Laser Beams and lenses Two Unruly Teenagers Pt1
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- Опубликовано: 30 июн 2024
- We use laser beams and lenses on all our laser machines and we take them at face value, trusting reputable manufacturers' specification sheets. The problem is that laser machine builders are not cash gobbling research institutes. they need to be efficient profit making organizations. Hence they put their trust in top quality components that seem to work sufficiently well and require no close scutiny.
As a user of laser technology, I have noticed many detailed inconsistencies with these key elements of our machines that DO require much closer scutiny. I have known for a long time that lens design is based on transmitting normal light images and that passing a laser beam through a lens is a completely different application that exposes the inherent weakness of spherical lens geometry. Yes, superficially it seems to sort of work, however, forensic examination of that interaction has led me to gain a complete understanding of how the laser cutting mechanism works and In doing so it has raised serious questions about the laser beam itself .
In this 2 part series, I first examine what the laser tube manufactuers are selling us and the problems that we all ignore. In part 2, I look closely at how a lens works and what happens when it attempts to focus a laser beam. We all think we know the answer.... but even I was taken aback with the reality of that interaction. 
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I'm addicted to your videos, there's so much knowledge that leaves me excited. Thank you and greetings from Brazil.
Thanks for making these videos. Very helpful. I own a 60w co2 laser and these videos are really helpful to understand my machine in a deeper way.
Also, it looks like you too have fallen victim of one of those mugs with the ear attached upside down? I noticed it on a mug in my household as well. Someone was sleeping on their job.
Thanks again and keep up the good work with these videos!
Thank you for explaining all this!
A Photon decides to go on holiday, he turns up at his hotel and checks in... the concierge asks if he has any luggage, no says the photon, I'm travelling light.
EXCELLENT.? There is currently a debate about whether a photon is massless. It matters not to me.
Thank you very much for the great explanation.
Really great content, looking forward to more sessions
Part 2 is already edited and will be available tomorrow
Hey Russ, been watching your stuff on C)2 Chinese lasers since I got one in 2019. I pout a LOT of what you posted to work and have decent engravings and good cuts in various materials using Lightburn. I recently did some engravings for a plaque I made for our local AHL Hockey team and discovered I damaged the 2" (I think, need to verify), when I inadvertently forgot to turn the compressor on. The lens has a little spot on it so my power is reduced.
My question is, I eventually will need a new tube and plan to go up to a 100w from the 50/60 tube in there now that it came with, and I want to get as tight a kerf as I can going through 1/8 inch plywood for a project I am working on. I can't remember, do I go to a shorter length, like a 1" lens to tighten up the kerf? I think it originally came with a 1.5", but the lenses were crap, and based on your videos I went to 2" for better engravings without giving up on decent thickness cuts. What is the tightest kerf (dot) that these CO2 lasers can accomplish?
Hi
If your spot is just burnt on fumes then soak it for a few seconds with IPA and try to remove the spot with circular rubbing using a cotton bud. The antireflective coating is pretty duarable. Howver, if the debris has ben on there for a few minutes then the debris will absorb laser energy and heat the surface of the lens. That process could bake the fumes into the AR coating and the lens is likely to overheat with use and a cental star crack will happen. Lenses are the most vulnerable part of your machine, thus you should always have a spare lens.
The 50/60 watt tube supplied with your machine may not be what you think. . A typical 50 watt tube will be 1000mm long and 50mm diameter. It may claim to be 60 watts because that is waht it was test at innthe factory .... but that is not for you to use as it will shorten the tube life, 200mA is the max to run a 50 watt tube at. However, that 50 watt tube is almost certainly a B grade tube with a poor intensity profile. B grade does not mean crap but if you watch part 2 of this video you will see me running a B grade tube in one of my machines. Because I now understand how lenses and laser beams interact I have paired this 70 watt beam with a 2,5" GaAs lens and it cuts very well.
