Investigation of the transient coupling between the dynamic laser beam absorptance and the melt pool - vapor depression morphology in laser powder bed fusion process

•High-fidelity ray-tracing model to study multiple reflections induced beam trapping.•Investigation of coupling between optical and thermo-hydrodynamical phenomena.•Absorption dynamics in powder bed and vapor depression for different melting modes.•Results reveal highly non-linear fluctuating behavior of absorption for keyhole mode.•Validation with in-situ X-ray imaging and in-house performed single-track experiments.