are inherently *quantum* objects. And under certain circumstances can do impossible, unthinkable things that, in rare cases, are empirically observable and you can never see the world the same way again once you understand what you are seeing.

[@jackflash6377]

Brilliant! I hear ya on the "two grey cells". I'm down to one grey cell some days. Very interesting observations and It feels like you're on to something. Definitely has my one brain cell active.

[@elsindo]

Great concept, Sir. I look forward to your success on it. I want to try it by my self but I kinda short of parts for the test. I have been studying about the correlation between air pressure and laser cutting profile regardless the type of the lens being used. Well, it cost so much time. But I think it's worth to dive deeper into it.

[@SarbarMultimedia]

Hi Ahmad, please note that this is not the normal glass tube laser machine. It uses an RF signal to drive the laser process. The performance characteristics of this RF technology cannot be immediately transferred to glass tube technology. So please be careful what you try to copy. Best wishes Russ

[@elsindo]

@@SarbarMultimedia I noticed that from your explanation through your video, Sir. And that's why I said "kinda short of parts". I use regular CO2 glass tubes and fiber laser for my daily activity. Not having any RF yet. One of the reason for not having any RF ones is I haven't complete my research on my existing machines. One at a time works better for me. One question, does air assist system or method or usage in RF laser has any differences with those in normal tube laser machine? I've been following your huge collection of videos and have been trying to catch up what you have researched. Cool channel you have, Sir. Oh.. Greeting from Indonesia and pardon my English. Not very fluent in it.

[@SarbarMultimedia]

@@elsindo Hi Ahmad The difference between RF and constant current glass tubes lasers is all to do with the science of creating a laser beam and not the beam . They both generate 10.6 micron wavelength electromagnetic waves and damage material with exactly the same energy transfer mechanism.. I created my budget RF machine by using a very basic low cost Chinese glass tube Ebay machine. For years I had been bombarded by marketing hype and fantastic performance promises from the likes of Trotec, Epilog and Universal .This low cost creation was my way of trying to discover the "magic" that these guys were selling. I spent several months testing and exploring this different laser technology only to discover a very expensive and complex technology that was inferior to glass tube science in just about every way possible. The massive disappointment is the reason why this machine sat unused in my workshop for 10 months, However, During those 10, months I have come to understand so much more about lenses and laser beams and discovered many ways they interact that are not accounted for by conventional lens theory. The very small and VERY intense beam created by an RF laser source is ALWAYS diluted by this beam expanding technology WHY? I saw tremendous potential in this high INTENSITY;laser source and thus I have tried to exploit the beam in its natural form. Experts predicted I was wasting my time because such an unconditioned beam was unusable. It,'s been an amazing experience to be able to prove something I predicted two years ago but never had the means of verifying that there is a non-focusing (a "hole") at the center of all lenses. I am trying to find new ways to turbo boost this RF technology to a point where I will enjoy using this technology. There may still be some REAL "magic to be discovered. Unless you have too much money, I would not rush out to buy into RF technology. Yes, the marketing hype is very persuasive but smoke and mirrors best describes it Best wishes Russ

[@elsindo]

@@SarbarMultimedia Hi again, Sir. Thank you for the reply. It is well explained and I think I will just continue my research in regular laser tube regarding the tremendous price of the RFs. Again... Thank you.

[@FranciKapel]

Great session. Do you think that middle flat part of lens is influenced by lens width or only by focal length - curvature? And I believe you mentioned in the past that lens made of different material can have the same focal length but different curvature... So lens with the same focal length can produce different cutting width? Interesting stuff :)

[@tabasdezh]

Great video... thanks for sharing.

[@gunterpietzsch3995]

I'm pretty sure there is an additional third grey cell somewhere hidden in the background.

[@TEACypher]

Evening Russ just found your channel, usful info, watched your buying video, and was wondering if you had though on the red dragon 50w machine, uk based company so maybe avoids some of the risk.