Your question about tube upgrade is an intersting one. AS the power of a tube increases so does the beam diameter. This could mean the the intesity gain is not proprtional to your expectations. I have found that the best "jack of all trades " tubes are in the 70 to 80wttt range. Steer clear of Reci (despite their good reputation). I have ssen far too many that are rubbish at low power Why pay twice the price for something that does not deliver across the range. Amongst the rest, Yongli, EFR and SPT, I would rate SPT as the best value for money. You can buy an A grade SPT rebadged (officially) as a CR70 or CR90 from Cloudray.. Fof a small kerf on thin material I would use a 1.5" (38.1mm) meniscis lens. There are all sorts of "opinions" about lenses and getting what you pay for, The facts are simple, The geometry of a lens logically has to be the same no matter who makes it and how much ir costs. Cost is generally related to the quality of the material and the materials manufacturing process, USA on a lens description means it is made with CVD ZnSe which is bright yellow and can withstand power in excess of 200 watts. The brown honey coloured material is Chines manufactured PVD ZnSe which ir rated at about 80 watts. That's another reason for staying below 80 watts with your tube, you can use cheap lenses. I have tested the power transmission and cutting performance of almost every lens available and higher cost does not get you better performsnce, One final point (myth) about lenses. A bright yellow CVD lens looks crystal clear to our eyes whereas the brown Chinese PVD lenses look rather dull and unexciting. OK. if that is your judgment of lens quality, how do you explain the BLACK galliun arsenide lens? We "see"in the 400 to 700nm wavelength range the light passing through these materials is at 10,640nm. So what you see is not what is actually happening. At that wavelength my black gallium arsenide lens is transparent Weird?
Best wishes
Russ
@@SarbarMultimedia Thanks Russ. I rarely hit 18 mA on mine and have the power turned down to 80% max at the controller, so 100% in lightburn is 80% at the machine. Tube still going strong 5 years now. Reason to step up to 100W is to cut thicker material in the 1/4 to 3/8" range for some projects. Also great info on Reci tubes, so I will look into the other tubes at Cloudray. I also replaced the Chaser lens soon after watching your earlier videos on lenses, and put a lot of what you taught to practice. Right now I just want to get a tighter cut for a couple projects, so will look into the 1.5" setup. Will also see if that is just a surface spot or actual damage. Going to tie the pressure switch into my relay setup that turns air on and off, so the tube wont fire if there is no air pressure, I missed that somehow.
I've also put your acrylic cutting and etching to good use, and yes, keep the machine clean, don't want a grid fire. I appreciate all the work you put into these videos.
Russ, I hope you're doing well. I has a project a few weeks ago where I needed a 5" lens. I bought one and tried to focus it but I could not get it to focus smaller than about 1.5mm or 2mm. Not sure why?? Is that normal??
Hi John
As I mention nin this video, lenses are not the simple bits of curved galss that most people think they are. Pass a laser beam through them and the outcome can be a lot different than what you expect.. The onl reason most peple would want to use a long focus lens like your 5" is because thay plan to cut thick material such as foam. (is that you?)
Whatbhappens at and beyond the focal point is very dependent on the material you are using the power and the speed. Although it will not be perfect , the best shot at setting the focal length is to set the optical focal point. ie 5" from the flat face of the lens Where the actual INTENSITY focal point is could be several mm awaymaybe 5.2 or mare inches, The longer the focal length the flatter the lenseand therefore a lot of very small refraction at and around the axis of the lens. This is the reason for poor focus. You may well find that turning the lens over produced a better smaller focal point.......but is does depend on speed power and material. Who said lenses were simple bits of glass? . You will also find that you gett a better focal point futhest away from the tube in one corner of your table. Have you done a couple of corner mode burns into acrylic as I do in this video to examine tou beam intensity profile at opposite corners of yoir machine. . Tell me what materialyou were trying to cu and what power is your laser. I may be able to be more specific with my answer and make an alternative suggestion.
Best wishes Russ
Can you refocus the beam with a magnetic field?
Nice idea but sadly light is not made up of charged particles The pink beam in the tube is ionized nitrogen and can be steered and focused by magnetism ....but not the laser beam itself.
But there are other types of lenses. The Axicon lens can help you with your problems with the focus dead range of the normal lenses.
