Detailed knowledge about the laser-material interaction, especially the distribution of laser power absorption, is a prerequisite for the simulation and optimization of laser material processing. In this work, an algorithm based on ray tracing is presented to calculate the propagation and the absorption of a laser beam inside a complex 3D cutting kerf. To model the laser beam precisely, a ray source based on high-power intensity measurements of the laser beam emitted from a highly multimode step-index fiber is set up. For the 3D reconstruction of the cutting kerf geometry, a semicircle model derived from three characteristic lines of so-called "frozen cuts" is applied. The presented approach enables a direct simulation of the laser absorption inside the cutting kerf considering light propagation properties like beam degeneration, shadowing effects, and multiple reflections. As a benchmark, it is finally applied to analyze cutting experiments in stainless steel with an axicon telescope. [ABSTRACT FROM AUTHOR]