[@SarbarMultimedia]

Sadly , buying a machine in your own country does not mean anything. The Red Dragon machines are Chinese made imports from the E bay factories. Such companies may or may not do setting and test work and QA with the machine before shipping to you. Thinklaser do a real test and QA job and provide a an expert service engineers and spares backup service. These are made n China but to a completely different specification . Somebody has to pay for that service so a £1500 ebay machine that you buy as a "project" will now become a £5000 plug and play trouble-free machine.. For something that is genuinely built and designed in the UK you must look at Lotus Laser. They may look Chinese but that's because the case is imported from China. But now you are into £7000 bracket.. You should not fear buying a cheap Chinese machine if you realize it will require a new tube and power supply immediately so add £400 to the price you pay.. It will still require your TLC, time and perseverance. The essence of a good reliable machine is there if you have the skill to make it happen. It also means you become your own 24/7 service tech and do not have to buy services. i thinks that there is little comfort in buying an Ebay type machine via a company like Red Dragon.. If you are trying to start a small business then its a no brainier, you need to speak to Thinklaser or Lotus laser so that you hit the ground running and will do so with confidence about the future. Best wishes Russ

[@sz72909]

Isn't it true, though, that the central area of a lens that you are calling a "dead" zone will pass the central rays of the beam through WITHOUT much focusing, but nonetheless pass them through until at some point the outer rays are focused and combined with those straight bunch of rays? We are not losing those rays' intensity, we are just not refracting (bending) them. Also, the conical burns you are getting into the acrylic cubes are shaped that way by the fact that the narrow point at the end is burning (or melting) the acrylic for a shorter time interval than the parts on the top of the block (where the beam enters). The reason the latter is a wider circle, also depends on time. It is the part that is exposed to the beam the longest, thus the weaker rays are getting a longer time to burn a bigger circle. I hope I have expressed myself well enough to be clear.

[@SarbarMultimedia]

Hi Please excuse my non-scientific description of what I observe but this very small high intensity beam is creating some weird and unexpected effects as it passes through various lenses.If you have seen any of my previous sessions and know what a raw beam mode burn is ( without a lens) . When passing that beam through a lens, it does indeed do as you say, it refracts the outer rays more than the central rays to achieve a compression of the beam whereby its total energy density is amplified to a maximum at some sort if "fuzzy" focal point. However, try to imagine what is happening at that plane of focus. The outer rays have very little intensity but are being refracted into this focal spot at a more acute angle than those much higher intensity rays at the beam axis. The important concept here is that a lens does not change the intensity properties of a single ray (if you can imagine such a thing) it only changes its direction. If you take that concept to the very central and most intense ray at the axis of the beam , it logically must pass through the lens with zero direction change and zero intensity change. Light travels in straight lines so it is only at this focal plane that the corralling of RAYS reaches maximum density. Lets now attach different intensity values to each ray and step back to the raw beam. It had a Gaussian intensity distribution. If I pass it through a lens with infinite focal length ( a sheet of glass) It will still emerge as a Gaussian distribution., Now start decreasing the focal length little by little and imagine what you are doing to that INTENSITY distribution.. The outer intensities are being aggregated whilst those closer to the beam axis are little affected. So what do you imagine the intensity profile looks like at the focal point? As I have mentioned often, I am not an optical engineer, my analysis of how lenses work is a very elemental mechanical engineering dissection. If you can accept the visualization I describe above you will understand the logic of that central RAY being totally unaffected by a lens. Many thanks for the comment because in dragging up an answer, it often helps clarify or reinforce my own thinking. I am equally open to change by logical arguments. I find it fascinating that lenses and laser beams have such an unusual relationship and all because of variable intensity. Best wishes Russ

[@joefleming8568]

Excellent Work !!

[@craterinahole]

I don't know what I'm talking about, but wouldn't you expect a smaller diameter lens at the same supposed focal length to have more curvature? Could you pass your new intense beam through a smaller diameter lens and expect less of a dead zone in the center of the lens, assuming it's the same focal length?