Hi
Thanks for the thought. My aim is to investigate the commercially available lenses and laser tubes that everyone currnently uses. Although I have seen ZnSe axicon and aspheric lenses for specialist laser applications, the cost of obtaining the right size lenses (18 or 20mm diameter) to evaluate their cutting properties, is beyong my budget. The fact that cutting relies on the aberraion properties of a normal spherical geomety lens and the distribution of intensity within the laser beam. implies that a perfectly focusing lens will not be the panacea for efficient cutting. However, I will run with your suggestion and see if I can obtain any such special lenses from my contacts in China.
Thanks again.
@@russsadler3471 Yes, both types of lenses cost $600 and more, but I understand that absolute focus is not important for cutting. I own Trotec laser machines and am no longer willing to pay the cost for these machines. Therefore I rebuild China lasers myself and it has been shown that good optics and servo motors can compensate so much that apart from the software no brand machine is needed. The advantage of an Axicon lens in combination with a miniscus lens is that you can bypass the dead zone of the lens and thus have a very even focus over a longer focus range, which you want to have for cutting. Since I cut a lot of acrylic and value very high quality edges, I am now working with apertures to filter the beam.
@@shadowrob7709
Hi again. Thanks for your additional information that paints an interesting picture. As far as I am aware, Trotec always use an RF CO2 laser source which has significantly different beam mintensity properties to a glass tube constant current source. The huge divergence from an RF source (7 or 8 millirads) is usually corrected right out of the tube with a beam expander. This device uses two spherical geometry lenses, each with a degree of aberration. Thus when the beam appears in the real world its internsity distribution is already corrupted and reduced , no longer being the Gaussian distribution that entered the expander. You can easily verify this fact with a mode burn (without the lens) at the table closest to the beam source. and then repeating this test at the other diagonal extremity where the beam is at it's furthest from the source and an even lower intensity. I have a DIY copy of a Trotec RF machine because I wanted to discover the so calleds "magic" of RF technology. I was very disappointed and discovered why it was great at engraving but poor at cutting. Hence I would be interested to know if the beam you are working with is is an expanded RF beam. I note with intrest that Trotec are now selling a mixed technology machine with RF for engraving and constant current for "efficient" cutting.
Thanks again for your sharing and stimulating new areas for research
I presume you are using the Axicon lens flat side towards the source? and a meniscus lens with the convex side towards the source also?.. What sort of focal distance is the meniscus lensand what cone anglr is the Axicon? Is there a specific diatance you set between this compound arrangement? If I can get an axicon then I would like to understand how this can possibly enhance the central intensity that is so important for cutting . Thanks again for sharing such an intriguing topic,
@@russsadler3471 i use a 2.0° Axicon lens. the more acute the angle, the less dead zone you have. i'm still trying out the miniscus lise, i'm waiting for my tube with thread to arrive so i can set the distance precisely. But I assume that I need a larger focus lens because of the angle of incidence to get a greater focal depth. I tested with 2" but that was too short. Forgotten, yes the lenses are arranged exactly as you said. My first test was so that the focal length no longer had any influence on the laser slit directly.
Hi Russ, hope all is good, been watching the channel for a couple of years now. I'm trying to resolve a problem, I have a bad stepper motor & really struggling to find a UK supplier, hoping you can point me in the right direction... Model Red Blk laser - motor 57bhh51-280a-25c
Thanks Phil
Hi Phil
Tthis is just a standard NEMA 23 frame size stepper with 200 steps per rev. It is unlikeley your machine has a feed back system for the motor , I see no clue in the part number.
en.cwmotor.cn/product/36.html
Just measure the length of the motot (I guess it's 51mm long .... one of the cheapest and weakest) and you will be able to find this (4 wire?) motor at several UK stoockists. Just check the shaft diameter is 6.35mm . Check if has 4 or 6 wire out of the motor.
Try Ooznest. in Brentwood Essex 01277 523171
ooznest.co.uk/product/nema23-stepper-motors/
Speak to them and tell them what you have and they will sell you a close match. If it's a bit longer . no matter it will be a bit more powerful. Your driver will take it Just in case they ask. make a note of the black box driver model.
Here is an equivalent from Cloudray ( about 14 days from China) www.cloudraylaser.com/products/cloudray-55mm-0-9n-m-2-8a-2-phase-nema23-open-loop-stepper-motor?_pos=46&_sid=5e92cdfc8&_ss=r
Best wishes
Russ