Laser Beams and Lenses Two Unruly Teenagers Pt2
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- čas přidán 30. 07. 2023
- 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 componets that seem to work sufficiently well and require no close scutiny.
As user of laser technology I have noticed many detailed inconsistencies , particularly with lenses and ther performance with a laser beams. I have known for a long time that lens design is based on transmitting normal light images. Passing a laser beam through a lens is a completely different application and superficially seems to sort of work. However, closer 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 examined in detail what the laser tube manufactuer is selling us and the problems that we all ignore. In this 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. - Věda a technologie
Great work! Real life expirience and hard work...
Thanks
This class blew my mind. Thanks.
You, Sir, are an absolute TREASURE! Thank you!
Immense amount of work! The conclusion is very surprising and extremely interesting. Also, I now understand why you wouldn't recommend a Reci tube. Thank you!
I love listening to all the great advice and explanation you're sharing with us! Thanks!!!
I appreciate your concern, Many thanks. However the guy running the site is a longtime laser indusrty friend and he has my full premissions. He attempts to be a cenralised source for all things laser, including all the official Lightburn Tuotorials and another series about the lightblade machine where he works. (Thinklaser)
Hmmm..... So where does that leave us? I guess I'll just have to wait for part 3.
I thought you did this test years ago. You did cutting tests, then changed tubes and it cut better with the high quality tube.
Your memeory is pretty good but I didn't change it for cutting issues. I pointed out that it was cutting fine but that I could not get the precision dots I wanted for my photo engraving. I have yet to test the contrast between these beams with the compound lens I use for engraving. This was a straight comparison between simple plano convex lenses that most people use to show that lenses are not the perfect devices that we all believe in and that when you pass a laser beam through them there are conflicting properties of each that cause all sorts of detail issues. Many thnks for the reminder
Great video Russ! Question: My lens holder/3rd mirror is not perpendicular to the cut surface. There aren't any adjustment screws to change the angle, and I can't seem to find a new adjustable mount for the lens holder/3rd mirror. Any ideas?
Can you help me fine a way to test the tubes and powers supply's. I got a Golden Laser and was told it worked. Yes the x and y move but didn't notes there was no burn marks on the grid.
Very interesting how does this change if you use 2 lens? Do we lose power as it passes through or do we get a better force?
Hi Joseph.
As you work through my videos you wll seet that at one stage I tried to amplify the inensity effect of a beam by using various pairs of different focal length lenses. In the case of creating a super small clean dot, I succeded but when I tried to use two lenses for increasing cutting speed/depth I came across a brickwall. Lenses are designed with a focal distance based on the assmption that the rays entering the lens will e parallel. If you use one lens to focus the beam down to a smaller size then two issues ensue. First the rays are now converging at the second lens so this automatically reduces the focal length of the second lens. The smaller beam hitting the second lens is now not a Gaussian distribution (because of spherical aberration) and is being poorly focused by the less refractive geometry at the centre of the second lens. If the lenses are touching (as with the short focussing compond lens system I designed for photo engraving) this effect is not important, however putting distance between the lenses does not have the expected intensity amplification effect you would imagine..
Ok I have a question: What type of lens ie. ZnSe,GaAs,Ge,CVD-ll-vl Znse for photo engraving is ideal.? I believe 1.5 is a good length but don't understand the types. Do you have a video on this subject. Thanks Joseph
@@josephlovell6951 Hi Joseph
Yes there are several videos on lense but it is all summed up in these two videos.
Forget germanium as a lens because after about 12 watts the power changes the crystal stucture of the lens and it becomes opaque for CO2 light.
The lenses we can buy for our machnes regardless of price or material, ALL possess an unbeatable physics property called spherical aberration. In normal lens use for telecopes . projectors, camaeras etc the light is always uniform intensity as it hits the lens.with parallel rays. Under these circumstances the standard laws of lens theory apply. However.we are not sending a uniform intensirty beaminto the lens and we are not trying to project/capture an IMAGE. Instead we are tring to intensify the intensity of the bean to damage material. An the golden rule for damaging material is " the greater the INTENSITY the FASTER you can do damage".
There are two lens forms we can buy. One is plano convex which has significant spherical aberration properties and is designed to be used flat side towards the work. The second type is a meniscus form where the lower face of the lens is concave,. This reduces the spherical aberrationeffect by about 90% and produces a pretty small concntrated spot size. This form of lens is ideal for engraving whereas the plano convex form, with its HORRIBLE optical properties. is actually more efficient at cutting.
There are basically only two types of lens material we can use .
1) Zinc Selenide
All ZnSe material is poor at transmittong CO2 light (about 70% efficient) and is toxic to handle. However, in the same way that you see a blue/mauve hue to camara and binocular lenses which is there to improve light transmission, so it is with ZnSe lenses. They are coated with several layers of exotic materials to provide an anti reflective coating to improve light transmission to 98% or better.. Althnough ZnSe can occur naturally it is always grown in a laboratoty (jusyt like silicon chips) The Chinese use a manufacturing technique called Physical Vapour Deposition (PVD) whereas the USA uses a process called Chemical Vapour Deposition (CVD). The PVD materal is limied to about 80 watts whereas the CVD material can handle up to about 200 watts . The ll-lV material is always CVD material and has a slightly more efficient anti refection coating. ..... but you pay a lot more for that 1 or 2% transmission improvement. Remember that ALL these lens types are designed and made according to factors defined by conventional lens theory so there is no significan difference in the GEOMETRY between any of these ZnSe lenses, they all perform the light intensification function in exactly the same way regardless of manufacturing process or price. By the way, the AR coating on the ZnSe makes it safe to handle but be careful if you break a lens.
2) Gallium Arsednide
This is a weird material because it is black and you cannot see through it. So you wonder how can it work as a lens? Light is equally unfathomable because at 12.640 nm wavelength this black material is transparent and allows the light through. This materail is even less efficient at transmitting light (about 60% efficient) but by adding exotic materials to produce an anti reflective coating, the transmission efficiency is again about 98% However there are two properties that sets this materiial apart fro any of the ZnSe products. First. it is mechanically stronger and will easily handle powers in excess of 500 watts . Second, it has a different refractive index that means that for a given focal distance the shape of the lens geometry is "flatter".
As I show in these two videos. the focussing effiiency of a lens is not constant, it depends on the INTENSITY distribution in your beam. For your RF machine the situation is very complex because your beam is being modified by a beam expander as soon as it exits the tube. This basically destroys the nice Gaussian intensity distribution and what is sent aroind your machine is an unpredictable intensity mess, The RF machine is pretty efficient at engraving (if you find out how to control your dot size) but it is very inefficient at cutting (yes I know it cuts) but the spherial aberration property of the lens can only be exploited by a decent Gaussial intensity distibution.
Finally if you are looking to produce the smalles dot you need a special compound lens with a very sort focal length (about 20mm) that I develoed and is on sale at C;loudray
see this www.cloudraylaser.com/collections/nozzles-lens-tube/products/cloudray-n04-universal-compond-engraving-nozzles and scroll down to see lots of detail. Sadly , Trotec have locked you into a rather expensive and inflexible lens mounting design and a high definition lens arrangement was never on their design radar. This means doing the best you can withthe shortest focal length lens available and see if it can be of meniscus form.
@@SarbarMultimedia thanks that is helpful