[@SarbarMultimedia]

Hi The geometry of a lens is based on spherical radius.. The bigger the sphere the longer the focal length. If you cut a slice off the sphere then that will be a lens. I hope you can now see that the thicker the slice the bigger the diameter will be. So diameter has nothing to do with focal length . It's just the spherical curvature of the surface that determines the focla length. Best wishes Russ

[@ForgeKnife]

First comment, intensity is a photometric term describing how bright a light source appears to your eye. Since you are measuring laser energy in Watts and you are interested in the amount hitting a surface the proper term is irradiance. The CO2 laser emission is 10.6 um and is invisible so technically it is not light. Light is defined as the wavelength between 0.3 and 0.7 um but everyone uses slang so we know what you mean. Second comment, when you stop down a lens you get a greater depth of focus, I think this agrees with what you are seeing. When you use more of the lens you should get a finer spot size and less depth of focus assuming that you are below the ablation threshold. Once above the ablation threshold you will not see the effect because the substrate is damaged destroying any fine detail. Of course the laser is multi mode so you don’t have a single well defined gaussian beam but multiple spots that are not stable. Of course it looks gaussian over long exposure time with high energy that ablates the acrylic and you are dealing with huge spot size and are only interested in cutting so none of that matters anyway.

[@SarbarMultimedia]

Hi Ernie Thanks for your comment because I enjoy great technical feed back. It makes me stop and think. I very purposely use the term INTENSITY to describe the part of the laser beam that interests me because it is more visually descriptive than energy density, flux density or irradiance . So please forgive my liberty taking..... after all this is shed science and as you see I have no respect for theory and rules. I know that high intensity light can damage material faster than low intensity light. Thus the amazingly small and ultra intense beam direct from this 30 watt tube has more cutting potential than my 70 watt glass tube with its 8 or 10mm beam. I see a lens as nothing more than an intensity amplifier so if I put an already intense small beam into a lens, I expected to get a significant intensity amplification. With all my lens testing, I have used a conventional CO2 glass tube beam with a much "softer" intensity profile. This RF tube has allowed me to investigate the effect of different beam expanders. I already established that a X2 beam expander cuts better than a X3 beam expander purely because as you increase the beam size you decrease the maximum intensity. Less intensity= less efficient cutting. My search for the impossible (so I have been told), a x1 expander that retains the diameter and intensity of the beam over the work area , was not quite achieved, but nearly. This ultra small high intesity beam has allowed me to prove a lens property that I started discussing 2 or 3 years ago as I searched for the mechanism by which lenses to cut deep and straight. This ineffective focus zone adjacent to the lens axis is proved beyond doubt in my final demonstrations. That 190mm focal length lens produces a line thickness of about 0.3 when used on my glass tube machine. Pass a 5mm intense beam through it and it now burns a 4mm wide line.. . As with all theories, there are limiting conditions ans I think what I am seeing is unexpected and outsde the scope of lens theory. Lens theory has remained unaltered for several thousand years and lasers were not around for Kepler and Galileo to include in their experiments. I see no stopping down in what i am doing to explain the huge depth of field I am achieving. this light is not passing through an aperture , all I am doing is effectively zooming with different focal length lenses This clearly demonstrates why everyone uses a beam expander to control their RF machines. A larger beam reduces the central intensity to a point where any "leakage" through the "hole" becomes insignificant however it dramatically reduces cutting potential . A well focused spot from a near uniform beam (as you say) is great for engraving. However as I have discovered. it is a weak well-focused spot. This 30 watts runs out of engraving capability at about 400mm/s This super intense beam even passing through a 3 stage compond lens, now has the ability to run at 600mm/s and I have yet to experiment as to just how fast I can really go. Although it looks like failure so far, the knowledge gained will allow me to revise my parameters and I still feel confident of improved cutting performance by manipulating the shape (intensity profile) of the beam Best wishes Russ

[@caraeriu]

I assume tipping the lens would do the same as offsetting the beam?

