RDWorks Learning Lab 202 More Laser Cutting Investigations

Despite trawling through many research papers. I have found no explanation as to why and how a laser beam cuts materials. We all know it does so because of the FOCUSSING power of a lens. We have all used a magnifying glass to focus sunlight onto a piece of paper and found that it burns a hole (or fries ants!!!!) BUT it ONLY works at one FOCAL POINT. Drop the paper away by a few mm and the effect is zero. This in itself poses a logical question. When we focus a laser beam onto the SURFACE of the material we get what we expect , a burnt dot, but below that focal point according to all lens theory ( and the magnifying glass proof) the beam is losing its burning power .......how therefore can it cut a parallel kerf many millimeters deep????? The problem has been around for ever and, despite my failure to find research on the subject, I feel sure that I am trying to reinvent the wheel....or am I?
In this session I push through methods of trying to "see" the beam in an effort to find an objective way to asses beam/lens performance in less crude manner than just cutting material..By the end of this session, I honestly believe I have opened a new exciting door to the future.