RDWorks Learning Lab 215. AT LAST!!! I understand how lenses cut. @SarbarMultimedia

Uploaded July 2021 | Updated September 2026, 1 week ago

I have struggled for 2 years to understand why conventional lens theory does not match the observable experimental laser cutting data. This session uses my new set of gallium arsenide lenses to create data sets from a mix of new and old experiments. Reverse engineering the ray paths and integrating my knowledge of how and why mode burns produce their erosion shapes, has allowed me to create scale CAD drawings for each of my 4 lens focal lengths. The end result is that my theory about projecting focal points below the normal focal point proved to be correct ......BUT is only a contributing and limiting factor for the cutting action that we observe. Damage to materials with light energy is totally dependent upon light INTENSITY ( some call it energy density) which my new model includes. However, the conventional lens theory models that you will encounter make no mention of this fact as you will see in the links that follow.

Here are links to credible sources that try explain how and why to use different focal length lenses but all are basing their messaging on standard white light visible optics lens theory (ray tracing).
American Photonics
youtube.com/watch?v=ykZScC5cuHA&t=26s
Trotec
youtube.com/watch?v=K_dKUsY05jY
Universal
youtube.com/watch?v=ykZScC5cuHA&t=26s
Epilog
support.epiloglaser.com/article/8205/42831/focus-lens-101

RDWorks Learning Lab 215. AT LAST!!! I understand how lenses cut.

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$RDWorks Learning Lab 245 Lenses and Laser Beams A Marriage Made in Hell Lenses have worked perfectly for thousands of years BUT laser beams have only been around for about 60 years Yes, its still light waves/rays and will be refracted by lenses in exactly the same manner as always. Normal light is more or less uniform intensity across the surface of a lens whereas the Gaussian profile of a laser beam means it has most of its light INTENSITY at and around the centre of the beam. Light refracts (bends) as it passes through a lens which is designed to direct all light energy to a common point (the focal point). This means the outer edge of a lens must refract the rays more than those at the centre. Our laser machine lenses are manufactured with the age old (and simplest to manufacture) form of lens geometry.....spherical. This shape has imperfect focusing properties called aberration. Thus, light from the outer edge of a lens focuses at different points to that through the center. For uniform light this weakness is hardly noticable, perhaps a bit of blur if you look carefully. However, for a laser beam with its maximum intensity (its max ability to damager material) at the beam axis, this becomes a problem. A lens may have a nominal focal point that would apply to normal light, but pass laser light through it and the maximum intensity at the axis of the beam meets the least refractive axis of the lens. Bad news. Hence the title of this video.......they stay married (with all the imperfections) for the sake of the children and to the outside world all seems well. This video is some background about several months of test work I have conducted using various beam sizes and many lens types to examine the inner workings of this imperfect marriage. Most will not be interested in the large report of my tests and findings because on the surface, laser machines do aproximately what is expected of them without ever needing to lift the hood. If you have an interest in the report I produced then please contact me via this private contact form. https://forms.zohopublic.eu/ndeavorlimited/form/K40XtreeemLaserCutterContactRussSadler/formperma/k2Cn0QN5ChpazfTMAUw25lZ-FKpjZa96TQWHjv3ntOg$

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