[@newmonengineering]

So on the answer to use a smaller diameter lens that just captures the intensity of the outer beam and therefore has a smaller radius which means the center portion of the beam has a smaller dead zone to pass through?

[@SarbarMultimedia]

We must be very clear here to understand the limitations of my test I absolutely know that high intensity= fast cutting. With a glass tube the shape of the beam starts off large between 6 and 10mm diameter typically. At full power the beam is pretty pointed because there is a certain max intensity that the tube can create. With a glass tube when you reduce the power the beam diameter does not change but the shape of the intensity profile does. It gets "blunter"intensity

[@SteveN-bh3wv]

It's not a diffraction effect. When you are focused on the surface, you get waveguiding and end up with a straighter edge.

[@DesignCutters]

What if the light is thought of as a liquid and the lens is a hose nozzle. Forcing the liquid through a smaller nozzle results in greater damage, as in pressure washing. Could there be such a thing as forcing the light through a quartz crystal or similar crystal shape rather than commonly shaped laser lenses? Just mentally rambling here on too much coffee.

[@SarbarMultimedia]

Several small problems with your suggestion. First there are very few materials that transmit 10.6 micron light and I am using two of the most common (ZnSe and GaAs) . Try firing your beam at a tray of sand (quarts crystals) and see what happens. Secondly , liquid is not even a close analog for light but if you need some sort of imaginary liquid model then it is the laser beam itself which is the high pressure water coming out of the hose nozzle. Now point that high pressure jet at a small hole in a flat surface. If the hole is smaller than the jet then any water that cannot get through the hole will just splash back. That hole will do nothing to further increase the pressure. Sounds as though that coffee may be tainted with something "interesting" Best wishes Russ

[@customsolutionsinc]

sounds like we almost need a hybrid lense that is more conical, with slight curves on the slopes. Next question is where to have them made....lol

[@SarbarMultimedia]

Conical lenses are called axicons and there are lenses with compound geometry (and supposedly zero aberration) called aspheric lenses. Available at a cost that is outside the price range of a typical hobbyist. Just Google these descriptions and there are lots of manufacturers. With sophisticated CNC equipment almost ant shape is possible. Best wishes Russ.

[@elsindo]

That's a great idea..... With a great great price as well..

[@francoad]

Is there a way to order your papers on how to print a photo using the laser?

[@SarbarMultimedia]

Hi Franco If you add another comment that contains your disguised email address then I will send you a data pack. Disguising your address used to be fairly simple but recently KZbin has implemented algorithms that detect bits of email addresses and prevents publication. We now have to be smarter than the algorithm. You have to describe your email as part of one or two sentences, so here is an example. Start with john and then after a dot add smith. Use the normal at symbol followed by this backwards liamg plus a dot and a com. I will delete you comment as I reply Best wishes Russ

[@francoad]

@@SarbarMultimedia hi yes it is "franco" then "ad" the at symbol and I really like yahoo

[@francoad]

Thank you!

[@polakis1975]

Windy outside 😁

[@aaronanthonymoat]

Do you have a Patreon channel? The reason I ask is it could help you fund your designs. I think your onto something big. Thanks

[@SarbarMultimedia]

H Aaron I do what I do for very selfish reasons. Self-education, engineering pleasure and as a means of creating video material for editing (my other hobby). This laser technology was never intended for any business purpose, just an escape from the "project engineer" in my life. Every knowledgeable optical engineer tells me I'm wasting my time. However there are many observations that I make in my weird experiments that do not seem to accord with conventional wisdom Those are the sort of problems I really enjoy. Whether I succeed or fail is of no consequence because even failure is a learning experience. So no, I do not try to monetize what I do. However I greatly appreciate the thought. Best wishes Russ